SHOTCRETE STRUCTURAL TESTING OF THIN LINERS -...

Report No. FRA-OR&D-75-91

SHOTCRETE

STRUCTURAL TESTING OF THIN LINERS

AUGUST,1975

FINAL REPORT

Prepared for

Department of Transportation FEDERAL RAILROAD ADMINISTRATION

Washington, D.C. 20590

NOTICE

This document is disseminated under the sponsorship of the Department of Transportation in the interest of in formation exchange. The United States Government assumes no liability for its contents or use thereof.

Technical ~eport Documentation Page

,--,,-1-. -:-R-ep-o-rt_N_o_----------,--72 .--:-Go-v-er-nm-e-nt-A,-c-ce-s-si-on- Nc:-o-.-- - - ----,-3,-.-R-e-ci-pi-en-t',-s-::C-at--,ol,-og-N,.,-a-.-------,

FRA OR&D 75-91 4 . Title and Subtitle 5 . Report Date

Shotcrete: Structural Testing of Thin Liners August 1975 6 . Performing Orgoni zation Code

,___ ____________ _,

1--------------------------~8. Performing Organization Report No. 7. Author 1 s )

G. Fernandez-Delgado, J. Mahar, E. Cording 9 . Performing Orgoni zotion Nome and Address

Department of Civil Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801

~-------------------------12. Sponsor ing Agency Nome and Address

Federal Railroad Administration Department of Transportation Washington, D. C. 20590

15 . Supplementary Notes

16. Abstract

UILU-ENG-75-2015 10 . Wark Unit No . (TRAIS)

11 . Contract or Grant No .

DOT FR 30022 13. Type of Report and Period Covered

August 1974 - August 1975 Final Report

14. Sponsoring Agency Code

This report presents the results of engineering studies related to the development of new and improved tunnel support systems. Thin shotcrete layers were studied to assess their capacity and behavior as temporary tunnel supports.

The design, construction, and operation of a large-scale test facility simulating a planar tunnel roof with a punching block 2 ft x 2 ft (60.8 cm x 60.8 cm) are described. Preliminary tests were conducted using thin mortar layers to assess the performance of the test device and the principal variables controlling the capacity of the thin liner. Results obtained from these tests were used in the planning and evaluating of the shotcrete test program.

This report describes the development of the test-device, the equipment, and its arrangement and the shotcrete used in the model. The capacity of shotcrete layers for different thickness and strength of shotcrete and shotcrete-rock bond was determined.

Two principal modes of failure, diagonal tension in the shotcrete and progressive separation of the layer from the wall (adhesion), were obtained. When progressive separation occurred and boundaries were present in the model, the layer retained a residual capacity and a bending failure developed for large displacements of the punching block. Steel fiber reinforced shotcrete showed greater ductility but had approximately the same load-carrying capacity as conventional shotcrete.

17. Key Words

Shotcrete; Tunnel Supports; Tunnel Liners; Thin Shotcrete Liners

18, Distribution Statement

Document is available to the public through the Nat ional Technical Information Service, Springfield, VA 22151

19. Security Clossif. (of this report) 20. Security Clossif. (of this page) 21. No . of Pages 22. Price

Unc lass ifi ed Unc lass ifi ed 219

Form DOT F 1700.7 (8-72) Reproduction of completed poge authorized

i.

01101

TF

PREFACE

This study was performed by the Department of Civil Engineering

of the University of Illinois at Urbana-Champaign, Urbana, Illinois from

August 1974 to August 1975. The pr~ject was sponsored by the Federal Rail

road Administration, Department of Transportation, through contract No.

DOT FR 30022, under the technical direction of Mr. William N. Lucke. Super

vision and coordination of the entire project was performed by Dr. Stanley

Paul. Dr. Paul also contributed many ideas and participated in the lively

discussions which stemmed from this work.

Mr. Harvey Parker contributed many original ideas and did much

to assist in the performance and analysis of these tests.

Construction of the test facility, shooting of the specimens and

experimental and field testing was assisted by R. Castelli, L. Lorig, and

W. Wue 11 ner.

Special assistance in organizing and developing the shotcrete

operation and providing good quality shotcrete was given by Mr. Warren

Alvarez and Mr. Jan Blanck.

Many valuable suggestions on the geotechnical significance of the

study and on the validity of the tests were provided by Dr. R. B. Peck and

Dr. 0. U. Deere who serve as consultants to the project.

The authors also wish to thank Mr. Paul Diemert and Mr. E. R.

Roger~ of Contractors Warehouse Inc. for providing us with a Reed Shotcrete

machine at a greatly reduced price.

iii

TABLE OF CONTENTS

Chapter Page

1 .

2.

. INTRODUCTION 1- l

3.

4.

5.

DESCRIPTION OF TEST DEVICE . . . . . 2-1

2 .1 2.2 2.3 2.4

REACTION ABUTMENT HYDRAULIC RAMS . . . . . . . FIXED WALL AND MOVABLE BLOCKS INSTRUMENTATION ..

PRELIMINARY TESTING PROGRAM .....

2-1 2-3 2-5 2-9

3-1

3.1 PREPARATION OF THE SPECIMENS . . . . . . 3-1 3.2 GEOMETRY AND BOUNDARY CONDITIONS OF TESTS ..... 3-2 3.3 MAIN VARIABLES AFFECTING THE STRUCTURAL BEHAVIOR OF

THE MORTAR LAYER. . . . . 3-4 3.4 LOADING PROCEDURE . . . . 3-14 3.5 TEST RESULTS . . . . . . . . 3-15 3.6 SIGNIFICANCE OF VARIABLES 3-71 3.7 CONCLUSIONS 3-83

SHOTCRETE TESTS ..... .

4 .1 4.2 4.3 4.4 4.5

INTRODUCTION .... SHOTCRETE OPERATION . SHOTCRETE TEST PROGRAM TEST RESULTS .................. . EVALUATION OF VARIABLES INFLUENCING THE STRUCTURAL BEHAVIOR OF THE LAYER

SUMMARY AND CONCLUSIONS ........ .

5. l 5.2 5.3

MAXIMUM RESISTANCE OF THE LAYER RESIDUAL RESISTANCE GENERAL CONCLUSIONS

4-1

4-1 4-2 4-19 4-26

4-59

5-1

5-1 5-3 5-4

REFERENCES

APPENDIX A

APPENDIX B

APPENDIX C

R-1

A-1

B4 l

C-1

V

LIST OF TABLES

Table Page

3. 1 MORTAR COMPONENTS IN 260 LB (118 kgm) BATCH 3-1

3.2 DIMENSIONS OF MORTAR LAYER . . . . . 3-6

3.3 MATERIAL PROPERTIES OF TEST SPECIMENS 3-12

3.4 MORTAR TEST RESULTS . ...... 3-27

3.5 VARIABLES COMPARED BETWEEN TESTS 3-72

4. 1 DRY MIX PROPORTIONS WITHOUT FIBER 4-5

4.2 DRY MIX PROPORTIONS WITH FIBER 4-6

4.3 MATERIAL PROPERTIES OF SHOTCRETE LAYERS . 4-20

4.4 SHOTCRETE LAYER TEST RESULTS ..... 4-28

4.5 VARIABLES COMPARED IN THE SHOTCRETE LAYER TESTS 4-61

C-1 SUMMARY OF ADHESION-TEST RESULTS TESTS S3 & S4 . C-5

C-2 SUMMARY OF ADHESION-TEST RESULTS TESTS S9 & SlO, C-6

C-3 SUMMARY OF ADHESION-TEST RESULTS TESTS S7 & S8. C-7

C-4 SUMMARY OF ADHESION-TEST RESULTS TESTS S11 & S12 C-8

vii

LIST OF FIGURES

Figure Page

l. l TYPICAL GEOMETRIC CONFIGURATIONS AND LOADING CONDITIONS IN TUNNELS INTERSECTED BY FLAT-LYING DISCONTINUITIES OR IN FLAT-ROOFED OPENINGS IN JOINTED ROCK . . . . . . . . . 1-3

l. 2 FIELD EXAMPLES OF TUNNELING IN 11 BLOCKY 11 ROCK MASS . . . 1-4

l. 3 PLANAR GEOMETRY OF TEST DEVICE FOR STRUCTURAL TESTS ON SHOTCRETE LAYERS . . . . . . . . . . . . . . . . . . . 1-5

1.4 FUTURE SHOTCRETE TESTS INVOLVING OTHER ROCK GEOMETRIES 1-7

2.1 OVERALL VIEW OF THE TESTING DEVICE 2-2

2.2 DETAIL OF RAMS-ABUTMENT CONNECTION 2-2

2.3 STEEL FRAME ASSURING VERTICAL AND HORIZONTAL ALIGMENT OF THE RAMS . . . . . . . . . . . . . . . . . 2-4

2.4 DETAIL VIEW OF RAM-MOVABLE BLOCK CONNECTION . . . . . . . 2-4

2.5 DIMENSIONS OF SURFACE SLAB AND HOLE PATTERNS FOR ATTACHING THEM . . . . . . . . . . . . 2-6

2.6 FRONT FACE OF THE FIXED WALL . . . . . . . . . . 2-7

2.7 FORMS AND REINFORCEMENT FOR THE FIXED SIDE BLOCKS 2-8

2.8 FORM AND REINFORCEMENT FOR THE MOVABLE BLOCKS . . 2-10

2.9 FORMS, MESH REINFORCEMENT AND THREADED INSERTS FOR SURFACE SLABS . . . . . . . . . . . . . . . . . . . . . . . . 2-10

2.10 FRONTAL DIAL GAGES AND STEEL FRAME SUPPORTING THEM 2-12

2.11 MORTAR SURFACE-DIAL GAGE BRACKET CONNECTION . 2-12

3. l PRE-TEST SURFACE CRACKS IN TEST NO. l . . . 3-3

3.2 APPEARANCE OF SPECIMEN NOS. 5 AND 6 IMMEDIATELY BEFORE TESTING . . . . . . . . . . . . . . . . . . . . . . . . 3-3

3.3 USE OF 6 X 18 IN. (152 X 457 MM) PLATES IN TEST NOS. 13 AND 14 TO SIMULATE ROCK BOLTING . . . . . . . . . . . . 3-5

ix

3.4 USE OF 16 X 24 IN. (406 X 609 MM) PLATES IN TEST NOS. 17 AND 18 TO SIMULATE ROC K BOLTING ........... , . , 3-5

3.5 SCHEMATIC DIAGRAM SHOWING TWO TYPES OF FAILURE MODES. , . . 3-8

3.6 FRONTAL VIEW OF FAILED MORTAR LAYER WITH NO CRACKS AT THE MOVABLE-FIXED BLOCK CONTACT . . . . . . . . . . . . 3-17

3.7 SCHEMATIC VIEW OF SHOTCRETE LAYER DEFLECTION AFTER SEPARATION STARTS . . . . . . . . . . . . . . . . . 3-17

3.8 MORTAR LAYERS FAILED BY SEPARATION OF MORTAR LAYER FROM THE SURFACE SLAB . . . . . . . . . . . . . . . . . . 3-19

3.9 STEEL PLATES PROVIDING RESTRAI NT TO ADHESION FAILURE PROPAGATION , · · , · · , · · · · · · · , · , · 3-19

3.10 TOP VIEW OF MORTAR CRACKING PATTERN IN TEST NO. 17 , 3-20

3.11 VERTICAL CRACKS IN THE MORTAR LAYER DUE TO BENDING STRESSES DEVELOPED BY LOAD ING PROCESS IN TEST NO. 16 · · • • , • · · 3-21

3.12 TOP VIEW OF ADHESION FAILURE DEVELOPED BETWEEN THE MORTAR LAYER AND THE CONCRETE SLAB COVERI NG THE MOVABLE BLOCK IN TEST NO. 15 · , · · · , · · , · · · · , · , , · · · , · · 3-22

3.13 MORTAR SURFACE CRACKS DEVELOPED ALONG PRE-LOADING WEAKNESS ZONES 3-22 . . . . . . . . . . . . . . . .. . . .. ..... ,

3.14 TYPICAL UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACE-MENT RELATIONSHIPS FOUND IN MORTAR LAYERS , , . , . . 3-24

3 .15 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST Ml & M2 , . . , , . , · , , , , , · , , · · , · , 3-28

3 .16 UNIT LENGTH RESISTANCE VS MOVABLE BLOC K DISPLACEMENTS TEST M3 & M4 , , , , , · , , , , , , , · , , , , , , ,

3.17 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST M5 & M6 , ....... , . , , , ..... , . ,

3.18 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST M7 & MS , , .. , , , · . , , , , , . , , , , , ,

3.19 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST M9 & Ml O . . . . . . . . , . . . . . , . , . . , ,

3.20 ,UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST Ml l & Ml 2 , . , . . . , . . . . , . . , . . . , ,

3.21 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST Ml 3 & Ml 4 . , , , · , , , , · , , , , , , , · , ·

3.22 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST f~l 5 & Ml 6 , . . , , , , . , . , , . . , . , , , ,

3.23 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS

.

.

• . 3-29

3-30

3-31

3-32

3-33

3-34

. ' 3-35

TEST Ml7 & Ml8 , ... , , , ... , ,··, , .. , , , . . . 3-36

X

3.24 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml 3-38

3.25 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M2 3-39


3.27 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M4 . 3-41


3.29 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M6 . 3-43



3.32 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Mll. 3-46

3.33 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml2. 3-47

3.34 FRONT FACE DISPLACEMENT OF LAYER W.R ,T. FLOOR: TEST Ml3(1) 3-48

3.35 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml4(1) , 3-49

3.36 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml5(1) . 3-50

3.37 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml6(1) 3-51

3.38 FRONT FACE DISPLACEMENT OF LAYER W.R.T, FLOOR: TEST Ml7(1) 3-52

3.39 FRONT FACE DISPLACEMENT OF LAYER W.R.T, FLOOR: TEST Ml8(1) .. 3-53

3.40 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR: TEST M13(2) .. 3-55

3.41 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR: TEST Ml4(2) .. 3-56

3.42 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR: TEST Ml5(2),.3-57


3.44 FRONT FACE DISPLACEMENT WITH RESPECT TO THE- FLOOR: TEST Ml7(2) .. 3-59


3.46 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER: TEST Ml & M2 .

3.47 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER: TEST M3 & M4 ..

xi

' . ' . ..3-63

.. 3-64

3.48 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST MS & M6 ...

3.49 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST M7 & M9 .. ,

3.50 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST Ml 1 & Ml 2 . .

3. 51 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST M13 & M14 ..

3.52 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST M15 & M16 ..

3. 53 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST M17 & M18 ..

3.54 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Ml ,M2 ,M7 & MB . . . . . . . . . . . . . . . . .

3.55 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Mll ,Ml2,Ml7 & Ml8 ............. , .

3.56 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Mll,Ml2,M13 & M14 ............. , .

3.57 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS M3 ,M7 & M9 . . . . . . . . . . . . . . . . . .

3.58 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Mll ,Ml2,M15 & Ml6 .............. .

3-65

3-66

I ~ I f 3-67

... , 3-68

3-69

3-70

3-74

3-76

3-78

3-80

3-81

4.1 FRONTAL VIEW OF TESTING DEVICE vJITH PLYWOOD WINGWALLS 4-3

4.2 CLOSE-UP SHOWING VERTICAL SCREED WIRES AND TAPES SURFACE .. , 4-3

4.3 FRONTAL VIEW OF COTTON-FILLED MOVABLE BLOCK-SURROUNDING SLOTS .....

4.4 GRADATION CURVES .

4.5 NOZZLE CLOSE-UP . .. 4.6 SCHEMATIC ARRANGEMENT OF THE SHOTCRETE EQUIPMENT

4.7 ARRANGEMENT OF SHOOTING EQUIPMENT .....

4.8 CLOSE-UP VIEW OF BELT CONVEYOR AND POWERED GUN

4.9 FIBER SCREENING USING 1-IN. (2.54 CM) SIZE SIEVE

. ' .

, . 4-4

4-7

4-9

, . 4-10

4-11

4-11

4-13

4. l O \>JARM-U P SHOO TI NG AGAINST PLYWOOD WALL . . . . . . . . . , . . . 4-13

Xii

4.11 STRENGTH-SPECIMENS PANEL BEING FILLED UP ... ' . .. , , , . 4-14

4.12 FINISHED STRENGTH-SPECIMENS PANEL . . . . . ' . ' . ' . 4.13 PATTERN OF SHOOTING , , ... , , •• ! ' • !I •• . ' ,

4.14 FRONTAL VIEW OF SHOTCRETE LAYERS IMMEDIATELY AFTER TRIMMING , . , ! • • , • • • , • , • • • , • , , • • I •

. , , 4-14

, . 4-15

, .. 4-18

4. 15 FRONTAL VIEW OF SHOTCRETE LAYERS DURING CURING PROCESS . , . , 4-18

4.16 COMBINED SHOTCRETE-SLAB SECTION AND CORRESPONDENT ADHESIVE TEST SAMPLES , . , ...... , . , . , .. , , . , , , , 4-24

4.17 ADHESIVE TEST SAMPLES AFTER TESTING ... ~ , ... , 4-24

4.18 ADHESIVE STRENGTH VS COMPRESSIVE STRENGTH OF THE SHOTCRETE LAYERS I I I I I , j t I .. I • I f I ~ I f p f ~ I t

4.19 FRONTAL VIEW OF FAILED SURFACES IN TEST NOS. l AND 2 , , , .. , 4-27

4.20 TYPICAL UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACE-MENTS RELATIONSHIP FOUND IN SHOTCRETE LAYERS , , , , . , . , . 4-30

4.21 UNIT LENGTH RE~ISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Sl & S2 , . . . . . , , , . . . . . , . , , , .

4.22 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S3 & S4 , . , . . . , . . . , . , . , . . . . . .

4.23 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S5 & S6 . . . . , . . . . . . . . . . . . . . .

4.24 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S7 & S8 . . . . . , , . , . . . . . . . , , , .

4.25 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S9 & Sl O . . . . . , , . , . . . . . . . . . , .

4.26 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Sl l & Sl 2 . . . . . . . . . . . . . . . . . . .

4.27 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Sl 3 & Sl 4 . , . , . . . . . . . . . . . . . , .

4. 28 UNIT LENGTH RESISTANCE VS f110VABLE BLOCK DISPLACEMENTS

.

.

•

.

.

•

•

.

.

. . 4-31

4-32

• . 4-33

. . 4-34

' . 4-35

. 4-36

' 4-37

TESTS Sl5 & Sl6 . , . , , , .... , . . . . . . . .. . 4-38

4.29 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl ... , ....... , .. , , . , 4-42

4.30 FRONT FACE DISPLACE~ENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST S2 .... , ... , . , .... , ..

4.31 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT

4-43

TO THE FLOOR TEST S3 ..... , ....... , . , . . 4-44

xiii

4.32 FRONT FACE DISPLAC81ENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST S4 ................. .

4.33 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST S5 ................. .



4.36 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST SB ............... , . ,

4. 37 FRONT FACE DISPLACEMENT OF SHOTCRETE LA-YER WITH RESPECT TO THE FLOOR TEST S9 ............. , ... ,

4.38 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST SlO ................ .

4.39 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sll ................ .

4.40 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl2

4.41 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl3 ............ , ... .

4.42 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl 4 . . . . . . . . . . . . . . . , .

4.43 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl5 ............... .

4.44 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S3 & S9 . . . . . . . . . . . . . , . . . . . .

4.45 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S4 & Sl O . . . . . . . . . . . . . . . . . . . .

4.46 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Sl , S2, Sl 3 & Sl 4 . . . . . . . . , . . . . . .

4.47 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S4, S6, SB & Sl2 ....... , ...... .

4.48 UNIT LENGTH RESISTA~CE VS MOVABLE BLOCK DISPLACEMENTS TESTS S4 & Sl6 .............. .

5.1 MAXIMUM RAM LOAD VS MEASURED ADHESIVE STRENGTH ..

5.2 BEAM MODELS USED IN RESIDUAL CAPACITY CALCULATIONS

.

.

.

B-2 ROUGHNESS MEASURING DEVICE .... ' .

. . .

'

. .

' .

.

4-45

4-'46

4-47

4-48

4 .. 49

4-50

4-51

4-52

4-53

4-54

4-55

4-56

4-62

4-63

4-66

4-71

4-73

5-2

5-4

B-2

B-2 TEST 1 (11/4/74) COLD ROLLED STEEL (VERY SMOOTH) . . . . B-3 xiv

l

B-3

B-4

. C-1

C-2

TEST 1 (11/12/74) MID-NORTH FINISHED SIDE

TEST 3 (11/11/74) SOUTH TOP FORM SIDE ..

FRONT VIEW OF THE TESTING DEVICE AND MONITORING SYSTEM

SAMPLE ATTACHING SCHEME AND GAGE MEASURING STRAIN ACROSS THE CONTACT ........ .

B-4

B-5

C-2

C-2

C-3 FAILED ADHESIVE TEST SAMPLE ................ C-3

C-4 LOAD VS CONTACT DISPLACEMENTS RELATIONSHIP OBTAINED FROM ADHESIVE TESTS SlO .................... C-9

C-5 LOAD VS CONTACT DISPLACEMENTS RELATIONSHIP OBTAINED FROM ADHESIVE TESTS S9, .................. . C-1O

xv

•

•

CHAPTER l

INTRODUCTION

A device was constructed to study and test the structural behavior

of thin shotcrete linings under load in a configuration that simulates

loosening behavior in a jointed rock tunnel. In the first series of tests

the thin shotcrete lining was replaced by a sand-cement mortar layer which

was troweled onto the surface of the testing device. These tests were used

to evaluate the performance of the testing apparatus and the modes of failure

and performance of a material having properties similar to shotcrete. A

second series of tests were conducted on shotcrete which was applied to

the surface of the model in the same manner used for placing shotcrete under

ground. In these tests the major variables that influence the support capac

ity of a thin shotcrete lining in a plane configuration were investigated;

the results of these tests, application of the shotcrete, and performance

of the test device will be described herein.

The ultimate objective of this testing program is to develop a

more rational procedure for the design of the thin shotcrete linings used

as support in tunnels driven through jointed rock. One means of develop

ing such procedures is to study the structural behavior of thin linings

using physical models which represent actual conditions encountered in

tunnels. The approach emp loyed in this project was to perform a series

of structural load tests in which parameters of shotcrete and pertinent

geology were methodicall y varied while keeping the configura tion of the

tunnel surface constant. As it was impractical to perform enough tests

l - l

to cover the full range of variables, procedures to predict the struc

tural behavior of a lining subject to untested conditions were developed,

based on the results obtained from the tests. These procedures, involving

simple hand calculations as well as computer analyses using finite element

methods, will make possible the construction of design charts to be used

for est imating the maximum load that a given lining could support in a

given set of field conditions.

Two types of variables were studied in the determination of the

load-deformation characteristics of the thin shotcrete linings. Geological

va ri ables included (1) the nature of rock surface as it affects adhesion be

tween the shotcrete and the rock and (2) the boundary conditions of the

shotcrete layer . Other geological variables such as ftlJing of joints and

filling of shotcrete between their surfaces were not studj ed. The second

type of variable involved the strength and deformability of the shotcrete;

they were varied by changing the thickness, time of curing, and type of

reinforcement. The proportion: of the materials used in the shotcrete mix

were kept constant for all the tests.

Typical geometric configurat ion that has been observed in tunnels

driven through flat-lying sedimentary rocks, r oc ks containing horizontal

stress relief joints and flat-roofed openings in jointed rock are shown

schematically in Fig. l .l. Sketches of actual tunnels having a similar

geometry are shown in Fig. 1.2. In actual tunnels, there are a very large

number of possible rock block geometries as well as variations in the rela

tive sizes of the blocks. This last variable however could be standardized

usin g a suitable scaling factor.

l -2

'

(a) (b)

FIGURE 1. 1 TYPICAL GEOMETRIC CONFIGURATIONS AND LOADING CONDITIONS IN TUNNELS INTERSECTED BY FLAT-LYING DISCONTINUITIES OR IN FLAT-ROOFED OPENINGS IN JOINTED ROCK

1-3

FIGURE l .2 FIELD EXAMPLES OF TUNNELING IN 11 BLOCKY 11 RCCK MASSES

(Craig, C. L. and Brockman, L. R., 1971)

1-4

t.

A testing device was designed to simulate the flat-roof condition

yet have the versatility to model other geometric configurat ions (Fig. 1.3).

The model was set up so that ·a con tinuous record of the l ining loads and

deformations was obtained throughout the tests. The forc e on the shotcrete

Fixed block Movable block

Hydraulic ram

Fixed bl ock

Shotcrete

FIGURE 1.3 PLANAR GEOMETRY OF TEST DEVICE FOR STRUCTURAL TESTS ON SHOTCRETE LAY ERS

lining was applied using hydraulic rams so that loads could be controlled

and measured accurately. The rams selected for use on this project are

controlled electronically to provide either load or de formation rate control.

When combined with incremental loadin g, this system allows observation of

lining behavior at various load level s.

A system of reinforced concrete blocks was dev i sed to simulate

the basic tunnel geometry (Fig. 1. 3). A movable block was at t ached to a

hydraulic ram to represent a roc k block as it applies load t o a thin shot

crete lining. Adjacent fixed bl ocks simulated the sta t ionary rock mass

within the tunnel. The fixed bloc ks were attached to the labora t ory test

floor with prestressed rods. The model was set up so that the movable block

was pushed horizontally r ather than falling downward as woul d take place in

1-5

a tunnel. This adjustment avoided some problems associated with the dead

weight of the block, allowed the test device to be secured to the laboratory

floor more easily, and provided a more convenient test surface for placing

the shotcrete. In addition, it reduced danger from spalling of shotcrete

during testing while measurements were being made. In the original design

of the loading system only one movable block was provided, but it became

apparent that preparation for placing the shotcrete for each test would be

so extensive that it would be desirable to have at least two structural tests

for each shooting. Therefore, a second movable block was added below the

first. This arrangement also provided a means for checking possible varia

tions in shotcrete properties and behavior associated with shotcrete ap

plication by performing two identical tests on shotcrete applied at the

same time.

In order to study the effects of surface adhesion, and to provide

various surfaces that are typical of the tunnel environment, provisions were

made for changing the surface of the fixed and movable blocks. This was

accomplished by bolting 3 in. (7.62 cm) thick mesh-reinforced concrete

slabs to the fixed and movable blocks. The surface roughness of these

slabs was varied to simulate different joint surfaces. The shotcrete was

applied directly to these slabs.

In the next chapter the test device is described in greater de

tail. Chapter 3 outlines the test program and the results obtained from

the preliminary mortar tests. The characteristics and results obtained

from the structural tests on thin shotcrete linings in a planar configur

ation are described in Chapter 4. Finally, in Chapter 5, the conclusions

and recommendations drawn from the testing program are presented.

1-6

Geometric configurations other than a planar surface will be

studied and tested in future work (Fig. 1.4). These configurations will

be obtained by replacing the existing blocks or adding new sections with

different shapes. The movable blocks, load arrangement and test proce

dures will remain essentially the same. These tests will be used to de

velop design criteria for thin shotcrete linings and a large range of

geologic conditions.

Fixed block Movable block

Shotcrete

Hydraulic ram

Fixed block

e1 and e2 are variable

Fixed block Movable b 1 ock

Hydraulic ram

Fixed block

FIGURE 1.4 FUTURE SHOTCRETE TESTS INVOLVING OTHER ROC K GEOMETRIES

1-7

CHAPTER 2

DESCRIPTION OF TEST DEVICE

A testing scheme, versatile enough to be adapted to the variation

of the chosen parameters, was designed. This scheme is shown in the photo

graph of Fig. 2.1 and consists of (l) the reaction abutment on the left,

which remains unaltered from test to test; (2) the test wall on the right

with fixed and movable portions, the front surfaces of which are covered

with the thin shotcrete layer; and (3) the two hydraulic rams, which thrust

against the reaction abutment to apply load to the movable portion of the

wall. The test device and instrumentation are further described in the fol

lowing sections.

2.1 REACTION ABUTMENT

The reaction abutment shown in Fig. 2.2 acted as a reaction to

the force applied through the rams to the thin shotcrete layers. It was

attached to the floor of the test area by three steel bolts that were pre

stressed to 50 kips (220 kilonewtons). The abutment was similar to those

employed as reactions for the forces applied during the testing of cylin

drical liners previously performed in the University of Illinois laboratory

(Parker, et al., 1973). Successful performance of the abutment during the

previous tests, which required loads equal or greater than those applied

in this test program indicated that the abutment would perform adequately.

2-1

FIGURE 2.1 OVERALL VIEW OF THE TESTING DEVICE

FIGURE 2.2 DETAIL OF RAMS-ABUTMENT CONNECTION

2-2

2.2 HYDRAULIC RAMS

Two MTS hydraulic rams, shown in Fig. 2.3, each 85 in. (216 cm)

long with a 5-in. (12.7-cm) stroke and able to apply a maximum load of

100 kips (440 kilonewtons) in either tension or compression were used in

these tests. Each loading unit consisted of the ram and its valve system,

a load cell, and a ball and socket seating arrangement at the connection

between the movable block and the loading unit. Details of the basic

structure of the ram and its characteristics are given in Appendix A.

The rams were located 21 in. (53.3 cm) and 48 in. (122 cm) above the floor,

and were leveled and aligned so that the axial thrust would be perpendicu-

lar to the wall. They were bolted to a steel plate embedded in the con-

crete abutment. A steel frame providing intermediate support for the rams

was located 36 in. (91.4 cm) from the reaction abutment as shown in Fig.

2.3. These supports were used to set and maintain the vertical and hori

zontal alignment of the loading unit. The load in the rams was transmitted

to the movable blocks through al in. (2.54 cm) spherical steel seat at the

end of the rams and the movable blocks (Fig. 2.4). The sphere was used to

transfer the loads so that moments would not be induced in the movable blocks.

The rams were controlled electronically to provide a predeter

mined rate of loading or rate of displacement of the movable block. This

control allowed the simulation of different types of loading on the shot

crete specimen. It was also possible to stop the displacement or load

application at any desired load level and maintain that level for any time

span. Thus, the test can be performed continuously, or in increments,

2-3

' FIGURE 2.3 STEEL FRAME ASSURING VERTICAL AND HORIZONTAL

ALIGNMENT OF THE RAMS

FIGURE 2.4 DETAIL VIEW OF RAM-MOVABLE BLOCK CONNECTION

2-4

allowing the behavio r of the shotcrete to be investigated at any stage

during the test. The rate of loading, or displacement, was controlled by

electronic regulation of the hydraulic flow into the rams . The load

deformation output of the rams was monitored with an x-y recorder.

2.3 FIXED WALL AND MOVABLE BLOCKS

The wall on which the shotcrete layer was applied is 10 ft (305

cm) long and 6 ft 6 in. (198 cm) high. Two 2 x 2 ft (61.0 x 61 .0 cm) mov

able blocks, one above the other, were located in the middle of the wall.

The back of this wall is shown in the photograph of Fig. 2.1. A front

view of the wall illustrating the relative position of the concrete blocks

comprising the test model is shown in Fig. 2.5. A photograph of this same

frontal view is presen ted in Fig. 2.6. The fixed blocks were held to the

test floor with four vertical bolts extending through the entire wall.

These bolts were prestressed to 25 kips (110 kilonewtons) thereby producing

a rigid structure on which the shotcrete was placed. During some early

tests the blocks of concrete were not grouted to the floor. Early tests

were also conducted using only one movable block. To increas e the stiff

ness of the model and the number of tests that could be conducted from a

single shotcrete application, an extra movable block was added and the con

crete blocks were grouted to the floor . In order to provide the desired

bonding conditions without replacing the fixed or movable blocks, precast

facing slabs were placed on the front or the wall. These slabs were 3 in.

(7.62 cm) thick and were bolted and grouted to both the fixed and movable

blocks.

2-5

Test floor 1•

II 11 11 II

" 11 11 ,, ,, 11 II II II ,, ,, II II II

1/2 11 Steel plates

,. I 611

-..tJ

6"

6" , 6"

10 1 -0 11

Movable block

4 1 -0 11

Hold-down bolts

l -1/2 1

5'

~ 6"

L 6"

2 ':..Q" 6"

6"r

111 - 2 1 -0 11

I' ,. I Scale

FIGURE 2.5 DIMENSIONS OF SURFACE SLAB AND HOLE PATTERNS FOR ATTACHING THEM

2-6

FIGURE 2.6 FRONT FACE OF THE FIXED WALL

The fixed walls were used in this model to simulate a stable rock

mass in a tunnel roof or wall. They were constructed of reinforced concrete

and were provided with horizontal holes for attachmen t of the surface slabs.

Concrete with a nominal 5000 psi (350 kg/cm2) compressive strength and

obtained from a local ready mix plant was used. The forms and reinforce

ment for the fixed blocks are shown in Fig . 2.7. A similar form was used

for the long concrete block placed across the top of the model (Fig. 2.5).

The reinforcing bar cage shown in Fig. 2.7 consisted of No. 3 and No. 6

deformed bars; the larger diameter vertical bars being placed 1 in. (2.54 cm)

2-7

FIGURE 2.7 FORMS AND REINFORCEMENT FOR THE FIXED SIDE BLOCKS

from the fr ont face of the blocks where the compression stresses due to

forward bending of the walls would be high. The pres tressing bolts used

to attach the fixed blocks and transverse beam to the test floor were placed

through two, 2.5 in. (6.35 cm) diameter pipes in each block. Eight steel

pipes, l in. (2.54 cm) 0.D., were placed l ft (30.5 cm) apart in two rows

for attachment of the surface slabs. A steel plate 5 ft (150 cm) by l ft

(30.5 cm) by 1/2 in. (1.27 cm) thick was cast into the fixed walls adja

cent to the movable blocks . A fr ont view of this plate is show in Fig. 2.5.

2-8

The lower movable block and its connection with the rams was

supported on a concrete base block (Fig. 2.5). The base support block

was 9 in. (22.9 cm) tall, with dimensions of 2 ft (61.0 cm) by l ft (30.5

cm) and was lightly reinforced. This block was grouted to the floor and

its surfaceleveled. Both movable concrete blocks rested on a ball and

groove arrangement like those shown in Fig. 2.6. This device served to

guide the movable blocks and minimize the friction between them and their

support. The upper one rested on a steel support bolted to the plates

located on sides of the fixed walls (Fig. 2.5). A ball and groove guide

was also employed at the top of each movable block. This served to pre

vent the blocks from tilting forward or backward. The movable blocks 2 ft

x 2 ft x l ft (61.0 cm x 61.0 cm x 30.5 cm) were cast in the form shown in

Fig. 2.8. In this figure the reinforcing cage, which consisted of No. 6

deformed bars, can also be seen.

The surface slabs were attached to each block by four, 1/4 in.

(0.635 cm) diameter steel rods which were threaded into nuts cast in the

slabs and were bolted on the back side of the blocks. The forms for the

surface slabs were made of steel so that deflections from the wet concrete

would be minimized and maximum reusability would be assured. One of these

forms including the mesh reinforcement and threaded inserts for the attach

ing bars is shown in Fig. 2.9.

2.4 INSTRUMENTATION

Two basic types of deformation measurements were made in the

mortar tests; the displacement of the mortar layer with respect to the

2-9

FIGURE 2.8 FORM AND REINFORCEMENT FOR THE MOVABLE BLOCKS

FIGURE 2.9 FORMS, MESH REINFORCEMENT AND THREADED INSERTS FOR SURFACE SLABS

2- l 0

fixed walls and the floor, and the strains occurring in the mortar layer.

The last set of measurements was discontinued in the shotcrete tests.

Displacement measurements were made with dial gages having sen

sitivities of 0.001 and 0.0001 in. (2.54 x 10-3 cm) and (2.54 x 10-4 cm).

These gages were attached to a steel frame which was bolted to the floor

(Fig. 2.10). These dial gages, located 10 in. (25.4 cm) apart on a hori

zontal line at the midheight of the mortar or shotcrete layer, were used

to measure the relative displacement of the layer with respect to the floor.

Because of irregularities in the layer surface, and to avoid damage of the

dial gages after failure of the shotcrete, the gages were not in direct

contact with the layer; the contact was made through steel plates pre

viously grouted to the surface, as shown in Fig. 2.11. Three dial gages

were mounted on the back of the movable block (Fig. 2.4) such that their

plunger could bear directly against the back of the fixed block. These

gages were used to monitor the relative horizontal displacement between

the movable block and the fixed walls. The triangular arrangement of

these gages also provided a means for detecting any tilting of the movable

block caused by eccentric loading or non-uniform resistance of the mortar

layer. Another set of dial gages recorded the displacements of the back

of the fixed walls with respect to the laboratory floor. These gages, as

shown in Fig. 2. 11, were located at different distances from the movable

blocks and at different elevations relative to the floor in order to de

tect any rotation of the walls that might occur during the loading process.

During the initial tests a Whittemore gage was used to measure

the relative displacement of points located 10 in. (25.4 cm) apart on a

2-11

FIGURE 2.10 FRONTAL DIAL GAGES AND STEEL FRAME SUPPORTING THEM

FIGURE 2. 11 MORTAR SURFACE-DIAL GAGE BRACKET CONNECTION

2-12

horizontal line at midheight on the outer surface of the mortar layers.

Most of these Whittemore points were located on the same steel bearing

plates that were used as surface reference points for the dial gages.

The loading was performed incrementally, with dial gage and Whittemore

readings taken at the end of each increment. After each load increment,

up to the peak, the load was maintained constant while the readings were

taken. After the resistance of the layer started to decrease, the test

ing procedure was changed. For some tests the constant rate of loading

was continued until failure of the layer, without stopping for additional

measurements. For most tests, however, the loading was changed to a con

stant strain rate, and controlled such that readings could be taken at pre

determined deformation increments to determine the full load-deflection

curve for the mortar or shotcrete layer.

2-13

CHAPTER 3

PREL.IMINARY TESTING PROGRAM

A preliminary investigation using sand-cement mortar as a sub

stitute for shotcrete was carried out to determine the performance of the

test device, to assess the main variables influencing the mode of failure

of thin linings, and finally, to check the repeatability of test results.

3.1 PREPARATION OF THE SPECIMENS

In all tests, the mortar of the thin layer consisted of the same

mix design. Water, sand and cement were mixed in 260 lb (118 kgms) batches

in a rotatory, pan-type mixer. Table 3.1 shows the amounts and relative

percentages of the three mix components. The water/cement ratio of the

mix was 0.54 and 0.52. In all of the tests approximately l in. (2.54 cm)

TABLE 3.1

MORTAR COMPONENTS IN 260 LB (118 kgm) BATCH

Mix components Weight Percentage of the lb (kgms) total mix

Cement 65 (29.5) 25.0

Sand 160 (72.6) 61.5

Water, tests 1-4 35 (15.9) 13.5

tests 5-18 34 (15.5)

of mortar was placed on the fixed and movable blocks. A thin layer about

3-1

1/2 in. (1.25 cm) was applied, first, with a trowel, and the remainder

placed approximately 1/2 hr later using the same procedure . This two

stage appli cation was used to avoid sloughing of the mortar layer which

occurred when it was placed in one application. The mortar layer was

cured by cover ing it with wetted burlap which hung down the front of the

wall. The bur lap was continuously wetted during the curing period until

the specimen was ready to be tested. This procedure was intended to simu

late the high humidity typically found in underground openings. Control

specimens werecast to determine the approximate strength characteristics

of the layer material and were cured in a fog room. In test Nos. l to 4,

cracks were observed on the exposed surface of the mortar layer at the end

of the curing period (Fig. 3.1). These cracks were beli eved to be the re

sult of sloughing of the second layer of mortar rather than by shrinkage

of the material. Pre-test cracks were not present in the remainin g

tests where the water content of the mortar was slightly reduced, and

greater pressure was used in applying the mortar to the wal l. Figure 3.2

shows the front faces of test Nos. 5 and 6 which were typical of the mor

tar layers havin g a reduced water/cement ratio. The appa rent irregularities

· on the layer surface were traces left by the trowel during the placement of

the mortar.

3.2 GEOMETRY AND BOUNDARY CONDITIONS OF TESTS

In al l of the tests, the movable block slab surface was in the

same vertica l plane as the front face slabs of the fixed blocks before the

mortar was placed. Therefore the resistance of the layer to the force

3-2

FIGURE 3.1 PRE-TEST SURFACE CRACKS IN TEST NO. l

FIGURE 3.2 APPEARANCE OF SPECIMEN NOS. 5 and 6 IMMEDIATELY BEFORE TESTING

3-3

applied through the movable block could be developed only by the trans

mission of shear and/or adhesive stresses through the mortar layer. The

top and bottom-edges of the mortar layer were aligned with the top and

bottom edges of the movable block. This ensured a one-directional trans

mission of stresses and avoided stress concentrations around sharp geometri

cal transitions.

For the first 10 tests, no restrictions were imposed on the lat

eral boundaries of the layer, and the boundary was provided by the adhesion

strength along the contact of the mortar layer and the concrete surface

slabs of the fixed blocks. For test Nos. 11 to 18, steel plates were used

to press the mortar layer against the fixed walls at specified distances

from the movable block. Lateral boundary conditions were semi-fixed by

the steel plates in these tests. These plates can be seen in Figs . 3.3

and 3.4.

For all tests, except the first two, wetted cotton was used to

fill the 1/2 in. (1.27 cm) gap between the movable block surface slab and

the surrounding surfaces. Filling of this separation presented possible

intrusion of mortar which would result in frictional resistance between

the movable block and fixed wall.

3.3 MAIN VARIABLES AFFECTING THE STRUCTURAL BEHAVIOR OF THE MORTAR LAYER

Once the geometrical condition of the tests was chosen, a set

of layer and "rock-mass" characteristics, which would influence the struc

tural behavior of the layer, were selected and are summarized in Table 3.2.

For a series of tests, different values were given to the particular

3-4

FIGURE 3.3 USE OF 6 X 18 IN. (152 X 457 MM) PLATES IN TEST NOS. 13 AND 14 TO SIMULATE ROCK BOLTING

FIGURE 3.4 USE OF 16 X 24 IN. (406 X 609 MM) PLATES IN TEST NOS. 17 AND 18 TO SIMULATE ROCK BOLTING

3-5

TABLE 3.2

DIMENSIONS OF t,ORTAR LAYER

Test Thickness, no. in. (cm) L*,in. (cm) Remarks

l 1. l (2.79) 24 (60.96)

2 .9 (2.29) 48 (121.92)

3 1.0 (2.54) 48 ( 121. 92)

4 .7 (1. 78) 7 (17 .78)

5 .7 (1. 78) 48 ( 121. 92)

6 48 ( 121. 92)

7 1. l (2.79} 14 (35.56) /

8 .9 (2.29) 18 (45.72)

9 .7 ( 1. 78) 48 (121.92)

10 .8 (2.03) 48 (121.92)

11 .6 ( 1. 52) 6 (15.24) Steel plates 611 x 18 11

12 .6 1.52 6 (15.24) Steel plates 611 x 18 11

13 .7 (1. 78) 6 (15.24) Steel plates 611 x 18 11

(used tape on slabs)

14 .6 ( l . 52 6 (15.24) Steel plates 611 x 18 11

(used tape on slabs)

15 1. l (2.79} 6 (15.24) Steel plates 611 x 18 11

(Mesh reinforcement)

16 1.0 (2.54) 6 (15.24) Steel plates 611 x 18 11

(Mesh reinforcement)

17 .7 ( 1. 79) 2 (5.04) Steel plates 16 11 X 24 11

18 .8 (2.03) 2 (5.04) Steel plates 16 11 X 24 11

* Distance between the edges of the movable block and the lateral boundaries of the layer.

3-6

characteristic under study while the values of the other p?rameters were

kept constant. Differences in the mode of failure and maximum resistance

loads obtained in these tests were used to assess the influence of that

particular property on the overall behavior of the structure.

After a theoretical analysis complemented with a study of the

available literature on shotcrete behavior (Cecil, 1972; Peck, et al.,

1970; Cording, 1974; Cording and Mahar, 1974; Jones and Mahar, 1974; and

Holmgren, 1975) was made, a hypothesis was developed to explain the possi

ble failure mechanisms and the main variables as shown in Fig. 3.5. The

maximum load resisted by the mortar layer depends on its mode of failure.

There were two basic modes of failure predicted for this test series:

(1) diagonal tension failure in the mortar layer; or (2) separation of the

mortar layer from the surface slab. The actual mode of failure depends

on the relative value of the forces F0 and F1, where F0 is the maximum ad

hesive force holding the mortar layer against the fixed walls that could

be developed along the contact area, and F1 is the force required to in

duce a diagonal tension failure in the mortar layer. If F0 is greater than

F1 the first mode of failure, diagonal tension, will occur or, conversely,

if F1 is greater than F0, the second mode of failure, separation of the

mortar layer, will occur. As seen in the diagram the value of F0 depends

on the size of the contact area along which adhesive stresses act together

with the maximum value of adhesive strength between the layer and the slab,

while ~he values of F1 depend on the thickness of the layer together with

the strength of the mortar. It was decided, therefore, to study the in

fluence of these variables on the values of F0 and F1• The variables

3-7

)

-

---

-

-

w I

CX)

Layer thickness

Strength

Surface conditions

Lateral ~ boundary conditions

,, . Strengt

Fl [. ~ - .k I F0 > F1 Diagonal tension failure

I \ Fl >Fa Adhesive failure

Fa [ ~;;~ ~ .

FIGURE 3.5 SCHEMATIC DIAGRAM SHOWING TWO TYPES OF FAILURE MODES

chosen in this study consisted of: (l) lateral boundary conditions of the

layer; (2) the contact surface characteristics; (3) the mortar strength;

(4) the type of reinforcement ' used in the layer; and (5) rate of load ap

plication to the mortar layer.

The mortar layer thickness was intended to be constant throughout

the test series but could not be closely controlled due to the application

method. For each test its value was measured and recorded along the two

critical sections of the layer; between the fixed and movable blocks.

It was believed that the structural behavior of shotcrete layers

is similarly influenced by t he same variables aforementioned, so that the

results of these mortar layer tests were useful in planning the testing pro

gram for the shotcrete layers. The nature of these variables and the dif

ferent values assigned to them during the eighteen tests performed in this

preliminary study are described in the following sections.

3.3.1 LATERAL BOUNDARY CONDITIONS OF THE LAYER

In the cases where no steel plates were used, the lateral boundary

of the mortar layers was determined by its maximum distance away from the

movable block. For the other cases, when a good contact between the steel

plates and the mortar was obtained, the location of these plates determined

the lateral boundaries of the layer. Column 3 in Table 3.2 shows the dis

tance from the contact between the movable and fixed blocks at which the

lateral boundaries of the layer were located . Column 5 of the same table

indicates whether or not steel plates were used to establish these boundaries.

As shown in the aforement i oned table a considerable range of variation, 2 in.

3-9

'

(5.08 cm) to 48 in. (122 cm) was selected for the locations of the lateral

boundaries of the layers. The location of these boundaries was expected

to influence the structural behavior of the layers in as much as this loca

tion controlled the size of the area over which the adhesive strength be

tween the mortar and the surface slab was developed. Even if the adhesive

strength developed within just a few inches of the movable-fixed block con

tact, longer extensions of the mortar layer would have provided a larger

"buffering" zone should shrinkage in the mortar layer have had adverse

effects on the development of the adhesive strength. Shrinkage in the mor

tar (layer) tended to create shear-strains along its contact with the sur

face slab reducing ~nd sometimes destroying any adhesive strength which

could have developed. Longer extensions of the layer were also expected

to provide better restraints to rotations induced in the layer after separa

tion from the surface slabs was started.

3.3.2 CONTACT SURFACE CHARACTERISTICS

Slab surface conditions along the contact area determined to a

major degree the maximum value of the adhesive strength that developed to

hold the mortar layer to the fixed wall when load was transmitted to the

layer through the movable block. As previously mentioned, the maximum value

of the adhesive strength that could be developed along the contact area to

gether with the effective size of this area determined the maximum value of

the force F0 and , therefore, the structural behavior of the layer.

In order to maintain a uniform surface condition for each test,

and particularly for successive tests in which adhesion was not a variable,

3-10

a standard surface treatment was established. After brushing the slab

with an electrically powered wire brush, the roughness of the slab surface

was measured at representative locations with a special device designed

for this purpose. The device and results of the measurements are described

in Appendix B. Mortar was placed after the roughness was measured.

The surface slabs were form-finished on one side and hand troweled

on the other. For most of the tests, the mortar was placed against the

finished side of the slab after it had been roughened. Variations of the

maximum adhesive strength were provided by (1) the use of the rougher,

hand troweled side of the surface slab as the contact surface in the first

two tests or (2) by covering the inner edges of the fixed block with a fila

ment tape in a strip 6 in. (15.2 cm) wide (see test Nos. 13 and 14).

3.3.3 MORTAR STRENGTH

Variations in the strength characteristics were obtained by al

lowing the mortar layer to cure under the same conditions for different

lengths of time. Material properties of the mortar in each test are sum

marized in Table 3.3.

The strength of each mortar layer was estimated by performing

a series of standard compressive and flexural strength tests on cast sam

ples of mortar obtained from each mix and cured under similar conditions

as the mortar on the wall. These strength tests were conducted at the same

time 'as testing of the mortar layer in the model and were used to check dif

ferences in strengths between mortar layers cured for approximately the same

length of time (strength control). Four cylinders 4 in. x 8 in. (10.2 cm x

3-11

'

TABLE 3.3

MATERIAL PROPERTIES OF TEST SPECIMENS

Splitting Compressive Flexural tensile

strength, strength, strength, Young's

Test f' fr, f sp, modulus c' psixl06 no. psi (KP a) psi ( KP a) psi ( KP a) ( KP a) hours

1 6015 ( 41 ,400) 2.5 (1.72 X 107) 168

2 5540 (38,200) 640 (4,410) 168

3 1965 (13,550) 387 (2,670) 48

4 5925 (40,800) 510 (3,510) 450 (3,100) 168

5 5186 (35,800) 660 (4,550) 505 (3,480) 3.0 (1.72 X 107) 168

6 5186 (35,800) 660 (4,550) 505 (3,480) 3.0 (2.07 X 107) 168

7 4775 (32,900) 430 (2,960) 360 (2,480) 2.8 ( 1. 93 X 107) 168

8 4775 ( 32,900) 430 (2,960) 360 (2,480) 2.8 (1.93 X 107) 168

9 385 ( 2,660) 60 413) 0.3 (2.07 X 106) 7

10 385 ( 2,650) 60 413) 0.3 (2. 07 X 106) 7

11 5090 (35,100) 510 (3,520) 410 (2,830) 2.2 (1.52 X 107) 168

12 5090 (35,100) 510 (3,520) 410 (2,830) 2.2 (1.52 X 107) 168

13 5390 (37,200) 585 (4,030) 440 (3,040) 3.7 (2.55 X 107) 168

14 5390 (37,200) 585 (4,030) 440 (3,040) 3.7 (2.55 X 107) 168

15 5630 (38,800) 415 (2,860) 3.2 (2.21 X 107) 168

16 5630 (38,800) 415 (2,860) 3.2 (2.21 X 107) 168

(35,100) 2.2 7 168 17 5090 480 ( 1. 52 X 10 )

18 5090 (35,100) 480 2.2 (1.52 X 107) 168

3-12

• '

20.3 cm), and two rectangular beams 6 in. x 6 in. x 22 in. (15.2 cm x 15.2

cm x 55.9 cm) were tested from each batch. Standard unconfined compres

sion tests were performed on two or three of the cylinders and Brazil

splitting tensile tests were conducted on the remaining cylinders. In

the compression tests load deformations curves were obtained, and were

used to calculate Young's Modulus; see column 5 of Table 3.3.

3.3.4 TYPE OF REINFORCEMENT

In order to investigate the influence of the mortar layer stiff

ness and ductility on its structural behavior, particularly after cracking

in the layer occurred, two of the mortar layers tested were reinforced

with mesh. The reinforcing mesh used in test Nos. 15 and 16 had al in.

(2.54 cm) square pattern, formed with a 0.063 in. (1.06 mm) diameter wire

and was placed close to the outside surface of the layer. The mesh was

pushed against a fresh mortar layer and covered immediately thereafter with

the second layer. The reinforced mortar layer was held against the fixed

walls with a set of steel plates similar to those shown in Fig. 3.3 but

were located 3 ft (91.4 cm) rather than l ft (30.4 cm) away from the mova

ble block.

3.3.5 RATE OF LOAD APPLICATION

It is reasonable to assume from a structural point of view that

the rate at which the load is applied to the layer will have an influence

on the numerical value of forces F0 and F1 in the aforementioned model.

From the geological point of view, the rate of load application is a very

3-13

1

important variable directly related to the 11 stand-up 11 time of the material

surrounding the tunnel . Since the 11 stand-up 11 time of rock in blocky ground

is highly variable, it was decided to run comparative tests at two extreme

rates of loading.

For all the tests except 8 and 10, a 11 slow 11 rate of loading equal

to 2 lbs/sec (8.9 x ,o-3 kN/sec) was used. For test Nos. 8 and 10, the

load was applied rapidly to simulate the instantaneous development of load

on the layer imposed by a rock block whose gravity load was mobilized quick

ly and whose weight exceeded the support capacity of the layer .

3.3.6 THICKNESS OF THE MORTAR LAYER /

For this series of preliminary tests the mortar layer was intended

to have a uniform thickness of 1 in. (2.54 cm). However, due to the place

ment method, it was not possible to control this thickness accurately over

the entire area of the layer. Column 2 in Table 3.2 indicates the average

thickness of the mortar layers obtained from several measurements taken

along the failure planes of the layer.

3.4 LOADING PROCEDURE

Results obtained from the first several tests indicated that it

was pertinent to study the structural behavior of the mortar layer after

the load reached a value equal to the maximum resistance of the layer. For

the first tests, Nos. l through 11, the loading process was performed en

tirely under load control. The electrically controlled ram was set to apply

a maximum load of 10,000 lbs (44.48 kN) over an interval of 5000 sec. The

3-14

maximum displacement for the ram head (1/2 in.) was controlled by attach

ing an electrical contact switch to the dial gage monitoring the displace

ment of the center point of the mortar layer. Once the displ acement reached

1/2 in. (1.27 cm) a contact was made cutting the load immediate ly to zero.

For the other series of tests, Nos. 12 through 18, the loading

proceeded up to a maximum capacity of the layer under load control. Once

this value was reached, however, the load in the ram was immediately cut

off manually and the displacement of the ram head stopped. A small load,

however, due to the back-up pressure in the hydraulic seals remained in the

ram. Further displacements of the ram head were controlled in such a way

that it applied whatever load necessary to advance at a pre-determined dis

placement rate of 0.0025 in./sec (displacement control). Use of this pro

cedure permitted study of the behavior of the layer and measurement of the

resulting loads and displacements once the maximum capacity of the mortar

was reached.

3.5 TEST RESULTS

With the exceptions of test Nos. 5 and 6, no special difficulties

were encountered in testing the mortar layers. Observations and measure

ments in each test were carried out as previously described and no major

equipment or testing problems were encountered. Non-controlla ble, non

measured loads imposed in the mortar layer during ram head alignment for

test Nos. 5 and 6 created a premature separation of the mortar layer from

the surface slab. Results obtained from these tests were plotted but not

used in comparisons with other test results.

3-15

3.5.l MODES OF FAILURE

Of the two basic modes of failure proposed in themodel of Chapter

3, only separation between the mortar layer and the concrete surface slab

was observed in these preliminary tests. The continuous displacement of

the movable block, induced by the load in the ram, produced adhesion stress

in the contact area between the mortar layer and the surface slabs as well

as tension and compression stresses in the mortar layer itself. It was

observed, however, that in all cases the induced adhesion stresses exceeded

the adhesion strength at the contact area before the level of stress in the

layer reached the strength of the mortar. A separation of the mortar layer

from the surface slab started at the movable block and progressed away from

it toward the outer boundaries of the layer. Variations in the structural

behavior of the mortar layer after separation from the surface slab were

observed in different tests. In one case, test No. 4, the size of the con

tact area beyond the movable block was so small that the adhesion failure

occurred almost simultaneously along its length and the layer moved as a

rigid body uniformly outward with the movable block. Figure 3.6 shows a

frontal view of the failed mortar layer; the fact that cracking did not

occur in the mortar layer indicated that the magnitude of the stress in

duced in the layer never exceeded the flexural strength of the mortar.

In most of the cases, the mortar layer, after its initial separa

tion from the surface slab, started acting like a simply supported beam

having a uniformly loaded center section and end supports which continuously

moved apart (see Fig. 3.7). When the separation between the mortar layer

3-16

'

FIGURE 3.6 FRONTAL VIEW OF FAILED MORTAR LAYER WITH NO CRACKS AT THE MOVABLE-FIXED BLOCK CO NTACT

p

FIGURE 3.7 SCHEMATIC VIEW OF SHOTCRETE LAYER DEFLECTION AFTER SEPARATION STARTS

3-17

and the surface slab became long enough, the bending stresses in the layer

exceeded its flexural capacity and two ve r tical cracks appeared in the mor

tar along the contact be tween the movable and fixed blocks. The progres

sive separation of the mortar layer occurred so fast that the cracks ap

peared almost simultaneous ly with the adhesion failure.

In some cases, when steel restraining plates were not placed at

the boundaries of the layer, t he separation of the mortar layer f r om the

surface slab propagated all t he way to the boundaries of the layer as shown

at the right-hand side of t he upper mor tar layer in Fig. 3.8. In other

cases, the separation of the l ayer from the slab propagated on ly to a point

at which the negative moment , i nduced by the res i dual load of t he ram, ,

created bending stresses in the interior surface of the mor tar l ayer which

exceeded the mortar strength. At this point a vertical crack was formed

at the interior surface of the mortar layer.

In the tests where no steel restraining plates were used, the

necessary rigidity against rotation required at the boundaries was pro-

vided by the adhesion fo rce F0 developed in the remaining area of contact

between the mortar and the surface slab. The left-hand side of the upper

mo r tar layer and both sides of the lower layer shown in Fig. 3.8 are examples

of this situation. Except in the tests in which the contact between the

steel plates and t he mo r tar layer was very irregular, the plates provided

a limit to the length of separation between the mortar layer and the fixed

wall (Figs. 3.9 and 3.10) .

In tests carried out with reinforced layers (test Nos . 15 and 16),

or for those in which the steel plates were closely spaced (tes t Nos. 17 and

3-1 8

FIGURE 3.8 MORTAR LAYERS FAILED BY SEPARATION OF MORTAR LAYER FROM THE SURFACE SLAB

FIGURE 3.9 STEEL PLATES PROVIDING RESTRAINT TO ADHESION FAILURE PROPAGATION

3-19

FIGURE 3. l O TOP VIEW OF MORTAR CRACKING PATTERN IN TEST NO. 17

18), a significant residual resistant was present in the layer even after

large displacements. This resistance was produced by an adhesion between

the mortar layer and the concrete slab covering the movable block. Once

this adhesion failure developed, another vertical crack occurred at the

surface and along the center line of the mortar layer and the resistance

of the layer suddenly approached zero. Figure 3.11 shows the three verti

cal cracks in the mortar layer, produced by bending stresses developed

during the loading in test No . 16. The cracks at the contact of the movable

block with the fixed walls, labeled Number 5, appeared immediately after

3-20

FIGURE 3.11 VERTICAL CRACKS IN THE MORTAR LAYER DUE TO BENDING STRESSES DEVELOPED BY LOADING PROCESS IN TEST NO. 16

separation of the mortar layer from the wall; the other crack, along the

center line of the movable block and labeled Number 8, appeared later,

after a considerable displacement of the movable block had taken place.

Figure 3.10 shows a similar adhesion failure and the corresponding crack

pattern, obtained in test No. 17 in which steel plates were used. The

top view of the central zone of the mortar layer in Fig. 3.12 shows clearly

the adhesion failure which developed between the mortar layer and the con

crete slab.

In other cases, such as the case shown in Fig. 3.13 corresponding

3-21

FIGURE 3.l2 TOP VIEW OF ADHESION FAILURE DEVELOPED BETWEEN THE MORTAR LAYER AND THE CONCRETE SLAB COVERING THE MOVABLE BLOCK IN TEST NO. 15

FIGURE 3.13 MORTAR SURFACE CRACKS DEVELOPED ALONG PRE-LOADING WEAKNESS ZONES

3-22

to test No. 2, the cracks in the mortar layer sur.face were not observed at

locations where stresses in the layer were maximum. In these cases, fail

ure occurred along existing cracks produced by shrinkage or relative dis

placement which occurred within the mortar layer shortly after its placement.

The load carrying capacity of the mortar layer after adhesion

failure occurred, decreased rapidly to zero for all the cases in which

steel plates were not used. This was observed independent of the length

of separation between the mortar layer and the fixed walls.

3.5.2 LOAD VS. MOVABLE BLOCK DISPLACEMENT

The mortar layer resistance and the displacement of the movable

block were monitored during the test using an x-y plotter connected to the

ram control system. The unit load, i.e . , the load divided by the 48 in.

(122 cm) of contact between the mortar layer and the fixed walls, was cal

culated and used as a measure of the resistance of the layer. The portion

of the monitored displacements due to deflection of the frame 11 fixed 11 wall

were determined by comparing at equal load levels the magnitude of the plot

ted displacements with those measured by dial gages mounted on the back of

the movable block. The magnitude of these loading system displacements was

subtracted from those measured by the x-y recorder to obtain the net dis

placements of the movable block relative to the fixed wall.

For each of the tests performed, the unit load was plotted on

they axis while its correspondent displacement of the movable block rela

tive to the fixed wall was plotted on the x axis. Figure 3.14 shows three

types of curves, corresponding to three types of structural behavior ob

served in the preliminary tests . 3-23

w I

N -,1:a

+J u "' +J C: 0 u

'+-0

.s::. +J 0) C: QJ .... +J ..... C: :::,

s.. QJ 0.

QJ u C:

"' +J VI .... VI QJ

0:::

Movable block displacements FIGURE 3.14 TYPICAL UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENT

RELATIONSHIPS FOUND IN MORTAR LAYERS

For type No. l and No. 2 curves in Fig. 3. 14 the maximum re

sistance of the layer was obtained as the layer separated from the surface

slab. The initial portion pf the load-displacement curve shows a linear

elastic behavior in which the maximum load is reached at a relatively small

displacement. The type No. l curve shows that once separation occurred the

resistance of the mortar layer dropped sharply to zero. This curve is repre

sentative of the structural behavior of the mortar layer in test Nos. 2

through 10, for which no steel plates or other types of boundary restric

tions were used.

The type 2 solid line shows an instantaneous decline in the applied

load immediately after the ultimate capacity of the layer was reached. The

almost complete reduction of load, required to switch from load to displace

ment control, did not represent an actual reduction of the resistance of the

mortar layer. Once the switch in the control was made, the load in the ram

increased with further displacements of the movable block up to a level rep

resenting the actual residual resistance of the mortar layer at that dis

placement. For further displacements of the movable block the resistance of

the mortar layer decreased at a rate determined by the stiffness of the layer

and the extension of the adhesion failure beyond the movable block. The type

2 dotted line represents the relationship that would have been obtained if

the load in the ram had not been reduced in order to switch from load to

stroke control. The structural behavior of the mortar layer for test Nos.

11 to 17 for which steel plates were used to fix the boundaries of the layer,

are represented by this curve.

The type 3 curve shows the case of test No. 8 in which the maxi

mum resistance of the mortar layer was not reached at the beginning of the

3-25

separation of the layer from the surface slab, but rather in bending with

f urther displacements of the movable block. Curve 3 follows the same path

as curves 1 and 2 up to a point that corresponds to the separation of the

layer from the surface slab; from that point the curve represents the load

deflection curve of a simply supported beam.

The structural behavior of the layers in test Nos. land 2 corre

spond basically with the type l curve. The greater value of maximum load

was the result of the presence of mortar in the gap between the surface

slab covering the movable block and those covering the surrounding fixed

walls.

The relation-ship between the unit-length resistance and movable

block displacements for each of the tests are shown in Figs. 3.15 to 3.23.

The values of the maximum resistance of the layer and the displacement at

which it was obtained together with pertinent remarks for each of the tests

are summarized in Table 3.4. From this table and the aforementioned rela

tionship plotted in Figs. 3.15 to 3.23 the following conclusions can be

drawn:

1. For the layers with load-displacement behavior represented

by type curves l and 2, the magnitude of the displacement

of the movable block at which maximum load was reached has

a maximum value of 0.004 in . (0.102 mm).

2. Residual load capacities equal to 60 to 70 percent of the

maximum capacity were observed in mortar layers whose struc

tural behavior corresponds to that shown by type 2 curves.

This residual capacity was maintained during movable block

3-26

TABLE 3.4

MORTAR TEST RESULTS

Displacement of Maximum carrying the movable block

Test capacity at max load no. lbs ( KP a) in. (cm) Remarks

l 4000 (27,800) .015 (. 0381 )

2 4000 (27,800) .016 (. 0406)

3 1500 ( l O ,340) .005 (.0127)

4 900 ( 6,200) .003 (. 0076)

5 860 ( 5,930) .001 (.0025) Layer was altered during testing set-up.

6 Failed during set-up.

7 5800 (40,000) .005 (.0127)

8 2400 (16,550) .003 ( .0076)

9 450 ( 3, l 00) .001 ( .0025)

10 1000 ( 6,895) .002 (.0051)

11 3240 (22,400) .003 (. 0076) Steel plates

12 1640 (11,600) .004 (.0102) Steel plates

13 1250 ( 8,620) .004 (.0102) Steel plates

14 1170 ( 8,070) .004 (. 0102) Steel plates

15 2500 (17,200) .002 (.0051) Steel plates

16 2300 (15,850) .003 (.0076) Steel plates

17 2850 (19,650) .002 (.0051) Steel plates

18 2600 (17,900) .075 (.1905) Steel pl ates

3-27

Movable block displacement (µm) =

20 0 100 200 300 400 500 600 700 800

100

-----E 16 . C:

......... •,-z:

~w~ ~ ~ -+.> u

l~ca le.~ "' +.> C: 1 ,. 1/0"' 20 in. 0 +-' u 12 C:

0 It- u 0

.s::::. ! 60r /~ ~ "-M-1 L = 24 in . +.> O'l (L - 610 mm) w C:

I . Q.I O'l N ,-. C: 00 ClJ

+.> ,-.

I f'f "-- M-2 L = 48 in. •r- 8 C: +.> (L = 1220 mm) ::, •,-

s.. c:: 40 ::, Q.I a. s..

Q.I Q.I a. u C: Q.I

"' u +.> C: VI 4 "' ,,- +.> 20 VI VI Q.I •r-

0::: VI (IJ

0:::

0 0 ____ ........, ___ ____. ____ ....__ ___ ___._ ___ ......... .._ ___ __._ ____ ..__ ___ _,

0 - --8 12 16 20 4 24 28 32 Movable block displacement (lo-3 in.)

FIGURE 3.15 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS

Movable block displacements (µm)

201 0 l 00 200 300 400 500 600 700 800

100 .......... . i::

~16 •r--:z:: 4-.:::L

¥801 ~ l~rta~fscale~

-----.µ u ro .µ S::" 0 lavPr 1o in . u 0

4- 12 u 0 4-

0 .. c. ..c: 60 +'

0, +' w C 0, I QJ i::

N ,-- QJ I.O .µ

.,_,

] I M-3 L = 48 in. i:: 8 ::, r (L = 1220 mm) s... QJ s... 40 0. QJ

0.

I ~/ rM-4 L = 7 in. QJ u QJ (L = 178 nm) i:: u ro i:: .µ ro (/) +'

•r- 4 (/) (/) ·;;; 20 QJ

c::: QJ c:::

0 4 8 12 16 " 20 24 28 32

Movable block displacements (10- 3 in.)

FIGURE 3. 16 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS

20r- 0 r I

100

- 16 ...-.. E E '- f 80~

z ~ ---.µ u

"' .µ c:: 0

12 c::

u 0 u

4-0 4-

..c:: 0 6 w .µ ..c I 0) .µ

w s:: 0) 0 a., c::

,-- a., ,--

.µ •,- 8 .µ s:: ,,-:::, § 40 s.. a., s.. c.. a.,

a.,

to~ u c:: "' .µ

4 VI •,-VI a., VI & a: a.,

0:::

0

Movable block displacements {µm)

100 200 300 400 500 600 700

~;;~;;~~~-:~~

/ M-5 L = 48 in. (L = 1220nm)

rM-6 L = 48 in. {L = 1220 nm)

4 8 12 16 · 20 Movable block displacements (l0- 3 in.)

24


28

800

32


20 0 100 200 300 400 500 600 700 800

100 ...--.. . - C

~ 16 .,... .......

z 4--~ ~ - ,.... .µ - 80 u .µ

"' u

I f I L Mortal' layer ~Scal~f .µ n:, - C .µ 0 C 20 in. u 0

12 u 4--0 ! 60~ I I M-7 L = 14 in.

.s:::. ~ (L = 355 mm) .µ w O'l .µ I C O'l

w (l) C ...... ,.... (l) ,.... .µ

I U\ I ~ M-8 L = 18 in . .,... .µ C 8 .,...

(L = 457 mm) ::, C ::,

s... (l) - s... 0. (l)

0. (l) u (l) C u n:, C .µ n:, V) .µ

.,... 4 V) V) .,... (l) V)

ex: (l) ex:

0 o _____ _,o\-______ ...._ ___ ___._ ____ ...._ ___ ____., ____ ..._ ____ i..,_ ___ __,

0 4 8 12 16 20 24 28 32

Movable block displacements (l0- 3 in.)

FIGURE 3. 18 UNIT LENGTH RESISTANCE VS t,OVABLE BLOCK DISPLACEMENTS

Movable block displacements (µm) 20 0 100 200 300 400 500 700 800

,oo~==~=--~--~--r---r--~=--r--1 16 -. - C

~t~ E ! 80~ -z: ~ - cale +-' Mortar laye~ ~ u "' +-' "' C 12 +-' 0 C u 0

u ~ ~ 60 0

w 0 I ..c

w +-' ..c N C') +->

C C')

OJ C ,- OJ

8 ,-

+-' .,... +-> C .§ 401 M-10 L = 48 in. ::::,

s.. / ( L = 1220 mm) OJ s.. c.. OJ - c.. OJ

~ 20 I j\ / u r M-9 L = 48 in. C

"' 4 (L = 1220 mm) +-> Vl +-> .,... Vl Vl .,... OJ Vl

cc: OJ cc:

0 0 0 4 8 12 16 20 24 28 32

Movable block displacements (l0- 3 in.) FIGURE 3. 19 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS

- Movable block displacements {µm)

20 0 100 200 300 400 500 600 700 800

100------------,----~------r----,------:r-----,------,

_161--: E C

......... . .... z ......... ..::,t. '+- 80

.0 ,-

.µ --- I L Mortar u tO .µ - .µ u

§12 tO .µ

u c:: 0

'+- u 0 '+- 60 w

I ..c:: 0 w .µ

w O'l ..c:: C .µ

I 1 I M-11 L = 46 i n . w / l / 4 11 St. pl . (l) O'l ,- c:: I (L = 1168 mm) .µ 8 (l)

,-•,-c:: :!: 40 ::::I

c::

I '~ ~ / M- 12 L = 46 in. w / l / 4 11 st. pl . ~ ::::I (l)

(L = 1168 nm) 0.. ~ (l)

(l) 0.. u c:: (l) - i 4 u

VI ~ 20 ..... .µ VI VI (l) .....

e:::: VI (l)

e::::

OL.. 0 0 4 8 12 16 20 24 28 32

Movable block displacements (l0- 3 in.)


-

-20

........ 16 E

" z ..:,,:. __,,

-- .µ u rtl .µ C 0 u 12 4-0

..c

.µ w O'l I C

w Q) .i::,. ,--

.µ •,- 8 C :::,

s.. Q)

0. - Q) u C rtl .µ V1 4 •,-V1 Q) ~

0

-

0 1.25

Movable block displacements (mm)

2.50 3.75 5.00

100--------------~----,..-----r------:r----.-----,

---. C

•,-

" 4-

~ 80 .........

I LMortar layer ~ .µ u rtl .µ 0 l • C 0 u

6 60 ..c .µ O'l C Q)

,--

.µ •,-

C 40 :::,

I rM-13 L = 48 in. W/1/4" St. pl. s.. Q) 0. (L = 1220 mn) Q)

~ (A ~M-14 L = 48 in. w/1/4" St. pl. ...., 20 ...... _ (L = 1220 mn) V1 •,-V1 Q) ~

a.__ ___ ......_ ____ ~-----'-----........_..__ _______ _,__ _________ _ 0 25 50 75 100 125 150 175 200



Movable block displacements (mm) 20 0 1.25 2.50 3.75 5.00

100------------------------------------------

-. 16 ........ s:::

E ..... '-

tw~ ~l~ z: .:¥ -+' u

_ Mortar layer ~~a~~~ ltl +' C: 0

12 s:::

<...) 0 u ..... 0 ..... ...,..,... 0 60 ..c: +' ..c: w 0, +'

I s::: O> w Q) s::: (J"1 ,-- Q) I\,,,_ M-15 L = 48 in. w/1/4 11 St. pl. .....

+' r- (L = 1220 mm) ..... 8 +' - C: ..... ~

s.. -,,v\ \ J / M-16 L = 48 in. w/1/4 11 St. pl. Q) s.. c.. Q) (L = 1220 mm) c.. Q) u C1J s::: u

. ltl C: +'

4 ltl

VI t: 20 ..... VI ..... C1J VI

0:: C1J 0::

0 0 25 50 75 100 00

Movable block displacements


--

-Movable block displacements (mm)

20 0 1.25 2.50 3.75 5.00

100

-E 16 . C:

----.,...

z ----~ '+-......., ..0

.µ .:::, 80 u ,0 .µ I L Mortar 1 ayer .µ u C: ,0 0 .µ

u 12 C: 0

'+- u 0 - ~ ; 60t M-17 L = 48 in. w/1/4" St. pl. .µ Cl ~ (L = 1220 mm) C:

w Q) Cl I

,.... C: w Q)

II \ /- l I / M-18 L = 48 in . O"I .µ ,.... (L - 1220 mm) .,...

8 C: .µ ::,

-~ 40 -- s.. ::, Q) c.. s..

QJ Q) c.. u C: Q) ,0 u .µ C: V) 4 ,0 .,... .µ V) V) Q) .,...

0::: V) Q)

0::

0a 2s 56 ?b 1b'b 1~s 1~0 1~5 2bo

- Movable block displacements (10- 3 in.)


displacements 15 to 25 times greater than the average re

quired to cause initial failure. Residual capacity of the

layers was reduced to zero at movable block displacements

equal to 1 in. (2.54 mm).

3. The presence of mortar in the gap between the surface slab

covering the movable block and the adjacent slabs increased

the magnitude of the displacements at which maximum-resistance

was achieved by a factor of 4 (0.015 in.).

4. In cases where the ram induced negative moments exceeding the

bending strength of mortar a crack showed up in the interior

surface of the layer; cracks appeared at different distances

from the movable block depending on the thickness of the layer

and the adhesion strength along the mortar-surface slab con

tact. Rock bolts located at distances further away from the

crack would not have had any influence on the resistance of

the layer.

3.5.3 MORTAR LAYER DISPLACEMENTS

GENERAL

As mentioned in Section 2.4, a set of dial gages placed against

the front surface of the mortar layer and attached to the floor was used

to measure the relative forward displacements of the layer with respect

to the floor. The pre-failure displacements measured by these dial gages

for each of the mortar layers tested, are shown in Figs. 3.24 to 3.39.

3-37

M-1

0

50

....... E

w ;::l l 00 ---I w .µ co C

QJ

O 150 E QJ u rd

,--0. Vl 50 .,....

-0

,--rd

~ 100 0 S,...

LL

150

i

6 4 3 2 h Scale ., I 20 in.

Load O

550 lbf (2.2 kN)

1000 lbf (4.4 kN) ~~~:..;-;"";;=;=;;;~i:•;:~~: 1500 lbf (6.7 kN) ~--=:;:.;_-__:_:_:__:-_-_-_-_-_-_:_;.::::::s--: 2000 lbf (8.9 kN) _ 2250 lbf (10.0 kN) -

2500 lbf (11. l kN) 2750 lbf (12.2 kN) 3000 lbf (13.3 kN) 3250 lbf (14.5 kN) 3500 lbf (15.6 kN) 3750 lbf (16:7 kN) 4000 lbf (17.8 kN)

FIGURE 3.24 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR

20

40

60 --.o

200

400

600

......... . C .,....

,;:t-I 0 ,..... ..__.,

.µ C QJ E QJ u rd ,..... 0. Vl .,....

-0

,..... rd .µ C 0 s.. u..

M-2 i

_!_. -. --:;.--. ~ -~

cb © ©0 0 0 0 0 0 ~ Scale 20 in. • I

Load 0 Or-500 l bf ( 2 . 2 kN)

1000 lbf (4.4 kN

50 ~ 20 -

C ----E .,....

40 ;:1.

100 I.O .......... I w 0 I I-,-w z .......... I.O LLJ

60 ::::E 150 0 .µ LLJ 0 1500 lbf (6.7 kN) C u (1.) ct:

12000 lbf (8.9 kN) E _J

(1.) CL I I

:!2250 lbf (10.0 kN) 200 u V') I

l'tl ...... 500 • I ,-I . =-----=-----• • 2 500 lb f ( l l. l kN) Cl 0. (./) _J • ~2750 lbf (12.2 kN) .,.... cl:

3000 lbf (13 . 3 kN) 400 -0 ~ 1000 3250 lbf (14.5 ~N) ,-

l'tl a::: 3500 lbf (15.6 kN) .µ LL.

C

3750 lbf (16.7 kN) 600 0 s.. 1500 L I-- 4000 lbf (17.8 kN) LL.

FIGURE 3. 25 FRONT FACE DISPLACEMENT OF LAYER W .T .R . FLOOR

M-3

0

50

.......... w E 100 I

;:!.

~ -0 .µ C: 150 Q) 0 E Q) u ~ ,-0. 500 VI .,.... -0

,-~ 1000 .µ C: 0 s...

LL

1500

i

6 5 6 7 ~ Sca~e • I 20 1n.

.. -

Load 0

__ 250 1 bf ( 1 . 1 kN) - / 500 lbf (2.2 kN __/' ~ 750 lbf (3.3 kN..J--120

l 000 l bf ( 4. 4 kN

40

60 --------------1250 lbf (5.6 kN)


C: .,.... ,;;:J-

I 0 ,-...... .µ C Q)

0 E Q) u ~

200 ~ .,.... -0

400 _e

600

C: 0 s...

LL

M-4

0

50 ,......... E

w ;::1 l 00 I -~ +-> t:: QJ 150 E 0 QJ u r1:l ...... c.. Vl 500 ..... -c ......

r1:l +-> 1000 t:: 0 S-

Lt-

1500

<t.

6 4 3 2 ~ Seale • I 20 in.

Load 0

- 920 lbf (4.1 kN)

500 lbf (2.2 kN) 20

40 To 2030 To 2030

60


,......... . t:: .....

tj" I 0 .... -+-> t:: QJ

n E QJ u r1:l ...... c..

200 Vl ..... -c r-r1:l

400 +-> t:: 0 S-

Lt-

600

M-5 <t.

I •-.7 .- ~-•-• '.,-

6 .12 r Scale • I 20 in.

0 Load

500 lbf (2.2 kN) ..........

5 20 . s:: .,....

--.. E

100 w ;:l.. I ----.i:,.

40

o:::t I 0 ,-

----N +-> s::

150 Q.)

0 E Q.)

u c-s

60

.µ s:: Q.)

E Q.) u c-s ,-

c.. 500 VJ .,....

-0

,-

200 c.. Vl .,....

-0 ,-c-s

+-> 1000 s:: 0 s... u..

,-

400 c-s .µ s:: 0 s... u..

1500 600


M-6 t..

~-~-~

6 @ d) 0) ® ® © © 6 r4 Seale 20 in. ~ l

0 Load 0

,,.....,

20 . 50 s:: .,....

---- ,q-E I ;::l

100 40 0 w ---- ,-I ----~ .µ 'J.) s:: .µ

QJ s:: E 150 60 QJ QJ 0 0 E u 200 lbf (1.2 kN) QJ <tl u ,- ro 0. ,-Vl

200 0. .,.... 500 Vl -0 .,....

-0 -ro ,-.µ

480 ro § 1000 .µ

s:: s.. 0 LJ... s.. LJ...

1500 600


M-7 t

4) l...5) l...6) l7 J lB J l9 J I~ Seale 20 in.

• I 0 ,- ,Load

0 1500 1 bf ( 6. 7 kN

3500 lbf (15.6 ~ -50 ~ I- 5500 lbf (26.5 kN

20 s:::: .... -100 t t tj-

E I ;::1.

40 0

w .__.. r-

I +J ~

I 0 150 t t j60 a I ~

15of ~ ~200 ! r-

lt:l

j 1000~ r 7400 i LL

15001 I __, 600


M-9 i

~-•"• ~-~···· ·

6 © 0 ~ © © cb © © I Seale 4

20 in. . l 0 ,--

200 1bf 0

( 0. 9 kN) -20

. 501- t- ........... "'ti"" / • ----- 300 lbf C: . ....

( 1. 3 kN) -=:t"

E

t I 0

;:1. lOOt 40 ,-w .......... .......... I ~ .µ .µ (J1 C: C:

Q.)

150 60 Q.)

E 0 0 E Q.) QJ u u .,, .,, ,- ,-C. 200 C. V)

500 V) ..... . .... -0 -0 ,- ,-.,, .,, .µ

1000 400 .µ C: C: 0 0 s... s...

LL LL

1500 ' . _600

FIGURE 3.31 FRONT FACE DISPLACEMENT OF LAYER W.R. T. FLOOR

M-11

0

50 --.. E ;:l.

----w .µ 100 I s:: ~ Q)

°' E Q)

150 u 0 10 ,...... 0.. (/)

·r--0 500 ,...... 10

+-> s:: 0 1000· S-

LL

1500

'i.

0 3 4 5 I-. Sca~e • I 20 1n.

Load 0 500 lbf (2.20 kN)

1000 lbf (4.40 kN) 1500 lbf (6.70 kN) 20

2000 lbf (8.90 kN)

2500 lbf (11.10 kN 40 3000 lbf (13.30 kN

60


---. c:: .....

-=::t" I 0 ,...... ----.µ c:: QJ E

0 QJ u ta

,--0.. (/)

200 ..... -0 ,--ta ~

400 c:: 0 s...

LL.

600

M-12 't.

1/4 11 Steel plate Steel plate .....

.12 11 1~ Scale I 20 in. •

0 Load

500 1 bf ( 2. 2 kN) i ·0 1000 lbf (4.4 kN) -

20 .

C: .,.. -E ;::1.

w ---._,.

I

40 0 ,--

I ~

.µ

....... C: (1.) E (1.) 150 u 0 ~

,--a. Vl ,,-

"'C 500 ,--~ .µ C: 1000 0 s..

LL

---1500 lbf (6.7 kN)

]60 ··O i ho ···-r1 r 2000 lbf (8.9 kN)

i jzoo J 870 3576 4150 3673 ,--

400 ~ .µ C: 0 s..

LL

1500 600

FIGURE 3.33 FRONT FACE DISPLACEMENT OF LAYER W.R.T.FLOOR

M- 13 ( l )

0

50

......... w E 100 I ;::I. ~ -co .µ

C: O 150 a, E a, u <l:l ,-a. 500 Vl .....

"'C

.µ C: 1000 0 s..

LL

1500

t

1/4" Steel plate

0 3 4 5

1/4" Steel plate

h Scale .I 20 in.

Load 0

I \ I ~ :::::::-,,• 7 350 lbf (l.60 kN) I

480 lbf (2.~0 kN) 1000 lbf (4.40 kN) 1250 lbf (5.60 kN)


20

40

60

. C: .....

._,.. I 0 ,--

0 t a, E a, u

200 ~ a. Vl

"'C

400 +'

600

C: 0 s..

LL

M-14 (l)

0

50

..--.. E 100 w ;::l

I .......... ~ \.D +-'

C QJ

0 E QJ u 10

,--Cl.. l/l 500 ..... -0

,--10

~ 1000 0 ~

LJ..

1500

0 l/4 11 Steel

plate

2

i

Jl JO

plate

I~ Sca~e 20 ,n.

Load 0

20

40

7 5 0 l b f ( 3 . 3 kN ) 60

1000 lbf (4.4 kN) ll 7 5 l b f ( 5 . 2 kN )


• I

....... . C .....

o:::i-I 0 ,--..........

0 ~

loo j Cl.. l/l ..... -0

400 .--10 .µ C 0 ~

600 LJ..

E ;::l

w -I u, .µ 0 C:

Q) E Q) u ttl ...... 0. Vl ...... " ...... ttl .µ C: 0 s....

LJ...

M-15 (1)

0

50

100

o 150

500

1000

1500

i

1/4" Steel plate Steel plate ~-·~·· ~·-.:.:-

6 { l J l 2J { 3) l 4 h Scale I 20 . •

,n,

Load 0 I -......::::: QiQf 9V :::::--Soo 1 bf (2. 20 kN) I

1000 lbf (4.40 kN) 1500 lbf (6.70 kN) 2000 lbf (8.90 kN) 2500 lbf (11.10 kN


20

40

60 0

. C:

,;:j-1 0 ...... -.µ C: Q) E Q) u ttl ...... 0.

200 -~ " P"'!'" ru .µ

400 §

600

s.... LJ...

M- 16 ( l ) i

1/4 11 Steel plate 1/4 11 Steel plate z:s. ,;;:; .... • e cf

c5 11) (IO) (q) (8) ( ) r4 Seale ~ I 20 in.

0 0 500 lbf (2.2 kN)

50 .......... E

1000 lbf (4.4 kN) . 15 00 l bf ( 6 . 7 kN ) j 2 0 i:::

2000 lbf (8.9 kN) .,....

o:::r I

;::l.

ioo ~

w 40 0 ,...... ~

I .µ tTI i::: __, a,

E a, u 0 r!j

.µ i:::

60 _ 0 a, E a, u - ,......

a. r!j ,......

V) ..... 500 -0

200 ~ ..... -0 ,......

r!j .µ i:::

1000 0 ~

LL..

,...... r!j

400 +' i::: 0 ~

LI..

1500 600


M- 17 ( 1 )

0

50 ,,-... E ;::1.

w ......... 100

I .µ u, s:: N

~ Q) 0

150 u r0 -0. Vl .,.... 500 "'CJ

,--r0 .µ

§ 1000 ~

LL

1500

i

1/4 11 Steel plate

6 4

1/4 11 Steel plate

Load 350 lbf (1.6 kN)

1000 lbf (4.4 kN) 1500 lbf (6.7 kN) 2000 lbf (8.9 kN)

h Sea le I 20 in. "

,a

2500 1 bf ( 11. 1 kN) ~20

40

,,-...

s:: .,.... tj-

I 0 ,--......... .µ s:: Q)

60 _o E Q) u r0

,--0.

200 -~ "'CJ

,--r0

400 t 0 ~

LL

600


M-18 (l)

--0

50

......... E 100 ;::1. w -----I

u, +,) w C: (1) O 150 E (1) u - re ,-0.

500 C/l •r-"'C

,-rt:$

+,) 1000 C: 0 s..

LL.

1500

t.

1/4 11 Steel plate _ II I I ,- 1/4 11 Steel plate h-lP· h · ·· · 8 J

11) no) (9) (X) (X ) ~ Seale .. ( 20 in.

Load

430 lbf (l.90 kN)

1000 lbf (4.40 kN)

1500 lbf (6.70 kN)


0

7 20·

40

60 0

. C:

•r-

'<:t" I 0

+,)

C: (1)

E (1)

u re ,-

200 ~ •r-"'C

"400 i

600

C: 0 s..

LL.

The post-failure displacements of the layers having a structural behavior

similar to curve 2 in Fig. 3.14 are shown in Figs. 3.40 to 3.45.

The upper part of the figures show a schematic view looking

down on the mortar layer and the covered fixed wall and movable blocks.

The positions of the frontal dial gages monitoring the mortar layer dis

placements are also shown. The displacements recorded by each one of the

dial gages at every load increment dur1ng the loading process are plotted

in the figure, directly beneath the gage. A displacement profile of the

front face of the mortar layer during the loading process was obtained by

joining with a line the displacements measured in all the gages at the

same load increment. ' The magnitude of the total load on the mortar layer

at every load increment is shown at the right side of the displacement

profile.

DISPLACEMENT PROFILE CHARACTERISTICS BEFORE INITIAL FAILURE

The characteristics of the displacement profile, before initial

failure occurred, were very similar for all the tests. Initially, equal

increments of load corresponded with equal increments of displacement of

the front face of the mortar layer. There was an elastic relationship

between the forward displacements of the mortar layer and the load in the

jack.

The magnitude of the forward displacements was slightly greater

along the vertical center line of the mortar layer, and decreased slightly

away from the center line. The rate at which this value decreased with

distance depended mainly on the stiffness of the contact between the mortar

layer and the surface slabs on the fixed walls. It also depended on the

3-54

;

-

0 ,--

,w · ·, -g: . ~ ..._,,

+.)

~ 0.5 Q,J u ,0 ,.... 0. VI .,.... .,,...

"'O

'; 1.0 +,) s::: 0 ~

LL

I

1.5

M- 13 (2)

I

l/4 in. steel plate

Ci_

I

.......... ,,

FIGURE 3.40 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR

~4

Scale .,J 10 in.

1/4 in. steel plate

Load

860 lbf (3.8kN) 830 lbf (3.7kN

800 lbf ~3.6 kN~ 700 lbf 3.1 kN 650 lbf (2.9 kN) 560 lbf (2.9 kN) 510 lbf (2.3 kN 480 l bf ( 2. l kN 415 lbf (1.8 kN) 340 lbf (1.5 kN) 181 l bf ( 0. 8 kN)

I

0

200

400

,,....... . s::: .,....

M I 0 ,---+,) s::: QJ E QJ u rtS

,--0. VI .,....

"'O

,--rtS

+.)

C: 0 ~

LL

,,,._

or W ..-...

Ji i m-

~ 2.50 cu E cu u

'° ..... c.. Ill ..... -0

,- 5.00

'° .µ C: 0 s..

&..

7. 50 I-

-

M-14 (2)

l / 4 in. steel II plate

1

~ @ ..__,,

L \

~

I I

..__,,

I

..__,, ..__,,

I

1• Scale ...I l O in.

\ 1/4 in. steel plate

..__,, Load

0

.---. 550 lbf (2.4 kN)

s::: •,-

C"")

I

100 ~ .......... .µ

580 lbf (2.6 kN) C:

~ Q) u ro ,-c..

200 Ill •,-"'C

465 lbf (2.1 kN) ,-ro .µ C: 0 s..

LL

_J 300


-M-15 (2)

- -0,-

w I .........

c.n ~ -...J ._...

.µ l O C (1)

E (1) u .,, ,-0.. V) .....

"'Cl

20 .... .,, .µ C 0 ~

l.J..

30~ L

-

1/4 in. steel plate

- -

'\.

4-1 I

- - -

------- ,,,,,,. -- / /

//

/ / /

/ // // /

,, / I ,,"' / I

/ / / /

/ I / I

/ / / I

/ I / I

/ I

I I

/ /

I


I• Scale ►~ l O in.

in. steel plate

- Load

· 2500 lbf (11.7 kN)

460 lbf (2.0 kN)

1400 lbf (6.2 kN)

0 ......... .

C: ..... ('Y')

I 0 ,--200 ...., C: (1)

E (1) u .,, ,-c.. V)

•,-400 -o

,-.,, .µ C: 0 ~

l.J..

~600 970 lbf (4.3 kN)

--M-16 (2)

,_,,.

0 --

w -1 E u, E CX> ..__...

.µ

~ 0.5 E Q) u rt! ,-0. V) .,.... -0

.-- l 0 rt! • ,.. .µ c:: 0 S-

LL.

1.sL L

-

l / 4 in . steel plate

"-

~

I I

• /

~•Scale .,J l O in.

in. steel pl ate

-Load

LJ'tV IUI \ I V • 't 11.1,

1400 lbf (6.2 kN)

0 -. C: -~

CV)

I 0 ,-

20 ..__... .µ s::: (1)

~ u ttJ ,-0. VI

40 .,.... -0

,-

"' .µ c:: 0 S-

LL.

~ 700 l bf ( 3. l kN) J6o


--M-17 ( 2)

.,... or ----w -E I

c.n -I.O .,._,

1- C 5 QJ

&l u ,0 ,-a.

·VI .,.. -0 ,.... 10 rel ,µ C 0 s..

LL.

15~ L

--

1/4 in. steel plate

r: 't..

..

f---Sc~_ ···--i 10 in.

in. steel plate

Load

2880 lbf (12.8 kN)

1680 lbf (7.5 kN)

1770 lbf (7.9 kN)

0

200

400

.......1600


----. C ,,-

CV)

I 0

,µ C (l)

E (l) u rel ,-0.. VI .,....

"O

,--rel ,µ C 0 s..

LL.

-

-

w

!sl --- I 0)

0

QJ

~ u ,0

----,-0. V) .,...

"C

,_ 10 ,0

-+-> C: 0 s.. I LL

15l-

--1

M-18 (2) Ct

I ~S~ a 1 e _ ··-i 10 in .

1 / 4 in • s tee 1 plate

1/4 in. steel plate

Load 0

1700 lbf (7.6 kN) I ----.

L ~ 2170 lbf (9.7 kN) J 200 i

\ -----1 -+-> 2000 lbf (8.9 kN) s::::

QJ --------- E QJ

1900 lbf (8 . 5 kN) u tO - - ,--- 400 ~ ---- .,... -- "C

I I tO -+-> C: 0 s..

LL

L _J 600


relative stiffness of the layer with respect to the movable block and on

its length. For example, in test Nos . 4 and 7 which had relatively stiffer

layers extending for smaller 'distances -, 7 in. (17.8 cm) and 14 in. (35.6

cm) respectively, away from the movable block, the forward displacements

along the layer were more uniform than in the other tests.

In some cases where mortar was present in the slot surrounding

the movable block (test Nos. 1 and 2), the magnitude of the forward dis

placements of the mortar layer at failure was 3 to 4 times greater than

the average value obtained in the other tests and the shape of the dis

placement profile was less pronounced.

DISPLACEMENT PROFILE CHARACTERISTICS AFTER FAILURE

The post-failure displacements of the mortar layers in which the

structural behavior is represented by curve l in Fig. 3.14 occurred very

rapidly and couldn 1 t be measured. For mortar layers having load-deflections

similar to curves 2 and 3 these displacements show a shape very similar to

the deflection curve obtained for a simply supported beam with a centered

uniformly distributed load. The forward displacements of the layer have

a maximum value along the section covering the movable block and gradually

reduce to zero at the points where the steel plates were located, except

in test Nos. 11 and 12 where the adhesion failure propagated beyond the

plates.

The rate of decrease in these displacements away from the movable

block depends mainly on the stiffness of the layer and the distance between

the steel plates. As expected, the post-failure displacements for the mor

tar layers which are represented by curve 3 in Fig. 3.14, test No. 17, are

3-61

• !

similar to those obtained in the other tests. For all tests, the general

pattern and the values of the forward displacements of the mortar layers

before and after failure, corresponds very closely to the structural be

haviors described in the preceding section.

3.5.4 STRAINS INDUCED IN THE MORTAR LAYER DURING THE LOADING PROCESS

Whittemore Points were placed on the outside surface of the mor

tar layer to monitor longitudinal _strains during the loading process.

Figures 3.46 to 3.53 show a top view of the fixed walls, the movable block,

the mortar layer and the position of the Whittemore Points. The direction

of the strains along the mortar layer surface during the loading process,

determined by the relative displacement of the Whittemore Points with re

spect to each other, is shown in the lower part of the figure. In most of

the tests a zone of tensile strain was created in the outside surface of

the mortary layer covering the movable block and its surroundings. Compres

sion strains were observed in zones away from the movable block.

This state of strain in the outside surface of the mortar layer

corresponds exactly with the state of strain that should develop to fit the

structural behavior (profile displacements) described in previous sections.

In some cases compressive strains were measured along the full length of the

mortar layer (test Nos. 11 and 17) while on others both compressive and ten

sile strains occurred on the mortar covering the movable block (test Nos. 9

and 13). These differences in strain distribution resulted from large dis

tances between adjacent Whittemore Points. The Whittemore Points were lo

cated in such a way that part of the mortar layer surface between them was

3-62

w I

O"I w

M-1 ct 11? i n

11_.~

l I L I C:. Max strain +0.002 in. I I

{between 5-6l = = ~, -1 2 3 4 5 6 7

I· Comp. + Tens. +Comp4

M-2 <t.

I Max strain +0.0066 in. ( 3-4) ....... WWW - - - t.J ] - - - WWW I

lA 18 1 2

Comp.

3 4 5 6 7 8

.. I JensJ JensJ JensJ fonip_.l. Points Lost

9

Tens. = Tensile Comp. = Compression

FIGURE 3.46 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER

w I

°' ~ I

M-3

Max strain +0.0004 in. (between 5-6) - r\

-3 4

Tens. Comp. Tens. Comp. ~

M-4

Max. strain -0.0003 i::i(between 5-6) ~

-

i

I

Tens.

't

I

No l'lO

strair .

6 5 l 4 2 3

Comp . l Comp . . . ~ .

-9 0

No l'W

Comp. s trai r


I ] o i !1J·

I Tens. = Tensile Comp.= Compression

M-5 i

[ I I ] Max. strain +0.0001 in] - • - ~-:!: W W WWW

,,.o i ~1

2 3 4 5 6 7 8 9

I· No strain ·I· Tens. • 1~t~~i~ M-6 i

w

i I

I O'\

L I Max. strain l (.J1

& m N C, +0.0008 in.~

• ...a m a l 2 3 4 5 6 7 8 9

~ No strain • 1·

Tens. + Comp. ~ Tens. = Tensile

Comp. = Compression


w I

m m

I

[

M-7 i

1 J:Max. strain +0.0005 in.

I

I I - a:..: yr - :a 2 3 4, 5

~ Tens. ~ M-9 't

Max._ strain •:.oO~~i .1 J ··- - ,-,, • ,., J l 2 3 4 5 6 7

~ No

Tens. Comp. strair Comp.

Tens. = Tensile Comp= Compression


w I

0)

--..J

M-11 i

-L _,l ... J. I I Max. strain z:S2 • • -0; 00~5 2 n .

4 ...... •• µg;

,,.a i ri•i

2 3 4 5 6 7

~ Comp. +ComP,·!$om~Jom~.Com~ up to up t crack crack

M-12 no strain<t_ tens. afterward! afterwards

I I-Max. strain +o •. o:s in:\t --~ J av • >

14 13 12 11 10 9 8

~t~~i nl ri Tens. ~ Tens. = Tensile Comp. = Compression


w I

O')

00

M-13

I C ... • u -No

~ train

2

i

L ;l ,. J ~:;:· ~train -0.0006 in] 10 in J I• p

3 4 5 6 7

Tens. Comp. Comp. up to crack tens. afterwards

M-14 <t

i Max. strain +0.0022

14

in;) 13 .- ~

l "' - as •=

11 10 9 8

Tens._l No strainlTens.lTens. up to crack comp. afterwards Tens.= Tensile

Comp.= Compression


w I 0)

\.0

M-15 i

I

[

- I .

M-16

•

t ] ,ax. strain +0.0006 in. I ... I ... .. ~ -l 2 3 4 5 6 7

~Comp+ Tens. +Campi

i

-<G __ L .1.J:::x._s_t:: ::022 in. I

l 2

Tens. I Comp. up tolup to crack crack

3 4

Tens.

comp. tens. afterwards afterwards

5 6

Comp.

7

Tens.= Tensile Comp.= Compression


w I

--..J 0

M-17 i I 1,0 ; ~~

~1 [_ _ l J::train -0~004 in~J _r~ - --~ __. ""'wF WWW

I

2 3

L Comp. J M-18 Ct

Max. str:i: _0.0009 in . . E t l :.ws -2 3

Tens.~Comp. r • •

,,, .I

Tens. = Tensile

Comp.= Compression

FIGURE 3.53 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTNESOMETER

subjected to compressive strains while the rest was under tensile strains,

so that the relative displacement measured between the two points was the

resultant of the two opposite strains. Reducing the distance between adja

cent Whittemore Points would lead to a more realistic measurement of the

distribution of strains in the surface of the layer.

3.6 SIGNIFICANCE OF VARIABLES

Each one of the 18 performed tests was planned in order to show

the importance of a particular variable in controlling the structural be

havior of the layer. During a pair of tests all variables, except one,

were kept as constant as possible. Table 3.5 indicates which tests were

used to compare the effects of each chosen variable. The table contains

eighteen rows and columns corresponding to a specific test. The variable

studied is shown in the table at the location given by the tests carried

out for its comparison. For example, test Nos. 1 and ·2 were carried out

to determine the influence of the length of the mortar layer relative to

the edge of the movable block on its structural behavior.

The importance of each variable will be discussed based on its

effect in controlling the maximum and residual resistances of the mortar

layer. The structural test results are discussed as follows.


A great number of tests (Nos. 1, 2, 4, 7, 11, 12, 17 and 18) were

performed to establish the importance of this variable. The analysis and

discussion of the results were divided into groups according to the

3-71

TABLE 3.5

VARIABLES COMPARED BETWEEN TESTS

Test no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1 2 L 3

4 5 L 6 L 7 M L

w 8 Lo I

--..J 9 M M M M N

10 Lo 11 S-8 12 S-8 13 s s 14 s s 15 Re Re 16 Re Re 17 S-4 S-4 18 S-4 S-4

LEGEND: s = Surface conditions Lo = Load rate Re = Reinforcement S-8 = Steel plates 8' apart L = Length of the mortar layer S-4 = Steel plates 4' apart

relative to the edge of the M = Mortar strength movable block.

structural behavior of the layers described in Section 3.6. The differ

ence between these structural behaviors was dependent on whether or not

steel plates were used as boundaries of the mortar layer.

Figure 3.54 shows the resistance-displacement relationship for

test Nos. l, 2, 4 and 7 in which the layer exhibited a structural behavior

corresponding to the type l curve in Fig. 3.14. The slight deviation from

this pattern shown by test Nos. l and 2 was caused by presence of mortar

in the slots between the surface slabs. The higher value of the maximum

layer resistance per unit length of contact, 105 lbs/in. (19 kn/m) was ob

tained in test No. 7 for a mortar layer extending 14 in. (35.5 cm) away

from the movable block. A similar value (61 lbs/in.) was obtained on test

Nos. l and 2 where the edge of the mortar layer was located 24 in. (61 cm)

and 48 in. (122 cm) away from the movable block, respectively. The lower

value of the maximum resistance was obtained in test No. 4 in which the

mortar layer extended only 7 in. (17.8 cm) away from the movable block .

It could be concluded from these tests that in the absence of

boundaries the length of the mortar layer beyond the movable block only

affects the maximum resistance of the layer. In addition, the length of

the mortar layer beyond a certain distance, between 7 in. (17.8 cm) and

14 in. (35.5 cm) for these cases, did not have any influence on the struc

tural behavior nor support capacity of the layer. The relatively small

magnitude of this limiting distance indicates that the distribution of ad

hesive stress between the mortar layer and the surface slab, is restricted

to relatively narrow bands on each side of the movable block. However,

the actual width of these bands does not necessarily range between 7 and

3-73


20 0 100 200 300 400 500 600 700 800

100 .........

c:: .- 16 .,_

'-E ..... '- ..ci. z ~

.--__. ------ao .µ .µ u u re, re, .µ .µ c:: c:: 0

12 0

u u ..... ..... 0 0 60

..c ..c w .µ .µ

I Ol Ol '-I c:: c:: ..i::,. Q.) Q.)

.-- .--.µ

8 .µ

•,- •,-c:: c:: ::::i ::::i40H r; I M-7 s... s... Q.) Q.) C. C.

Q.) u c:: ro .µ 4 Vl ·r-Vl I Vl Q.) Q.)

a:: a::

0 00 4 8 12 16 20 28 2

Movable block displacements (lo- 3 in.)


14 in., as suggested by the above test results , since independent tests

indicate that the lower value obtained in test 4 may have been caused by

shrinkage rather than by limiting the actual length over whic h adhesion

could be developed. Thus the actual length over which the adhesion stress

is distributed may be less than 7 in . (17.8 cm).

The resistance-displacement relationships for test Nos. 11, 12,

17 and 18 are shown in Fig. 3.55. Three of the tests, Nos. 11, 12 and 17.

have a similar structural behavior corresponding to the type 2 curve in

Fig. 3.1 4. In the other test the layer behavior is similar to that ex

hibited by the type 3 curve. The maximum resistance of the layer for test

Nos. 11, 12 and 17 varied between 30 lbs/in. (5.5 kN/m) and 60 lbs/in.

(11 kN/m) and was independent of the relative position of the steel plates

with respect to the movable block.

The locat ion of the steel plates closer to the movable block in

test No. 17 increased the level of the residual resistance of this mortar

layer to twice the value obtained in test Nos. 11 and 12. In addition,

this r esidual resistance was maintained for displacements approximately

twice those shown in test Nos. 11 and 12, giving more ductility to the

layer .

The mortar layer in test No. 18 had a res istance in bending that

was greater than the resistance in adhesion. The high resistance of the

layer when behaving as a beam is attributed to the location of the steel

plates in close proximity to the movable block.

3-75


20r-- 0 0.5 1.0 1. 5 2.0 2.5 3.0 3.5 4.0 I I I

100

.--.. . .--.. 16 C:

•,-E ......_ ......_ '+-z: ..0 .:.t. ,-..__.. ..__.. 80 .µ .µ u u ~ ~ .µ .µ C: C:

8 12 0 u

'+- '+-0 0 60

..c ..c 1/11\ M-18 .µ .µ w en en I C: C:

......i QJ QJ (J') ,- ,-

.µ 8 .µ •,- •,-C: C: :::,

: 40 nrT ~ s.. / ........ M-17 - -QJ QJ 0. 0.

QJ QJ u u C: C: ~ ~ .µ

4 .µ 1/l -~ 20 •,-1/l 1/l QJ QJ

c::: c:::

0 20 40 60 80 100 120 140 160



3.6.2 SLABS SURFACE CHARACTERISTICS

Test Nos. 13 and 14 ~ere performed with mortar layers similar to

the ones used in test Nos. 11 and 12 except that in test Nos. 13 and 14

filament tape was used to reduce the adhesive strength between the mortar

and the surface slabs along 6-in. (15.2-cm) vertical bands on either side

of and adjacent to the movable block.

The resistance-displacement relationships for tests Nos. 11, 12,

13 and 14 are shown in Fig. 3.56. All tests showed a similar structural

behavior corresponding to the type 2 curve in Fig. 3.14.

The mortar layers in test Nos. 13 and 14 had approximately the

same value, 22 lbs/in. (4 kN/m}, of maximum resistance. Higher values of

the maximum layer resistance, 30 to 60 lbs/in. (7 to 11 kN/m), were obtained

in test Nos. 11 and 12. No differences were observed in the level of the

residual resistance of the layers, but shorter displacements of the movable

block were required to reduce completely the residual resistance of layers

11 and 12.

As indicated in these tests a direct relationship exists between

the adhesive strength acting along the mortar layer-surface slab contact

and the value of the maximum resistance of the layer. The variation of

this adhesive strength does not show any influence on the residual resist

ance value. The higher rate of reduction for the residual resistance with

respect to the movable block displacements, was caused by the poor constraint

offered by the steel plates in test Nos. 11 and 12.

3-77

Movable block displacements (mm) 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 I I I I I I I I I

,......20 --. E s:: '- .,.... 5.0 z: '-~ i+- 100 .__.. ..0

,--.µ .__.. u i 16 .µ

u s:: ~ I 4.0 0 u C 8Q

0 4- u 0

4-

-512 0

en ..r::::. 3. 01-r ---- M-11 s:: 61 601 a.,

,-- s:: a.,

w .µ ,-- (./) UI ---- _M-12 I .,.... c.. -...J s:: .µ .,.... 00 ::, 8 .,.... ~

C s... ::, .. 2. QIU, / ,.-M-13 a., 40 -0 c.. s... ,,:s

a., 0 a., c.. ....J llr' / ,-- M-14 u s:: a., ,,:s u .µ 4 C (./) ,,:s .,.... .µ 20 (./) (./) a., .,....

c:::: (./) a.,

c::::

Ql_ 0 - 20 40 60 80 100 120 140 160 Movable block displacements (10- 3 in.)


3.6.3 MORTAR STRENGTH

The mortar strength of the layers used in test Nos. 3, 7 and 9

was successively reduced, see Table 3.3, by decreasing the time of curing.

As seen in Fig. 3.57, the resistance-displacement relationships

for these tests are similar to that shown by type l curve in Fig. 3.14.

The highest value of the maximum unit resistance was obtained in

test No. 7 and decreased successively for test Nos. 3 and 9. These results

indicate that the strength of the mortar in the layer directly affects its

maximum unit resistance. This is expected since the adhesive strength of

the mortar layer depends in part on the time of curing.

3.6.4 USE OF REINFORCEMENT (IN THE MORTAR LAYER)

Test Nos. 11, 12, 15 and 16 were performed in order to determine

the effect of mesh reinforcement on the structural beh~vior of the layer.

As seen in Fig. 3.58 the structural behavior of the layers in

these tests is similar to that shown by the type 2 curve in Fig. 3.14. The

maximum unit resistance is very close for test Nos. 11, 15 and 16 and has

an average value of 50 lbs/ft (9 kN/m). The lowest value of this resistance,

in test No. 12, was probably caused by pre-test cracking of the mortar layer.

The tests indicate that there is no significant difference in maximum re

sistance of mortar layers with or without reinforcement.

A considerable difference exists, however, in the residual resist

ance of the reinforced and non-reinforced mortar layers. The reinforced

layers exhibit higher residual resistance and lower rates of reduction of

this resistance with displacement of the movable block. The reinforcement

3-79


0 100 200 300 400 500 600 700 800

I I I I I I I 20 r-- ......... .

I s:: 5.0 E •r-

'- ~ 100 z .:,,,'_ ..0 ,......

..µ 16 ----u ..µ res u

801 4.0 ..µ res

s:: ..µ 0 s:: u 0

u 4-0

12 ~ H 0 c.. .s::::.

:5 6 ~3.0 ..µ O>

O> o -o I s:: I I .--M-7 aJ s:: res ,...... aJ 0 ,...... _J

..µ w •r-

8 ..µ

I s:: •r-co ~ s:: 40L 2.01-f r ,_M-3 0 ~

s.... aJ s.... c.. aJ

c.. aJ

20L 1.0 I / / I ,........... u aJ ~M-9 s:: u

t'CS 4 s:: ..µ res V) ..µ

•r- V) V) •r-aJ V)

c:::: aJ c::::

0 0 4 8 12 16 20 24, 28 32

Movable blnck displacements (l0- 3 in.)



0 0.5 l. 0 l . 5 2.0 2.5 3.0 3.5 4.0

201~

I I I I I -----E

-----z: .::,,:_ l 00 ..0

...--+-> u rt) 16 +->

+-> u s::: rt)

so1 0 +-> 4. u s::: 0

4- u 0

4-.s::: 0 +-> 12 Ol .s::: s::: +->

601 3. Q) Ol ,- s:::

QJ

+-> ,-•r-

40~ i s::: +-> w :::i •r-

8 s::: I s... :::i co Q)

---' c.. s... Q)

QJ c.. u s::: Q)

ro u +-> s::: Vl 4 rt)

20L- l. •r- +-> Vl Vl Q) •r-

0::: QJ 0:::

0 0 - 0 l'.'.U 40 bU ~u

Movable block displacements


controls the residual resistance of the layers since it increases their

stiffness and ductility. The maximum resistance offered by the reinforced

layer may develop after separation from the surface slab if the reinforce

ment increases the moment capacity of the layer to a level above its ad

hesion strength.

3.6.5 RATE OF LOADING

Two sets of tests carried out with 3-day old layers (Nos. 7 and 8)

and 7-hour old layers (Nos. 9 and 10), were used to determine the influence

of the rate of loading on the structural behavior of the layer. The struc

tural behavior of al1 the tests was very similar to that shown by the type 1

curve in Fig. 3.14.

For test Nos. 7 and 8 the maximum resistance of the mortar layers

were 110 lbs/ft (19 kN/m) and 50 lbs/ft (9 kN/m), respectively, the higher

one corresponding to test No. 7 performed with the smaller rate of loading

2 lbs/sec (8.9 x 10-3 kN/sec).

For the other set of tests, Nos. 9 and 10, the maximum resistances

of the mortar layers were 22 lbs/ft (4 kN/m) and 5 lbs/ft (2 kN/m) respectively.

The higher value was obtained for test No. 10, in which the layer was loaded

with the maximum rate of loading, equivalent to an impact load. The incon

sistent differences shown by these results indicate that changes in the

rate of loading do not have a systematic influence in the structural be-

havior of the mortar layers or in the values of the maximum resistance.

3-82

3.6.6 THICKNESS OF THE LAYER

As previously explained, the same thickness of the mortar layer

was used for all tests in this preliminary program, therefore no special

tests were conducted to investigate its influence on the structural be

havior of the layer. The small variation of this value (3/4 to 1-1/2 in.)

between the mortar layers made it impossible to determine the effect of

thickness on the structural behavior of the layer. However, from the same

results obtained from these tests and knowledge of the structural behavior

of uniformly loaded beams, it can be concluded that the residual resistance

of the layers which follow type 2 and 3 curves, is directly proportional

to the third power of its thickness.

The influence of the mortar thickness on the maximum resistance

of the la}~r could not be established since all of the mortar layers ex

hibited the same mode of failure (adhesion).

3.7 CONCLUSIONS

3.7.l PERFORMANCE OF THE TESTING DEVICE

The performance of the test device was checked by careful ob

servation of the behavior of the apparatus and its effect on test results.

For example, in the first two tests mortar penetrated the slots surrounding

the movable block and thus altered the structural behavior and capacity of

the layer. It was decided, for future tests, to prevent penetration of

mortar in to these slots so that only the surface conditions and strength of

the mortar would be tested. This was accomplished by filling the slots with

3-83

a low frictional material such as cotton or a caulking compound. It was

also observed during these first two tests that the surface slabs were

displacing with respect to the fixed walls in a zone close to the movable

block. Additional bars tying these concrete slabs to the fixed walls were

provided to prevent this movement.

Forward movement of the fixed walls was monitored with dial gages

as explained in Section 2.4. After the first three tests additional pre

stress forces were applied to the fixed walls, reducing their forward move

ment to a negligible level.

After minor adjustments during the first few tests the device was

found to perform satisfactorily. The friction forces on the movable block

were less than 50 lbs (222.5 x 10-3 kN) when the block was displaced with

out a mortar layer present. There was no appreciable tilting or rctation

of the movable block and the rams used to apply the loads could be controlled

with sufficient accuracy.

3.7.2 SUMMARY OF THE EFFECTS OF THE VARIABLES ON THE STRUCTURAL BEHAVIOR OF THE LAYER

The same mode of failure--separation of the mortar layer from the

surface slabs--was present in all the tests carried out in this preliminary

program.

Two typical structural behaviors were observed for the mortar

layers tested. In both, a very stiff, elastic relationship existed be

tween the resistance of the layer and the displacements of the movable

block, before the maximum, or peak, resistance of the layer was reached.

3-84

However, for further displacements the resistance of the mortar layer in

one case dropped immediately to zero. This occurred in short layers and

layers not having boundaries ·and sufficient adhesion to provide end re

straint and development of a simply supported beam. In the other case,

the resistance of the mortar layer was gradually reduced with further dis

placement of the movable block. The post-maximum resistance offered by

the mortar layer has been called residual resistance.

The structural behavior of the mortar layers tested in this pre

liminary program was controlled by the lateral boundaries of the layer.

Whenever steel plates were used in the tests, a boundary to the adhesive

failure propagation was created, thus enabling the layer to behave as a

simply supported beam and to provide some residual resistance. When no

steel plates were used, the adhesive failure propagated in most cases to

the layer boundaries, producing an instantaneous failure.

The maximum resistance of the mortar layers was directly related

to: l) the strength of the mortar in the layer, 2) the adhesion character

istics of the surface slab, and 3) the length of the mortar layer on the

walls close to the movable block.

The residual resistance of the mortar layer depended mainly on:

1) the strength of the mortar, 2) reinforcement of the layer, 3) the length

of the beam, and 4) the thickness of the layer.

In the ranges tested, the rate of loading had no significant ef

fect on the peak or residual resistance of the mortar layers.

3-85

CHAPTER 4

SHOTCRETE TESTS

4.1 INTRODUCTION

For the shotcrete tests the same planar geometry of the testing

device was used. However, the methods of layer application were completely

revised; the necessary equipment for placing of the shotcrete had to be se

lected, prepared and tested. The preparation of the testing device and

testing of the applied shotcrete layers followed the same procedures used

for the testing of the mortar layers. The displacements of the shotcrete

layer and of the movable block were again measured by dial gages, but the

measurement of surface strains was discontinued for the reasons given in

Section 3.5.4. The same electronic recording instruments were utilized

for measurement of the load and displacement of the rams. The subsequent

data and results are presented in a manner similar to that used for the

mortar tests.

Measurement of the displacement occurring between the fixed wall

and the surface slabs were made during two of the shotcrete tests. This

relative displacement had not been measured in the mortar tests.

The variables studied during the shotcrete tests included all of

those investigated in the mortar tests; i.e., the effects of a change in

adhesion conditions, layer strength, reinforcement and boundary conditions

were investigated. In addition to these, the effect of the thickness of

the layer was also included.

4-1

l

4.2 SHOTCRETE OPERATION

4.2.l PREPARATION OF TESTING DEVICE

Prior to shooting, the testing device was prepared to: l) facili

tate the shooting operation, 2) set up the required test conditions, 3) fa

cilitate the preparation of the shotcrete layer for testing; and 4) mini

mize the effects of other variables on test results.

Several measures were taken to facilitate the shooting operation.

The entire testing device was surrounded by plywood wingwalls which would

confine the rebound to a sll)all area. These wingwalls are shown in Fig.

4.1 Vertical guide wires were placed to assist the nozzleman in spraying

the shotcrete to the required thickness. These wires were installed at dis

tances corresponding with the desired thickness of the layer. They can

be seen in Figs. 4.1 and 4.2. Finally, the floor in front of the test wall

was covered with canvas tarps to facilitate clean-up a.fter shooting.

The required adhesion cond~tion was obtained by preparing the

concrete surface slabs before shooting. For those tests in which a good

bond between the shotcrete and the slabs was desired, the surface of the

slabs was roughened with a wire brush. The re1 3tive roughness of the sur

face was then measured and recorded by the device discussed in Appendix B.

For those tests representing low adhesion, the slab surface was covered

with nylon filament tape. The entire area of the test (2 ft x 10 ft) in-'

eluding the movable block was covered with tape. The tape was cut along

the joints between the movable block and fixed wall. The tape-covered

strip can be seen across the upper movable block in Fig. 4.3.

4-2

l

FIGURE 4.1 FRONTAL VIEW OF TESTING DEVICE WITH PLYWOOD WINGWALLS

FIGURE 4.2 CLOSE-UP SHOWING VERTICAL SCREED WIRES AND TAPED SURFACE

4-3

FIGURE 4.3 FRONTAL VIEW OF COTTON-FILLED MOVABLE BLOCK-SURROUNDING SLOTS

The surface of the movable block was made flush with that of the

fixed wall to assure a uniform thickness of shotcrete.

To reduce the difficulty in removing excess shotcrete and dis

turbance to the shotcrete layer before testing, several measures were taken

before the shotcrete was applied . Filament tape or oil was used to cover

those areas of the wall where the shotcrete was to be removed. For tests

with fiber reinforced shotcrete, t he test strips were framed with wood boards

so that excess shotcrete could be removed without chiseling. This re

duced greatly the disturbance to the layer during trimming.

For many tests, steel plates were used as boundaries of the shot

crete layer. These plates were held by rods which passed through the wall,

the surface slab, and the shotcrete layer. Drilling of holes through the

4-4

shotcrete to accommodate these rods was avoided by extending the rods out

of the surface of the wall before shooting. The rods were then covered

with tape to preserve their threads.

To provide the same testing conditions except for the parameter

being studied, great care was taken in the preparation of the test wall.

The presence of shotcrete within the joints between the movable block and

fixed wall was eliminated by placing cotton in the open slots (see Fig.

4.3). To provide a uniform surface,the same type of tape and surface pre

paration were employed to minimize the variation of surface roughness, and,

therefore, its effect on testing.

4.2.2 SHOTCRETE MIX

All tests were conducted using dry-mix shotcrete. The same mix

proportions were used in all the shootings with the exception of test Nos.

15 and 16 in which fiber was added. The basic mix design is shown in Table

4.1.

TABLE 4.1

DRY MIX PROPORTIONS WITHOUT FIBER

Per 1/2 C.Y. Percent lbs (kg)

Sand 575 (261) 40.8

Gravel 575 ( 261) 40.8 Cement 250 ( 116) 17.8 Accelerator 7.5 (3.4) 0.6

4-5

The grain size distributions of the sand and gravel making up the

shotcrete are shown in Fig. 4.4. The uniformity coefficient of the sand

was 2.19 while that of the pea gravel was 1.41. The combined gradation

curve for the sand and gravel is also included in Fig. 4.4. Type l port

land cement was used along with Sigunite dry-powder accelerator. The ac

celerator was added in a proportion of 3 percent by weight of cement.

The mix design for test Nos. 15 and 16, in which fiber was used,

is shown in Table 4.2. The percent of fiber added was approximately 3 per

cent by weight and l percent by volume. U.S.S. Fibercon steel fiber, 0.010

in. x 0.022 in. x l in. (0.0254 cm x 0.0559 cm x 2.54 cm) was used in the mix.

Sand Gravel Cement Fiber Acee l era tor

TABLE 4.2

DRY MIX PROPORTIONS WITH FIBER

Per 1/2 C.Y. lbs (kg)

575 (261) 575 (261) 250 (116) 43 (19.5) 7.5 (3.4)

Percent

39.6 39.6 17.2 3.0 0.6

Water was added to the dry-mix materials at the nozzle. A pre

liminary measurement of the amount of water injected at the nozzle indi

cated that the water-cement ratio of the shotcrete as it left the nozzle

was approximately 0.50.

4-6

-

·-

-

U.S. STANDARD SIEVE NUMBER 4 • 2• 1-1/2" 1" .114" 1/2" 1/4" 4 6 I 10 12 16 ZO JO 40 !10 10 100 140 200 270 400

,oo • 11 I i I' i ■'r"'"',.. ' i ' i i ' ' _'._Jl.11.f'.LLL I II 111 I I I I lo , 0 '- fTI I I I I I 111111 I I I 110

' 1111 1 I I I

,o "-.~ . - I I I I I I 120

- r-Sand /i I ~

7011 t I I I I I I 111 I I I I I I I 1111 I +-+-+·--+ • v I -- t-

' IJ J: ~ 1: 1 r t , ; 1 ,, l'1 - ~- u ----· ·--~- ---~--- !:? Cl 60 ·-- -- 40 w ii:j I I ! ' : • - - ._ ----~-- - - ·---·· -- ·-·--· H- -~ -- --~------ ~-~- - --·- -- ~ ► . \.. , I I

; E ·-· -- :--::_~ rt-==- ! r--~ -- -J - - +t- - - - --~~- - EI f •o - . .!.: ___ ~) t' ~ · ' 1 +--~ _.__, Combined - .... • ·· -- --- eo u

. I I : I I . 'I I ---- '\ V I ... t . . l ·+1 • . ~ ..... \,I + II I ...

~ - rt H:_ -. i~-~--1 i i·'-'-Gra~el_/ •-~-._ ··-:-:=_ ~~ ~ \ ·-=- ·---- tf""" _ ....... ~'""t·.. ~=-=-= 1C; ~ ~~ ~~-i --~ I ---- hi}~ --± -- l"I .. , 1 -- - ·-· I i . ~ -~ . - '·-r- ,•· -- --- D..

10ftf ~= ~ = =-= tt~=~ ~- ___ ___ _ \ . I I __ -_ _ j-~- ----- eo ·: i , ,\ I

10-tt- · I - ~ ;j I I r'-. ~

I I I I i-+++--+-+-· ---190

;· ~ - 1 Ii 1 11 -;-i:..._ -- 1 I 11'.. JI Iii I ,I I , I I 111 I I I I I I I

0 -1000 SO() 100 50 10 5 ,0 1.0 0 .5 0 ,I 0 .05 0.01 0 .00, 0 .00f GRAIN SIZE IN MILLIMETERS

LW'IED COBBLES SILT or CLAY

MIT CLAY

Toroedo sand: eea gr:alle] :

Natural water content: 10. 0% N;:it11r;:i l w;:i h::>r r nntont • l 7 °L % Passinq #200 sieve: 1.0% % Laraer than 3/8 11 (ln mm) l O'¼ D60/D10 = 2.19 060/D10 = 1.41 · -

-· ·-------

FIG. 4. 4 GRADATION CURVES.

4.2.3 EQUIPMENT

The equipment used to place shotcrete consisted of a mixer, a

belt conveyor, and a dry-mix shotcrete machine. The mixer was an electric,

rotating drum type mixer having a 1/2 C.Y. (0.382 m3) capacity. The ma

terial, after leaving the mixer, was conveyed to the gun by a gasoline

powered, belt conveyor. The gun, a Reed Model LASC II, was used to spray

the shotcrete onto the surface of the model. The material was conveyed

to the nozzle in a 2 in. (5.08 cm) diameter hose having a length of 100

ft (30.4 m). A stepped-balloon nozzle having a length of 1 ft was used

to direct the material onto the wall. The water was delivered by an

ordinary garden hose and regulated by a screw valve at the nozzle. The

water ring had an inside diameter of 2-1/2 in. (6.35 cm) and contained

four holes 3/16 in. (0.476 cm) in diameter, symmetrically placed around

it. A photograph of the nozzle can be seen in Fig. 4.5. The arrange

ment of the equipment is shown schematically in Fig. 4.6, and pictured in

Figs. 4.7 and 4.8. In both Figs. 4.7 and 4.8, the shotcrete machine is

shown at the extreme left.

In the first several tests, the accelerator was added at the

gun using a screw-feed accelerator dispensor. However, difficulty in the

operation of this device made it necessary to manually add the accelerator

to the material as it passed on the conveyor.

4.2.4 SHOOTING PROCESS

Since the mixer had only a 1/2 C.Y. (0.382 m3) capacity, the

4-8

FIGURE 4.5 NOZZLE CLOSE-UP

4-9

~ I __,

0

Sand Gravel Cement (Fiber)

aterial

\. Mixer -'

-

Acee 1 era tor Air-pressure Water

Sho.tcrete - Conveyor Gun Hose Nozzle --

FIGURE 4.6 SCHEMATIC ARRANGEMENT OF THE SHOTCRETE EQUIPMENT

FIGURE 4.7 ARRANGEMENT OF SHOOTING EQUIPMENT

FIGURE 4.8 CLOSE-UP VIEW OF BELT CONVEYOR AND POWERED GUN

4-11

shotcrete had to be prepa red in several batches. To provide a nearly

continuous shooting operation, the material for each batch was pre-weighed

and stored in drums. Thi s assured a minimum batching time dur ing gunning

of the model.

For each batch the required amounts of sand, gravel, cement, and,

for test Nos. S-15 and S-16, fi ber were loaded into the skip and then dumped

simultaneously into the mi xer. When fiber was added, a sieve with 1 in.

(2.54 cm) square opening wa s used, as shown in Fig. 4.9, to break up any

entangled balls of fi ber . The batched materials were always mi xed a

minimum of 3 minutes. The ra t e of material transported to the gu n was con

trolled by the speed of the con veyor and was set so that the time of the

material in the hopper remained ess entially the same. The accelerator was

manually added onto the conveyor.

The first batch was gunned against a plywood practi ce wall, as

shown in Fig. 4.10, which was located away from the testing device . This

allowed the nozzleman and gunman to adjust the air pressure and r otation

speed of the machine so that a smooth, continuous flow of ma ter ial would

be delivered to the nozzle whi le shooting the surface of the model. During

th i s time a 2 ft x 2 ft x 3 i n. (61 .0 cm x 61 .0 cm x 7.62 cm) test panel

was also gunned to obtain sampl es fo r strength tests. An empty test panel

is shown in Fig. 4.10, the shooting of the test panel is shown in Fig. 4.11,

and a filled panel is shown in Fig . 4 .12.

After the complet i on of the practice shooting, the shooting oper

ation was then moved to the test wall. The wall was first cl eaned using an

air-water jet from t he no zz l e. This removed any dust accumul ated on the

4-12

FIGURE 4.9 FIBER SCREENING USING 1-IN. (2.54 CM) SIZE SIEVE

FIGURE 4.10 WARM-UP SHOOTING AGAINST PLYWOOD WALL

4-13

FIGURE 4. 11 STRENGTH-SPE CIMENS PANEL BEING FILLED UP

FIGURE 4. 12 FINISH ED STRENGTH-SPECIMENS PANEL

4-14

surface of the slabs and prepared them for receiving shotcrete. The first

material delivered to the nozzle was shot against one of the wingwalls so

that the air pressure and water could be adjusted without placing poor

quality shotcrete. After these adjustments were made, the stream of ma

terial was directed against the test wall surface. The shooting began in

the lower right corner of the test wall and followed the path shown in

Fig. 4.13. The nozzleman used the guide wires to obtain a uniform thick

ness. For all shootings,the shotcrete was placed in a single layer. How

ever, additional materials were placed over indentations in the first

layer to obtain a relatively uniform thickness. The time between the

shooting of the first layer and patching of thin areas never exceeded 30

minutes.

FIGURE 4.13 PATTERN OF SHOOTING

4-15

During shooting, the air pressure at the gun ranged from 60 to

75 psi (4.22 to 5.27 kg/cm2). These pressures produced a material delivery

rate (including water) of 400 ·to 450 lbs/min (181 to 204 kg/min). The same

air pressure was used for all shootings in order to obtain approximately

the same compaction and thus the same strength in all of the tests. The

rate of water flow to the nozzle during one shooting was approximately 24.0

to 27.0 gal/min (1.51 to 1.70 l /min).

After the entire wall was covered with a layer of shotcrete, a

second test panel was gunned. This panel, like the first, was used to ob

tain samples for strength tests which were performed simultaneously with

the large scale test. In addition, for test Nos. S-13 to S-16, another test

panel was shot to obtain samples for adhesion tests. For test Nos. S-13 and

S-14, a 1-ft x 1-ft x 3-in. (30.5 cm x 30.5 cm x 7.62 cm) concrete slab was

used for the adhesion test panel. To reduce the difficulty of cutting the

adhesion test samples, a concrete slab was pre-cut to the desired sample

size. A 4 x 6 array of 2 in. x 2 in. x 3 in. deep (5.08 cm x 5.08 cm x

7.62 cm) concrete blocks, joined together by brittle plaster, was used for

test Nos. S-15 and S-16. The shotcrete-slab adhesion samples were procured

by cutting only the shotcrete l ayer. This procedure permitted samples to be

obtained for early adhesion tests.

4.2.5 CURING

Immediately after the shooting, the plywood wingwalls were removed

and the shotcrete layer was trimmed around the top and bottom of each mov

able block and fixed wall slabs. For all tests, except those containing

4-16

steel fibers, the trimming was accomplished by chiseling along the bound

aries of the test layer. The removal of the surrounding material was facil

itated by placing the tape or oil on those areas to be trimmed. For the

steel fiber shotcrete tests, boards were placed horizontally along the ex

treme upper and lower boundaries of the layers. These boards were easily

removed and an evenly trimmed edge was obtained. Only the 3-in. (7.62-cm)

wide strip between the two test layers had to be removed using a hammer

and chisel. The guide wires were left embedded in the shotcrete to avoid

disturbance to the test layer. Figure 4.14 shows a non-fiber reinforced

shotcrete layer after it was trimmed.

After trimming, burlap was placed over the shotcrete layer and ,

moistened. The burlap was then covered with plastic sheets to retain the

moisture. Periodically the burlap was rewetted to provide a constant moist

curing environment for the shotcrete. A photo of burlap and plastic placed

over test layers can be seen in Fig. 4.15.

The 2-ft x 2-ft x 3-in. (61.0 cm x 61.0 cm x 7.62 cm) shotcrete

panels were placed in a concrete curing room in which humidity and tem

perature conditions were similar to those surrounding the shotcrete in the

model. Panels were kept in the room until it was time for preparation and

testing.

The adhesion test panels were covered and cured in the same manner

as shotcrete on the test wall; they were covered with burlap and plastic, and

periodically moistened. This was done so that the adhesion of the test speci

mens would match as closely as possible that existing on the test wall.

These panels were also cured unt i l just before testing.

4-17

FIGURE 4.14 FRONTAL VIEW OF SHOTCRETE LAYERS IMMEDIATELY AFTER TRIMMING

FIGURE 4.15 FRONTAL VIEW OF SHOTCRETE LAYERS DURING CURING PROCESS

4-18

4.3 SHOTCRETE TEST PROGRAM

The shotcrete test program was set up using the same hypotheti

cal model of thin layer behavior shown in Fig. 3.5. Based on the results

of the mortar tests, modes of failure were predicted for the shotcrete

layers. The same variables, but including reinforcement, were reassessed

in terms of the structural behavior of shotcrete rather than mortar.

All shotcrete layers covered the full width of the model. This

application assured that adhesive stress would be fully mobilized along

the portion of the fixed walls bordering the movable block. In addition,

full coverage of the surface of the model permitted a wide range in the

spacing between the steel plates which formed the lateral boundaries of

the layer. For all tests a loading rate of 5 lbs/sec (22.2 N/sec) was

used in applying the load from the ram to the movable blocks.

The parameters selected for study in the shotcrete tests in

cluded: 1) lateral boundaries of the layer, 2) adhesive strength, 3)

shotcrete strength, 4) thickness of the shotcrete layer, and 5) rein

forcement. The manner in which these parameters were varied and the

values assigned to them in the 16 shotcrete tests are summarized in

Table 4.3 and described in the following sections.


In most tests the lateral boundaries of the shotcrete layers were

established by steel plates simulating rock bolts or boundaries of openings

in actual tunnels. Steel plates were not used in five of the shotcrete

tests (test Nos. S-1, S-2, S-3, S-5 and S-7 - Table 4.3) This case

4-19

TABLE 4.3

MATERIAL PROPERTIES OF SHOTCRETE LAYERS

COLUMNS 1 2 3 4 5 6 7 8

Comp. Flexural E Rock bolt Test Thickness Adhesion strength strength

106psi/GPa Length at

no. in./mm psi/kPa psi/MPa psi/MPa in./m ft/m

S-1 1.82 180 3580 565 3.64 48 None 46.23 1241 24.7 3.9 25.10 1.22

S-2 1.70 180 3580 565 3.64 48 None . 43.18 1241 24.7 3.9 25.10 1.22

S-3 2.18 187 4890 3.08 48 None 55.37 1289 33.7 21.2 1.22

S-4 2. 11 20 4890 3.08 48 8 53.59 138 33.7 21.2 1.22 2.44

S-5 5.26 185 3830 740 4.70 48 None 133. 60 1276 26.4 · 5. l 32.4 1.22

S-6 4.70 20 3830 740 4.70 48 8 119.38 138 26.4 5. 1 32.4 1.22 2.44

S-7 2.78 60 910 250 2.30 48 None 70.61 470 6.3 1.7 15.9 1.22 2.44

S-8 2.95 10 910 250 2.30 48 8 74.93 69 6.3 1.7 15. 9 1.22 2.44

S-9 2.65 154 2400 450 3.70 48 4 67.31 1062 16.5 3. 1 25.5 1.22 1.22

S-10 3.07 37 2400 450 3.70 48 4 77.98 255 16.5 3. 1 25.5 1.22 1.22

S-11 5.24 45 718 80 0.86 48 8 133. 10 310 5.0 0.3 5.9 1.22 2.44

S:-12 5.46 20 718 80 0.86 48 8 138.68 138 5.0 0.3 5.9 1.22 2.44

S-13 1.80 185 2850 141 7.34 48 8 45. 72 1276 19.7 1.0 50.6 1.22 2.44

S-14 1.06 187 2850 141 7.34 48 8 nr "" 1;:o::, I~•/ Lu 50.6 1.22 2.44 c..v. "3C.

S-15 3.66 3450 930 48 8 92.96 23.8 6.4 1.22 2.44

S-16 4.43 3450 · 930 48 8 112. 52 23.8 6.4 1.22 2.44

4-20

would represent a tunnel in which bolts were not installed or were placed

only locally. In nine of the tests, Nos. S-4, S-6, S-8 and S-11 to S-16,

the steel plates were located at 8 ft (243.2 cm) apart. Finally, for two

of the shotcrete layers tested, Nos. 9 and 10, the distance between the

steel plates was equal to 4 ft (121.6 cm) or l ft (30.4 cm) from the edge

of the movable block.

These steel plates were used to provide a restriction to propa

gation of an adhesion failure and to evaluate the residual resistance of

the layer acting as a beam. Variation in the spacing of the steel plates

was not expected to have an effect on mode of failure or the maximum

res istance of the shotcrete layer.

4.3.2 SH0TCRETE STRENGTH

The variation in shotcrete strength was obtained by testing the

layers at different times after application of the shotcrete.

The strength of the shotcrete in the layer was estimated by per

forming standard compression and flexural tests on shotcrete specimens ob

tained from the sample panels. These tests were conducted at approximately

the same time as the model tests and were used for strength control. In

some of the model tests, strength tests were also carried out on shotcrete

samples cut from the failed shotcrete layer. A comparison of the strength

results from the two sets of samples indicates that the shotcrete in the

panel is representative of the shotcrete placed on the surface of the

model. Columns 4, 5 and 6 of Table 4.3 show the compressive and flexural

strengths and the initial tangent modulus of the shotcr ete in the test panels.

4-21

The average values of adhesive strength for shotcrete cured 7 days varied

from 180 psi (1241 KPa) for roughened surface slabs to 20 psi (138 KPa)

for the surface slabs covered with filament tape. When the shotcrete was

cured for 7 hours, the average values of adhesive strength ranged between

77 psi (531 KPa) and 10 psi (69 KPa).

The variation in adhesive strength with time of curing repre

sented by the unconfined compressive strength and surface conditions is

shown in Fig. 4.18. In this figure the average values of the adhesive

strength for both the roughened and taped surfaces are plotted against

the compressive strength of the shotcrete. The greatest difference in

adhesive strength occurred between samples having roughened concrete and

taped surfaces at 7 days and between samples having rough surfaces but

tested at 7 days and 7 hours. The test results further show that adhesive

strength is insensitive to time of curing for poor bonding conditions.

The adhesive strength of the shotcrete on the roughened concrete surfaces

was approximately twice that on the taped surfaces at 7 hours.

The tensile load vs deformation data obtained from the adhesive

tests indicate that the stiffness .in adhesion is very high and that the

mode of failure is very brittle (Fig. 3 - Appendix C). Almost no dis

placement occurred at the contact during the loading process before failure,

and after failure had occurred the resistance immediately dropped to zero.

Finally, the adhesion failure did not always occur along the

shotGrete-concrete contact but sometimes took place along laminations in

the shotcrete. The adhesive strength values obtained in these cases were

not used in computing the average adhesive strength of the layer.

4-22

The compressive strength of the shotcrete varied from a maximum

of 4890 psi (33.7 MPa), in test Nos. S-3 and S-4, to 718 psi (5.0 MPa) in test

Nos. 11 and 12. Variations in the strength of shotcrete having approxi

mately the same curing time are related to variations in the shooting pro

cess and in its ingredients.

4.3.3 ADHESIVE STRENGTH

The adhesive strength between the shotcrete and concrete surface

slabs covering the walls was varied directly by changing the adhesive char

acteristics of the surface slabs, and indirectly by varying the shotcrete

strength.

Column 3 in Table 4.3 shows the average values of the adhesive

strength between the shotcrete layers and the surface slabs obtained from

the tests on the 2-in. x 2-in. x 6-in. (5.08-cm x 5.08-cm x 15.2-cm) sam

ples cut from sections of the test layer. In most of the cases, the sam

ples were taken from either the slab on the movable block or from locations

close to the edge of the fixed walls where little or no disturbance of the

layer took place during testing. Figure 4.16 shows a typical facing slab

covered with shotcrete from which the adhesion test specimens were cut.

The samples were prepared so that the interface between the shotcrete and

concrete slab was located in the middle of the prism.

The test apparatus used, the procedure followed, and all of the

results obtained in the adhesion testing program are described and sum

marized in Appendix C.

4-23

FIGURE 4.16 COMBINED SHOTCRETE-SLAB SECTION AND CORRESPONDENT ADHESIVE TEST SAMPLES

FIGURE 4.17 ADHESIVE TEST SAMPLES AFTER TESTING

4-24

0 0

0 0

Adhesive strength, kPa 0

0 0 0 0 0 0

0 0 0 0 0 0 N c;:t- I.O

0 N ..t- I.O co ~

I 8-----...------,-------,-------,--------, 0 co

0 0 0 r---

0 0 0 I.O

0 0 0

. ,... LO 1/)

Cl.

..r::::. +> CJ')

C Q.) 0 s.. 0 +> 0 1/) c;:t-

Q.)

> ...... Vl Vl Q.)

s.. Cl. E o O 0

U 0 M

0 0 0 N

,,,,,,.-....... ( .4 '\ \ \ \ \ I I I I

I I I I I I I I

1, 10• I __ / 7 hours taped surface

7 days taped surface

--........ / ( .3 \ \ \ \ I I I I I 1 •s I

/ •1•2 / I I

I I I I

/ 13" / / 14;

I I l •9 / , __ ..,,/

7 days roughene surface

g _/ ---, /As \ /- 7 ■ ' 7 hours

roughened surface

\ •12 \ t• 11 .,) , __ ; ...... __ _ Oo!,------,.,..-----,.,..-----,.,..-----:0"":--------;,!o

0 LO 0 LO N N

Adhesive strength, psi

FIGURE 4.18 ADHESIVE STRENGTH VS COMPRESSIVE STRENGTH OF THE SHOTCRETE LAYERS

4-25

0 0 co

LO LO

0 LO

LO M

~

..r::::. 0 +> M C'>

C Q.)

s.. +> Vl

LO QJ N > ......

Vl Vl Q.)

s.. Cl. E

0 0 NU

Lt')

0

LO

0


Column 2 in Table 4.3 shows the average thicknesses of the shot

crete layers. These thicknesses are typical of those used in practice for

thin linings, and ranged from a maximum of 5.46 in. (13.9 cm) in test No.

S-12 to a minimum of l .06 in. (2.69 cm) in test No. S-14. These values

represent the average thickness measured along the failure cracks in the

layer. The measurements show a remarkable uniformity in the thickness of

all the layers shot (±0.l in.) (0.254 cm).

4.3.5 USE OF REINFORCEMENT

Two of the tests, Nos. S-15 and S-16, were conducted on shotcrete

containing steel fibers, 1-in. x 0.010 in. x 0.022 in. (2.54-cm x 0.254 mm x

0.559 mm). In each test 144 lbs (65.3 kgms) of steel fiber corresponding to

3 percent by weight or percent by volume of the entire batch were added to

the mix.

The presence of steel fibers added to the materials in the above

proportions has been shown to increase the tensile strength of the shotcrete

(Parker, et al., 1975) or at least improve its ductility. It was therefore

expected that reinforcing with the steel fiber would affect the residual re

sistance of the shotcrete layer without changing its mode of failure or maxi

mum resistance.

4.4 TEST RESULTS

The shotcrete layer test results were plotted and analyzed in the

same manner as those obtained in mortar tests. The load in the jack repre-

4-26

senting the resistance of the shotcrete layer was plotted against the 11 net 11

displacement of the movable block. The relative forward displacement of the

shotcrete layer was obtained for each load increment by subtracting the dis

placement of the 11 fixed 11 walls of the test device with respect to the floor.

The displacement of the wall was quite small (0.001 in.; 0.025 mm) compared

with the displacement of the movable block.

4.4. l MODES OF FAILURE

The two basic modes of failure shown in the conceptual model in

Section 3.3 were observed in the shotcrete layers. Column 2 of Table 4.4

shows the mode of failure for each shotcrete test.

A diagonal tension failure occurred in tests S-1, S-2, S-13 and S-14.

(Fig. 4.19).

FIGURE 4.19 FRONTAL VIEW OF FAILED SURFACES IN TEST NOS. l AND 2

4-27

TABLE 4.4

SHOTCRETE LAYER TEST RESULTS

COLUMNS 1 2 3 4 5 6 7 8 9 10 11

Length Length of of

Max. t,_ Residua 1 t,_ develop develop I EI Curing Test Failure load failure 1 oad residua l ( 1 eft) (right)

. 4; 4 106. 4; 4 time

no. mode 1 bf / kN in./mm l bf /kN in./mm in./m in./m 1n . cm ,n. m hrs

S-1 Shear 15,250 0.01 0 0.10 9 30 12.06 43.9 72 67 .8 0.25 0 2.54 0.2 0.8 502.0 18.3

S-2 Adhesion 13 ,250 0.01 0 0.15 5 3 9.83 35.8 72 -Shear 58.9 0.25 0 3.81 0. l 0.08 409.2 14.9

S-3 Adhesion 17.375 0.02 2800 0.06 48 15-1/2 20.72 63.8 144 77 .3 0.51 12.5 1.52 1.2 0.4 862.4 25.6

S-4 Adhesion 2,500 0. 01 2600 0.04 36 36 18.79 57.9 144 -Bending 11. 1 0.25 11.6 1.02 0.9 0.9 782. l 24.1

S-5 Adhesion 17,500 0.04 0 0.04 48 48 . 291.06 1368.0 168 77 .8 1.02 0 1.02 1. 2 1.2 12114 .8 569 .4

S-6 Ad hes ion 4,550 0.03 3200 0. 12 36 3b 207.65 975.9 168 -Bending 20.2 0.76 14.2 3.05 0.9 0.9 8643.0 406.2

S-7 Adhesion 5.500 0.02 5200 0.27 24 48 42.97 98.8 7 24 . 5 0 .51 23. 1 6.89 0.6 1.2 . 1788. 5 41. l

S-8 Adhesion 1,700 0. 01 500 0.15 36 36 51.34 118. 1 7 -Bending 7.6 0. 25 2.2 3.81 0.9 0.9 2136.9 49.2

S-9 Adhesion 20,250 0.03 0 0.50 12 12 37.22 137. 7 144 -Bending 90. 1 0.76 0 12 .70 0.3 0.3 1549.2 57.3

S-10 Adhesion 7,000 0.06 6960 0.30 12 12 57.87 214.l 168 -Bending 31. 1 1.52 31.0 7.62 0.3 0.3 2408.7 89.l

S-11 Adhesion 6,620 0.02 2970 0.05 36 36 287.76 247.5 7 29.4 0. 51 13.2 1.27 0.9 0.9 11977 .4 103.0

S-12 Adhesion 2,640 0.02 1300 0. 10 36 36 325.54 280.0 7 11 .7 0. 51 57.8 2.54 0.6 0.6 13550.0 116 .5

S-13 Shear 19,930 0.07 0 0.08 9 12 11.66 85.6 192 88.7 1.78 0 2.03 0.2 0.3 485.3 35.6

S-14 Shear 7,250 0. 01 350 0.04 7 7 2.38 17.5 192 32.2 0.25 1.6 1.02 0.2 0.2 99. l 7. 3

S-i5 Auite!; i Uri 14 ,.JI:> u. 10 38<+0 0.36 8 3 i68 -Bending 63.9 4. 06 17 . 1 9. 14 0.2 0.08

S-16 Adhesion 4 ,100 0.08 1440 0.45 48 48 168 -: Bend i ng 18 .2 2.03 6.4 11 .43 1.2 1.2

4-28

The type l curve is characteristic of diagonal tensile failures

in which an immediate and complete reduction of layer resistance was ob

served after failure (test Nos. S-1, S-2, S-13 and S-14). A similar be

havior is shown by the type 2 curve, typical of test Nos. S-3, S-5 and S-7,

in which no steel plates were used and the adhesive failure propagated at

least on one side to the margins of the layer. Once the maximum resistance

of the layer was reached, however, it was held temporarily during additional

displacement (up to 0.05 in.) of the movable block.

The type 3 and 3A curves reflect the structural behavior of the

remaining layers. In these layers an adhesive failure initially developed

between the shotcrete and the surface slab. However, the steel plates on

the fixed block limited the lateral extent of this adhesion failure and

allowed t ;,e layer to behave as a beam.

The character of the residual resistance shown by the 3 and 3A

curves depends on the ductility and flexural strength of the shotcrete

layer as well as the spacing between the steel plates. The type 3A curve

is typical of the results obtained from tests in which shotcrete was placed

against filament tape (low bond strength). The presence of the tape re

duced the adhesive strength, therefore decreasing the maximum resistance of

the layer. In this case the adhesive strength was nearly the same as the

bending capacity of the layer. Type 3 curves were obtained when shotcrete

was in contact with roughened concrete.

The resistance-displacement relationships for all the shotcrete

tests are shown in Figs. 4.21 to 4.28. The maximum resistance and block

4-29

(/)

I-z: LLJ ::::E: LLJ u ex:: ...J 0.. (/) ..... Cl

~ u 0 ...J

V') c::i +-> LLJ c:: Q) ...J E c::i Q) ex:: u > rt! 0 ,- ::::E: c..

(/) V') ..... > -c:,

LLJ ~ u u :z: 0 ex::

I ,- I-..0 l '1

I .....

Q) (/)

I ,- LLJ ..0 ~

/ ~ :::c > / 0 I-

::::E: <.!J z: LLJ ...J

I-..... z: :::,

0 N

G .

<::I'"

LLJ ~ :::, <.!J ..... LL

0

4-30

-Movable block displacements (rm1)

0 0.25 0.50 o. 75 l I OQ 1. 25 1.50 1. 75 2.00 I I I I I I I I I -,90

500 I I I I -·• 80 __

C: ' .... E ......... ......... 4- z: .&:I ~ ,- -- 400 70

Shotcrete +' +J u V 11' _.,,

~Scale I +' +J C:

C 0 ·o 2'0 in·. 60

u ·v 4-.... 0

()

300 ..c .c +' +J

50 Ol ' t:n C:

i Q) ,--+J +' .... ·- 40 C:

C :::, ~ - ::,: I , s...

w L Q) __, a, 0. ~

30 Q)

a, u u C: C 11' It! +' +J 1/) VI •,-....

20 1/)

VI Q)

~ 100 c:::

10

0 .__ _ _._......., ____ ......_ ___ __. ________ ---' ____ ...._ _________ __.

0 10 20 30 40 50 60 70 80 0


FIGURE 4.21 UNIT LENGTH RESISTANCE VS KJVABL£ BLOCK DISPLACEMENTS

Movable block displacements (nm) 0 0.25 0.50 0.75 1·, 00 JI 25 J,ro l. 75 2.00 I I I I I I I 90 -,

500

I I I I I I •

£, 1~4 i~-~tc!i Jack I

,}(4 ;~~ I 80

I .q««tp«««<<«««<«y I ''""''"""""'1P"'"l fot' I I -. C:

'112' ¥73WIWTiiW ilCi 'f tf:4 1•·•,::-li llt:31• ·· '@I ~ ·- 70 E ......... 400 ......... .....

0 Shotcrete z .J:I ~ _. - ...._;,

1~ca le., .µ .µ u u 20 in. 60 tO l'CS .µ .µ

C: C: 0 0 u u 300 ..... .....

0 50 0

.c: .c:

.µ .µ O'l O'l C: C: Q) Q)

40 _. _. ~ .µ I .µ

200 •r-w .,... C: N C: ::, ::,

s.. 30 s.. Q) Q) 0.. .. 0..

Q) Q) rS-4 u u 0 C: C:

tO ,a 100 .µ .µ

V) V) .,... .,... V) V) Q) Q)

10 c::: c:::

00 10 20 30 40 50 60 70 80

Movable block displacement (10- 3 in.) FIGURE 4.22 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS

-

- Movable block displacements (mm) 0 0.5 ],Q 1.5 2.Q ,-~ 3,Q 3,5 410

' I I I I I I -,90 500

I 1/4 11

Jack /St.pl. for I -----130

........ t J;.,, ,,,,,., .. J,. .t;J't~~:±~ S-6 ........ . E C '-.....

70 . ~ :;:- 400 S-5 ...,_... ..c ,--......,. +)

,~cal~ u tO +) +) - u 20 in. 60 C: ro 0 +) u C

0 . It--u 300 0 4-

50 .c 0 +) 0, .c C +) QJ Ol

C ,....

QJ

0 +) .i:::, ,-- .,... I

C: w +) 200 ::, w ..... C s.. ::,

QJ

30 0. s... QJ

Q) 0. u S-6 C QJ tO u +) - C 20 Ill ro ..... +) 100 Ill Ill QJ .....

0::: Ill QJ

0::: -- l.J -110 ---- --------.- -~ - -- ....

0 160 - 0 0 60 80 l 00 120 140

Movabl e block disp lacemen t s (10-3 in.)

FIGURE 4.23 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS .._.

.-

Movable block displacements (nm)

0 2.5 5. 0 7.5 10 .0 12.5 15.0 17. 5 20.0 I

90 -500 I I I I I

1!1~ i~~ I I I I 1/4 in. St~ £, ~-·- r n ack

80 . - q::::r+,iL.[~] ~~~ . -C: E .,...

....... ....... il 400 70 z

~ ,- o Shotcrete -: - - +J +J

1~ca 1 e--1 u

u ,a n, ' 20 in. 60 +J +J C: C: 0 0 u u . '+-

'+- 300 0 0 50 .&::.

.&::. +J +J en en C: C: cu cu ,-,-

40 +J ~ I +J .,-

w .... ,- C: ~ § 200 :::,

s.. s.. cu cu 30 c.. c.. S-7 cu .... cu u u C: C: ,a

+J n, 20 VI +J

-~ 100 .... VI cu Vl S-8 0:: cu

0::

10

0 100 200 300 400 500 600 700 800


- FIGURE 4.24 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS

- Movable block displacement (mm)

0 2.5 5.0 7.5 10.0 12.5 15 .0 17.5 20.0 I I I I I I I I I 790 500, I I I I 1 1/4" Steel~ I 1 /4" I r nl :.+o .l::ir-L- /<:.+ ... ,

80 I //VU.,,<««<<<""""'f ~ .

I r'"''««««<O:?'"~ I I -. C: .,... • ......... --r- to- ~ShotcrTte 70 E 4--

.CJ ......... z ,.... ........ ~

1~cal ~I ..__..

~ u .µ - "'

20 in. 60 u ~ "' C:

.µ

0 . i:::

u 0 u

S-9 4-- 4--0 50 0

.s= ~

..i:::

O') .µ

C C"l

QJ

' i:::

.J:::, ,.... 40 QJ

' ,....

I ~ w .,... 200

' .µ

c.n §

.... ' i::: ....... :::,

s... .._ ..._ 30 8.

s...

--- QJ c..

QJ u QJ

C u - ,a 20 i:::

~ "' "'

.µ Vl .....

"' .,...

QJ Ill

~ QJ

10 ~

0 -1'

0 100 200 300 400 500 0

600 700 800 Movable block displacements (lo-3 in.)


-

--

-

--

-

Movable block displacements (rm,)

0 0.5 l.O 1.5 2.0 2.5 3.0 3.5 4.0

soo-------------------------.,....--------------

..i::,. ·

---C

•,-......... ~ 400 ,-. -.µ u ltl .µ C 0 u

'+- 300 0

..c .µ O'> C QJ

,-.

I .µ w •,-0) • § 200

s... QJ C.

QJ u C: ltl .µ VI . ,-VI QJ

er:::

20

0

S-11

40 60 80 100 120



Shotcrete

,Ecal~I 20 in .

140 160

90

80

70

60

50

40

30

20

10

0

---E

----z ~

.µ u <ti .µ C: 0 u 4-0

..c .µ 0, C Q)

,-.

.µ •r-e ::::,

s... Q) C.

Q) u C <ti .µ Vl .,... Vl Q)

er:::


0 0.5 l.O 1.5 2.0 2.5 3.0 3.5 4.0 ::,...

90 500

I I I ; 1/4 in. I r!~4-~nt I I I

~ Jack C' ♦ - ,

80 ..-.... q::::r .. t .. r;:o ,..... .

E C: ........ •r-

70 z - 400 ~ 4- ...._., .D o Shotcrete ,-

+-' .__..

1~ca l e ..

1 u ,0 +-'

+-' u 20 in. 60 C tO 0 +-' u C:

0 4-u 300 0 4-

50 ..r:: ...... 0 +-' Ol .c C .µ Q) Ol

C: ,-

+'> Q) 40 +-' ,-

•r-I C w +-' ::, --.J •r- 200 S-13 - C: ~ ::, Q)

30 0.. s... <l)

Q) 0. u C Q) l,:J u +-' C: 20 VI It!

~S-14 ..... .µ 100 VI VI Q) •r-

0::: VI <l)

0::: ■ _I " . ., 0

0 - -20 40 60 80 100 120 140 160

Movab le block displacements (l0-3 in.)

-· FIGURE 4.27 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS

...

...

.... 0 2.5

I I 500

-. s:::

•r-....... 4-..c 400 .-

+.> u co

+-' s::: 0 u - 4-0

.i:,,. .s::. I +-'

w O'l co s:::

Q) .....

-- +-' •r-s::: ::::,

s.. Q) a. Q) u C: co

+-' Vl

•r-Vl Q)

0::: I I ~

5.0

I

Movable block displatemen~s (11111)

7.5 10.0 12.5

I I I

-·--

S-15

S-16

"'" -' - ---

500

Movable block displacements (10-3 in.)

15.0

I

I . I o -·

-~--


17.5 20.0

I I 90

80 -E ....... z ~

70 -+.> u C0

+.> C:

60 0

iScal H u 4-~o in. 0

.s::. 50 +.>

O'l C: Q) .....

+.> 40 •r-

C: :::,

s-Q) c..

30 Q) u C: ,,;

+.> Ill

20 •r-Ill Q)

ar::

I I

10

0

displacement obtained in each test are summarized in Table 4.4. Column 5

of the same table shows the value of the residual resistance after the ad

hesive failure reached its lateral boundary.

From the values given in Table 4.4, and the curves shown in Figs.

4.21 to 4.28, the following preliminary conclusions regarding the structural

behavior of the shotcrete layers can be drawn.

1. The movable block displacement at which the maximum

resistance of the shotcrete layers was developed varied

between 0.01 to 0.16 in. (0.25 to 4.06 mm).

2. When failure occurred by separation of the shotcrete

layer from the surface slab and no steel plates were

present, the resistance remained at the maximum value as

the separation gradually progressed outward. In these

cases the movable block reached maximum displacements

ranging between 0.04 in. (test No.S-5) and 0.3 in. (test

No. S-3)(0.10 cm and 0.76 cm) without collapse of the

shotcrete layer. This additional displacement of the

movable block indicates certain ductility in the be

havior of a thin shotcrete layer. This 11 ductility 11

depends on the adhesive strength along the total area

of contact between the shotcrete layer and the surface

slab and, more importantly, on the stiffness of the

shotcrete layer.

3. Residual resistances ranging from 30 to 100 percent of

the maximum layer resistance were observed depending on

4-39

•

the position of the boundaries, the shotcrete-slab

bond and on the flexural strength of the layer. In

these tests, the residual resistance was closest to

the maximum resistance in layers having low bond

strength and maximum thickness.

4. The presence of steel plates, simulating rock bolts

or other tunnel boundaries ,did not always have an

influence on the structural behavior of the layers.

In the cases where diagonal tension failures occurred,

the failure surface did not extend more than 12 in.

(30.5 cm) beyond the movable block, (curve type 1,

test Nos. S-1, S-2, S-13 and S-14). Only steel plates

located within 12 in. (30.5 cm) of the movable block

would have had any effect on the structural behavior

of the layer.

In addition, steel plates located more than 30 in.

(76.2 cm) from the movable block would not have had

any influence in the residual resistance of the layer

in test No. S-3. The minimum distance at which the

lateral restraints begin to influence the residual

resistance and displacement of the shotcrete layer

depends on the nature of the adhesive strength in the

vicinity of the movable block, the stiffness of the

shotcrete layer, and, of course, any weak zones in the

shotcrete layer created during or after shooting.

4-40

'

4.4.2 SHOTCRETE LAYER DISPLACEMENTS

Dial gages were placed against the front surface of the shotcrete

layer and attached to a frame bolted to the floor to measure the relative

forward displacements of the layer with respect to the floor. The displace

ments measured by these gages are shown in Figs. 4.29 to 4.43. These dis

placements were plotted in the same manner as those obtained in mortar tests.

The upper portion of the figure shows a top view of the fixed walls and

movable block, the shotcrete layer and the posit i ons of the dial gages on

the surface of the shotcrete. The displacements recorded by the dial gages

at each load increment are plotted in displacement profiles. The resistance

of the shotcrete layer at each increment is shown at the right side of the

displacement profile.

The displacement profiles before initial failure are very similar

for all tests in which adhesion failure occurred. Initially, equal incre

ments of load resulted in equal increments of the forward displacement of

the front surface of the shotcrete layer. The displacements were slightly

greater along the vertical center line of the shotcrete layer and decreased

toward the edges of the model. The shape of the displacement profiles, be

fore failure, was produced by the stresses imposed on the layer at the con

tact with the movable block. Since the tensile stiffness at the contact

between the shotcrete layer and the surface slabs is extremely high, the

relative displacement was almost null.

In the cases where diagonal tension failures occurred, the dis

placement of the shotcrete surface increased linearly with increasing load.

4-41

'

S-1

0 .-

50E ......... E

~ ;::1. l 00 I ......... ~ N .µ

s::: Cl) O 150 E Cl) u <O ,-0... Vl 500 .,...

-0

,-<O

~ 1000 0 s..

LL

1500

i

3 4

11 2.22 kN

(22.25kN)

e6,69 kN) 6000 1 bf to

5.59 kN) 8000 lbf

r4 Scale 2"07n.

Load

10,000 lbf (44.48 kN)

12,000 lbf (53.38 kN)

0

20

40

.-I

--..._ ______ ___.----14,000 lbf 60 _o

(62.28 kN) 00

400

600

FIGURE 4.29 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR

.--.. . s::: .,...

<::I'" I 0 ,-......... .µ s::: Cl)

E Cl)

u <O ,-0. Vl .,...

-0

,-<O .µ s::: 0 s..

LL

S-2 <t.

3 ) ( 4 ) ( 5) (6) (7 ) ( ) 1~ Sca~e , j 20 ,n.

o_ Load 0

-----50 I- J- ......... ____/ 4000 l bf j20 . s::::

(11.79 kN) .,....

/ 6000 lbf <:::I'"

E 100 I- ~ " I

..J::> (?fi_ fiq kN) 40 0 I

;:l.

..J::> ..........

w +->

O 150 [ [ ~60 +-> s:::: s:::: a,

0 a,

E ---- 8000 lbf (35.59 kN i) E a, - (lJ

u - • :~ 10,000 lbf (44.48 kN) u n::I - • n::I ,-- • I ,--c.. I • , 12,000 lbf (53.38 kN) 200 c.. Ill 50 Ill .,.... .,.... -0 -0 ,-- ,--

.:3 100 400 n::I +-> s:::: s::::

0 0 ~ ~

LL LL

600


S-3 t.

---~.•· ··

cb (j) @G) 0 00 cb 0 r Scale 20 in. • I

0 Load 0

2500 l bf

50

----E .i::, ;:l

100 I ........

t .µ c:: (l)

150 E (l) 0 u n:, r-

( 11. 12 kN) ----5000 lbf j20 . c::

(22.25 kN) •,-

7500 l bf (33.37 kN) ,;j" I

10,000 lbf (44.48 kN) 40 0 r-

12,500 lbf (55.60 kN) 15,000 lbf (66.72 kN)J

.µ c:: (l)

--------- 60 Jo E (l)

u n:,

0. r-V'l

,,- 500 -0 200 ~

•,--0

r-n:, r-.µ

§ 1000 s...

400 .;3 c:: 0

LL s... LL

1500 600


S-4

0

50 ......... E ;:l.

~ ---- 100 I .µ ~ s:::: (J1

QJ E Q.)

0 u r'd -0. (,/) .,....

500 -c -r'd .µ

§ 1000 s...

LL.

1500

i

1/4" steel plate 1/4" steel plate

6 3 4 5 J ( 6 ) ( 7 ) ( ) ~ Sea le 20 in.

Load 0

~ .. ~ 2500 lbf ( 11 . 12 kN)

1250 lbf -120 ( 5. 56 kN)

1100 lbf --I 40 ( 4. 89 kN)

60 -----.---------- 1100 lbf (4.89 kN)


• I

0

200

400

600

. s:::: .,....

o:::r I 0 ,..... ----.µ s:::: QJ

E QJ u rd ,..... 0. (,/) .,.... -c ,..... rd .µ C: 0 s...

LL.

S-5

0

50

--E ;:i

100 -+=> .._.., I

-+=> +-> O'l C Q) E

0 Q) u ~ ,-0.. (/) .,...

500 -0 ,..... ~

+-> l 000 C

0 !,..

I.J....

1500

<t.

6 3 4 5 ~ Sea~= •I 20 "'.

Load 0

1000 lbf ( 4. 45 kN)

2000 lbf (8 .89 kN)

20

40

60


0

. C .,...

'<:I'" I 0 ,..... ..........

+-> C Q)

E Q) u ~ ,..... 0..

200 -~ -0

,..... ~

400 t

600

0 !,..

I.J....

S-6 't.

1/4 11 Steel plate II I H 1/4 11 Steel plate

~) l5 J l(iAJ.IU (7 J

41

?;''~'~ 5:~e 20 l n. ~ I

o_ Load 0 5000 lbf .--..

( 22. 24 kN) . s:: .,...

5Cl- I- ~ / ✓ \ ~ 10,000 lbf 20 rj-

( 44. 48 kN) I

E

E '\__/

~ 0 ;:1.

,--..___.. -

.i::,. l 00 40 .µ I .µ s::

.i::,. s:: QJ -...J QJ

E E QJ

.1 QJ

u - 15,000 lbf (66.72 ~RJ 3 ° u

~

E - ~

,-- --.::::::: .-0. I :;:::::::- 17,500 lbf (77.84 kN) 0.

Vl I Vl .,... 200

.,... -0 -0

! lOOt ~ ~400

~ .µ s:: 0 s..

LL.

600


S-7 <t.

·••!·· ~ -~

cb 0 CD G © © © © © ~ Scale 20 in. • I

Or- Load 0 1500 lbf

( 6. 67 kN) -20 .

50r- t- -- 2000 lbf C: ,,-

(8.89 kN) tj" -E

I ~ E 3500 lbf 0 I ;::l.

100~ 40 ,--

~ .......... (15.57 kN) 00 +' +-' C: 4500 lbf C: QJ 150 QJ E 0 (20.02 kN) 60 0 E QJ QJ u u (1j (1j

,-- ,--a.

200 a.

VI 500 VI ,,- ..... "'O "'O

,- ,-(1j

400 ~ t 1000 C: 0 0 s.. s..

LL LL

1500 600


S-8

0

50 ..-... E ;:::l.

~ ---- 100 I ~

.µ I.O C

QJ E O 150 QJ u ro

,--c.. Vl .,.... 500 -0

,--ro .µ

§ 1000 s..

l.J....

1500

i

5

1/4" Steel plate

~ Seale • I 20 in.

Load 0 400 1 bf ( 1 . 78 kN) 20

1000 lbf ( 4. 45 kN)

1500 : lbf (6.67 kN) 40

1500 lbf (6.67 kN) 60 -0

200

400

600


..-... . C .,....

tj" I 0 ,--

----+> s:: QJ E QJ u ro ,.... .. c.. Vl .,....

-0 ,-ro .µ C 0 s..

l.J....

S-9 i

-~ -~--

cb 0 00 © ©0 © @ r Scale I 20 . • in.

o_ Load 0 2500 lbf ( 11. 12 kN ........

50 l _ L -------- - _____....-:: 20 . --- • •::iooo lbf C

(22. 25 kN) •,-

<d° - t ~ 7500 lbf I 3. 100 0

~ {33.37 kN 40 ,-

j O 150

......... I

10,bOO lbf (44.48 kN) ...., 01 0

12,500 lbf f 55.60 kN~ 60 o i 15,000 lbf 6!472 kN 1 "

I 5of F - l J • 12,000 l bf ~ l l 312

I (failure) 200 'c.. Ill 180 208 370 200 80 •,-

"'O

,-

400 tO +' C 0

"" u. 600


S-10 't.

1/4" Steel plate __ !: II I H ~! ,_l/4" Steel plate J,· ··· ·e d

3 ) ( 4) { 5) (6) (7 ) ( ) ~ Seale I 20 in. '

o~ Load 0 1250 lbf

(5.56 kN) . C:

50L L '---- 20 •r-

2500 lbf tj"

( 11 . 12 kN) I 0 ..........

~ ~

...-E

40 ..........

;:::l.

100~ -+=- .......... .µ I C: u, .µ Q) _.

C: E Q)

O 150 60 Q)

E 0 u Q) cu u 3800 lbf (16.9 ·kN) ,-res c.. ,-

5000 lbf (22.25 kN) Vl c..

500 200 :; Vl 6250 lbf (27.8 kN) •r--0 7000 lbf (failure ...-

res ,-

31.14 kN) .µ res 400 C: .µ 1000 0 C: s.. 0 LL s..

LL 2320 1soo 1 I .J500


S-11

0

50

,,....._ E ;:::l.

~ ---- 100 I u, .µ N i::

QJ E QJ u ~ ,-Cl. V1

•,- 50 -0

,-~ .µ i:: 0

1000 ~

LL

1500

't.

1/4" Steel plate 1/4" Steel plate

0 4 5 6 1--4 Seale • I 20 in.

I a..c::::: •c.::::::::::: :=zs •==:::: :::::>" ::.:::::;a,a hYYU t0

2000 lbf ,20

(8 .89 kN)

3000 lbf (13.34 kN) 740 4000 lbf (17 .80 kN)

5000 lbf (22.25 kN) _J6Q


~o 200

400

i:: •,-

.;j-1 0 ,-

.µ i:: OJ E OJ u ~ ,-Cl. V1

-0

~ .µ i:: 0 ~

600 LL

S-12

0

50 ,--...

E ;:l.

100 ..__.. +=> I .µ

u, s:: w (I)

150 E 0 (I)

u ro -0.. (/)

500 •,--0

,--

ro

~ 1000 0 s....

LL

1500

t.

1/4" Steel plate l /4" Steel plate

CD 4 5 I Scale ~ 20 in.

0 •

1000 1 bf -t20 (4.45 kN)

1500 l bf _J40 ( 6. 67 kN)

7 60


• I

-0

:200

. s:: •,-

""1" I 0

.µ C (I) E (I) u rd

,--0. (/)

.,--0

,--

400 ~

00

C 0 s....

LL

S-13

0

50

~ l 00 I . u, ~·

O 150

500

1000

1500

i

1/4" Steel plate

4 5

1/4" Steel plate

6

•• II II II II II

h Scale I 20 in. "

I 1liE<.....: .......__ :::::::» O a::c:::::: :::,' :, 0 ,O

~

l 000 l bf ( 4. 45 kN)

3500 lbf --420 ( 33 . 37 kN)

10,000 lbf ~40 ( 66. 68 kN)

12,500 l ~f 1 .--==--- ( 55. 6 kN r-60

( 66. 72 kN)


0

200

400

600

S-14 t.

1/4 11 Steel plate 1/4 11 Steel plate

4 5 6 I~ Scale 20 in. • I

0 Load 1250 lbf (5.56 kN) .

50 ,......_ E ;::1.

----+'lo

+' 100 c::

I OJ U'1 E U'1 OJ

u o 150 rtl -,- r-r 0 0 ·----. 0. 0 (/) .,....

"C 500

2500 lbf 20 c::

( 11. 13 kN) .,....

-=:::I" I

5000 lbf 0

( 17. 80 kN 40 ,-

----5000 lbf +'

c::

(22.25 kN 60 OJ Jo E OJ

6250 lbf (27.81 kN) u rd ,-0.

200 (/) .,.... ,-rtl "C +' c:: 0 s.. 1000 LL

,-rtl

400 +' c:: 0 s..

LL

1500 600


S-15 t

1/4 11 Steel plate ' Steel plate

4 5 6 r s ca ~ e • I 20 1 n.

Load 0 Or- 2500 1 bf

( l 1.'l2 kN ---:-

5o 5000 lbf 20 -~ E (22.24 kN <:f" ~ 0

.i::- _. 100 7500 1 bf .::. 0-, ~ ( 33. 36 kN) 4o +-> ~ W C

E w w 150 E

~ o ~ ========== . 10,000 10 60

o ~ ~ '~ : ~ (44.48 kN) ';_ :;; 500 ~---- ~ 12,500 lbf 200 .:'! .-- (55.60 kN) -o

~ ------ r-~ ' 15 , 000 1 bf ( 66 . 72 kN ) 400 ~ ~ lOOO 7000 1 bf ( 31. 13 kN) ~

LL.

1500· • .....600


In these cases the adhesive force, Fa, was greater than F1, the force

required to induce a diagonal tension failure in the shotcrete layer.

Separation of the shotcrete from the surface of the slabs occurred in two

of these tests, Nos. S-1 and S-2, but was confined to a very narrow zone,

1-1/2 to 2 in. (3.81 to 5.as cm) wide on the inside edge of the fixed wall.

The initial loss of adhesion followed by the diagonal tension failure in

dicates that forces Fa and F1 were almost equal and both the adhesive

strength and diagonal tension strength were fully mobilized.

When diagonal tension failures occurred,no additional resistance

was offered by the shotcrete layers.

The second mode of failure, separation between the shotcrete

layer and the concrete slabs, was present in all the other tests. The in

duced adhesive stress exceeded the adhesive strength between the shotcrete

and the surface slabs before the level of stress in the layer reached the

diagonal tension strength of the shotcrete. The separation of the shotcrete

layer from the surface slab started at the movable block and progressed

toward the boundaries of the layer. However, in the absence of steel plates

the length of propagation of the failure surface was at least in part re

lated to the thickness of the shotcrete. In test No. S-5, when the thickness

of the shotcrete was 5.26 in. (13.4 cm), the failure propagated to the ends

of the layer. In test No.S-3, 2.18in. (5.5 cm) thick. it progressed 15.5 in.

(39.4 cm) to a point where the bending stresses in the inside face of the

layer exceeded bending strength of the layer and a failure occurred. In test

No.S-7, carried out on a 2.78in. (7 cm) thick layer cured only 7 hours, the

adhesive failure propagated 48 in. (122 cm) on one side but only 24 in.

(61 cm) on the other where a bending failure developed.

4-57

In the other tests, the shotcrete layer, after its separation

from the surface slab, acted like a simply supported beam uniformly loaded

in its center with end supports continuously moving apart to the limits

imposed by the steel plates. Immediately after the adhesion failure pro

pagated to the plates, the bending stresses produced by the ram exceeded

the bending capacity of the layer and two vertical cracks appeared on the

outside surface of the shotcrete along the contact between the movable and

fixed blocks. The progressive separation of the shotcrete layer occurred

so fast that the cracks appeared almost simultaneously with the adhesive

failure.

In all tests, separation never occurred between the shotcrete /

layer and the surface slab covering the movable block.

4.4.3 LAYER RESISTANCE VS t'OVABLE BLOCK DISPLACEMENT

The ram load and displacement were constantly monitored using an

x-y plotter. The results were plotted in terms of unit resistance, i.e.,

the ram load divided by the vertical 48 in. (122 cm) of contact between the

shotcrete layer and the fixed walls against the 11 net 11 displacement of the

movable block.

Three basic types of curves corresponding to the three different

structural behaviors were exhibited by the shotcrete layers (Fig. 4.20).

In the load range before failure, all the curves showed a very stiff and

linear relationship between the resistance of the layer and the relative

displacement of the movable block. Once failure occurred, different struc

tural behaviors of the shotcrete layer were observed as follows.

4-58

At load levels above 70 percent of the maximum layer resistance, a non

linear relationship developed in which rate of displacement increases

faster than the rate of load.

The profile of displacements along the shotcrete layer out from

the movable block depends mainly on the tensile stiffness between the

shotcrete layer and the surface slab. It also depends on the stiffness of

the shotcrete layer and to a lesser degree on the location of the lateral

restraints. The post-failure displacements of some of the shotcrete layers

occurred very rapidly and were not measured in tests represented by type l

and 2 curves (Fig. 4.20). In tests represented by type 3 and 3A curves,

displacements of the movable block were controlled so that the displacements

of the shotcrete layer could be observed. In four of the tests (test Nos.

S-4, S-8, S-9 and S-15) the shotcrete surface displacements were closely moni

tored thus allowing the deflective shape of the shotcrete layer and the prop

agation of the adhesive failure to be observed.

The deflected shapes of the failed shotcrete layers are very simi

lar to those of the mortar layers and resemble the deflected shape of a

simply supported beam (test No. S-4 - Fig. 4.32). In addition, the dis

placement obtained from dial gages placed against the center of the block

were nearly the same as those obtained from the LVDT in the ram for the same

load increments.

4.5 EVALUATION OF VARIABLES INFLUENCING THE STRUCTURAL BEHAVIOR Of THE LAYER

Each of the 16 shotcrete layer tests was carried out to evaluate

4-59

the effect of a particular variable on the structural behavior of the

layer. The variable to be compared in a given set of tests is summarized

in Table 4.5. The influence of variables on the structural behavior will

be discussed in the following section and will be described in terms of

their effect on the observed modes of failure and the resistance and dis

placement of the movable block.

4.5. 1 LATERAL BOUNDARIES

The effect of lateral boundaries on the behavior of the shotcrete

layer can be seen by comparing test Nos. S-3, S-4, S-9 and S-10. Test Nos.

S-3 and S-9 were carried out with shotcrete layers having approximately the

same thickness and strength, however in test No. S-9 the lateral boundaries

of the layer were located 4 ft (121.9 cm) apart, while in test No. S-3 steel

plates were not used. In both tests, the same mode of failure involving

separation of the shotcrete layer from the surface slab was observed. The

maximum resistance of both shotcrete layers and the slope of the load

displacement curve were almost the same. After the peak load was reached

in test No. S-3~ the resistance dropped off rapidly after a small displace

ment (0.04 in.; 1.02 mm) of the movable block. In test No. S-9, however,

the residual resistance decreased gradually (dashed line - Fig. 4.44) and

finally reached zero after a relatively large (1.0 to 1 .5 in.; 25.4 to 38.1

mm) di splacement of the movable block. The ductility of the layer having

lateral restraint was approximately 3 times that without restraining bounda

ries.

Figure 4.45 shows the resistance - displacement relationship for

4-60

TABLE 4.5

VARIABLES COMPARED IN THE SHOTCRETE LAYER TESTS

Test no. S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-10 S-11 S-12 S-13 S-14 S-15 S-16

S-1 R S-2 T T S-3 S-4 A T S-5 T T T S-6 A S-7 M

.j:::,

S-8 M A I 0) _,

S-g L s-10 L A S-11 M

S-12 M A S-13 T T T T S-14 T T T T T S-15 Re Re Re S-16 Re Re Re

LEGEND: R = Repeatability T = Thickness value A = Adhesion surface characteristics M = Mortar strength L = Lateral boundary conditions

Re = Reinforcement


0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20 . 0 I I I I I I I I I

90 500

80 C: .... E - -'+- z .o 400 ~

S-3 70 .µ

.µ u u rtS rtS .µ .µ S-9 C: C: 0 0 0 u u

'+-'+- 0 0 300 ..c:

.j::,, ..c: 0 .µ .µ c:n

I C7l C: 0-, C: OJ N QJ ,......

0 .µ

.µ

" .... .... '

C: C: :::, ::, 200 ' s... s... ' OJ OJ ,..._ 30 c.. c.. .._ ..._ OJ QJ u u -- C: C: -- rtS rtS .µ .µ

0 VI V) .... .... 100 A

V, V) OJ QJ 0::

ei:::

10

01 I I 01 - _JO, 0 100 200 300 400 500 600 700 800




0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0

I I I I I I I I I 500

I I I I I I I

0

-. - -----C: E .,... ;;::- 400 -70 z: ..c .:,,,:

r-......... +->

+-> u u 60 "' ~ +->

+-> C:

C: 0 0 u

~ u 300 S-10 '+-

'+- 50 0 I

O'l 0 .s::. w +-> .s::. O') +-> O') C:

C: Cl)

QJ 40 ,-

r- +-> :!: 200

..... C:

C: :::,

::, s... s... 30 Cl)

(1J c.. Q. 0 Cl)

(1J u u C:

20 "' C: +-> "' 100 Vl +-> Vl

..... ..... Vl

Vl Cl)

Q) 0:: 0:: 10

0 0 0 300 400 600 700 800



~

test Nos. S-4 and S-10 in which steel plates were spaced 8 ft (243.8 cm) and

4 ft (121.9 cm) apart, respectively. No difference was observed in the mode

of failure of these 2 layers. The difference in the maximum resistance of

the layers was probably caused by a greater adhesive strength along the con

tact between the layer and the surface slab in test No. S-10. The greatest

difference in the structural behavior of the two layers can be seen in their

residual resistances. Where the steeJ plates were spaced 8 ft apart (test

No. S-4), the residual resistance. of the layer did not exceed 50 lbs/in.

(8.8 kN/m) and was reduced to zero for a displacement of 0.2 in. (5.1 mm).

On the other hand, where the steel plates were located 4 ft apart (test No.

S-10), the residual resistance of the layer reached 200 lbs/in. (35 kN/m) ,

at 0.02 in. (0.51 mm) displacement and decreased to zero only after the

movable block had displaced an additional 0.8 in. (20 mm). The difference

in the residual resistance of the two layers was not only caused by the

location of the end restraints but also was related to the greater thickness

(1 in.) of the shotcrete layer in test No. S-10.

From the results of these tests, the following conclusions with

respect to the structural behavior of the shotcrete layers were drawn:

1. The initial mode of failure and the maximum resistance

of the shotcrete layers were not affected by the presence

of steel plates within l ft (30 cm) of the movable block.

2. Observed variations in the maximum resistance of some

layers were caused by differences in adhesive strength

and not by the differences in the location of the lateral

restraints of the layers.

4-64

3. Both the load carrying capacity and the displacement

of the layer after adhesion failure were affected by

the position of the steel plates.


Variations in the mode of failure and in the maximum and residual

resistances of the layers were produced by differences in shotcrete thick

ness. For shotcrete layers having thicknesses ranging between l. l in. and

1.9 in. (26.9 mm to 47.2 mm) and good shotcrete-slab bonds, diagonal tension

failures occurred in the shotcrete layers (Fig. 4.46). The maximum resistance

of the layer was directly related to the thickness of the shotcrete. In all

of these tests the residual resistance of the layers rapidly decreased to

zero.

The mode of failure changed primarily to separation of the shot

crete layer from the surface slab when the thickness of the shotcrete reached

approximately 2.2 in. (5.53 cm) as seen in test No. S-3. The maximum resist

ance offered by the layer increased slightly as well as the displacements of

the movable block relative to the tests in which diagonal tension failure

occurred. Further increases in thickness, at least up .to 5.26 in. (13.4 cm),

did not affect the overall mode of failure nor the maximum resistance of the

shotcrete layer.

For test Nos. S-4 and S-6, in which filament tape was used to reduce

shotcrete-slab bonds, the shotcrete thickness had no effect on the failure

mode or the maximum resistance of the layer. This would be expected since a

diagonal failure could not develop in layers having loose bond unless restraints

were placed close to the movable block.

4-65


0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 5.0

I I I 0

500

80 -. C: -.,....

........ 4--.0

e ........ 70 z

~

--- ,--- -+-'

+-' u u

rd rd +-' C:

60 +-' C: 0

0 u u

4--0 ..,.

4--0

50 ..c: I ..c:

O"I +-' O'I C'l

+-' C'l C:

C: QJ (l) ,--

,--

+-' .,.... 40 +-' I I ....

C: S-13

C: ::::, ::::,

s... (l)

s... 30 QJ

0. 0.

...... (l) QJ u

u C: C: rd +-'

rd 20 +-'

VI VI .... .,.... VI VI (l)

0:::

QJ

~ 10

20 40 60 80 100 120 140 60 0


FIGURE 4.46 UNIT LENGTH RESISTANCE ·vs MOVABLE BLOCK DISPLACEMENTS

In tests where the shotcrete-slab bond was low and the thickness

of the layer was high (test No. S-10) the maximum resistance of the layer

was controlled by the bending capacity of the layer rather than by the ad

hesive strength. As the thickness increases ,the bending stiffness of the

layer increases and thus provides an increase in bending strength. In test

No. S-10 the bending capacity was governed by both the thickness (3.1 in.)

and the spacing of the steel plates (4 ft).

The following conclusions were drawn regarding the influence of

the layer thickness in the structural behavior:

l. For a good shotcrete-slab bond (roughened surface and

7-day curing), the primary mode of failure changes from

diagonal tension to adhesion as the thickness of the layer

increases above 2 in. (5.1 cm). Once this thickness is

reached, further increases do not alter the mode of failure.

2. For diagonal shear failures, the maximum resistance of the

layer is directly proportional to layer thickness. For

adhesive failure the thickness does not affect the maxi

mum resistance unless the shotcrete-slab bond is poor

and the layer has a greater bending capacity than adhesive

strength. Where diagonal failure occurred the maximum re

sistance ranged from 150 lbs/in. (26 kN/m) for a 1-in. (2.5 cm)

thick layer to 320 lbs/in. (56 kN/m) for a 2-in. (5.1 cm) layer .

3. The residual resistance of the shotcrete layer increased

with increasing shotcrete thickness. A residual resis

tance of 30 lbs/in. (5 kN/m) was observed in test No. S-8

4-67

l

having a thickness of 3.0 in. (7 .5 cm), while in test

No. S-6 the resistance of the 4.7 in. (11.9 cm) layer

was 50 lbs/in~

4.5.3 ADHESIVE SURFACE CHARACTERISTICS

Changes in the structural behavior of the layer resulting from

differences in shotcrete-slab adhesion can be seen by comparing pairs of

test Nos. S-3 & S-4, S-5 & S-6, and S-9 & S-10 performed at 7 days. The

differences in adhesive strength for each pair of tests was obtained by

using a roughened surface (representing good bond) and a surface covered

with tape (poor bond). The same mode of failure, separation of the shot

crete layer from the surface slab, was observed in all the tests; however,

the maximum resistance was strongly influenced by the adhesive strength

developed between the shotcrete and the slab. The maximum resistance of

layers having poor shotcrete-slab bond were approximately 20 percent of

those in which the shotcrete was placed against roughened contacts (Figs.

4.22, 4.23 and 4.25). The higher resistance obtained in test No. S-10

relative to tests S-4 and S-6 was caused by localized penetration of shot

crete in the slots surrounding the movable block. Although maximum re

sistance was strongly affected, the residual resistance was not sensitive

to surface adhesion when lateral restraints were present.

Similar results were obtained for the 7 hr tests (test Nos. S-7 &

S-8 and S-11 & S-12). However, the maximum resistances of the layers having

poor bond was 30 to 40 percent of the values obtained for the wire brushed

surfaces. The residual resistance of the 7 hr tests were the same for

4-68

both taped and untaped surfaces where the restraints were placed at the

same location. Based on the test results, the influence of surface ad

hesion on the structural behavior of the shotcrete layers are summarized

below:

1. For shotcrete layers greater than 2 in. (5 cm), the

failure mode is not changed by bonding conditions of

the surface. However, diagonal tension failures can

develop when shotcrete thickness is less than 2 in .

(5 cm) and shotcrete-slab bond is good. These failures

cannot develop when bond is poor, independent of the

thickness of the layer.

2. Poor contact bond can reduce the support capacity of the

layer as much as 60-80% relative to layers having good

shotcrete-slab bond. The greater reductions occurred

in shotcrete layers having higher strengths (7 days).

3. The residual resistance of the layer was the same for

both good and poor shotcrete bond strengths when lateral

restraints were present at the same locations relative

to the movable block.

SHOTCRETE STRENGTH

The variations in the adhesive strength caused by differences in the

time of curing were studied by comparing results of test Nos. S-3 & S-7, S-5 &

S-11 ,S-4 & S-8,S-6 & S-12. The strength of the shotcrete layers does not affect

the mode of failure (separation of the shotcrete layers from the surface slabs),but

4-69

bond. It had the greatest effect on the roughened

surfaces while the taped surfaces were not as sensi

tive because the smoothness and impermeability of

the tape tended to control the adhesive strength.

When the bond is good ,shotcrete 7 hours old has

approximately 1/5 the support capacity of a comparable

7-day old layer. However, with poor bond only a slight

increase in the capacity of the layer occurs (30-50 lbs/

in.) between 7 hours and 7 days.

3. The residual resistance of the layer is directly pro

portional to the curing time. For the 7 hr test, the

residual resistance of the layer was 1/4-1/5 of the

value at 7 days.

4.5.4 USE OF REINFORCEMENT

The influence of steel fiber reinforcing in the shotcrete layers

can be seen by comparing test Nos. S-4 and S-16. The layers in these tests

are very similar except that in test No. S-16, steel fibers, 0.01 in. x

0.022 in. x l in. (0.025 cm x 0.056 cm x 2.54 cm), were added to the shotcrete

before gunning. The presence of fiber produces no significant increases in

the maximum resistance of the shotcrete layer (Fig. 4.48). However, both the

residual resistance and ductility were greatly increased when fiber was pre

sent in the layer.

Residual resistance of the reinforced and nonreinforced shotcrete

layers placed on roughened concrete cannot be compareddue to different lateral

4-72

500

. s:: •,--...... 4-.0 400 ,--

----.µ u .,, +-' s:: 0 u

4- 300 0 .i::,. I .c

........ +-' w Ol

s:: (1,)

,--

.µ •r-s:: 200 ::I

s... (1,) a. (1,) u s:: .,, +-' (/) 100 •r-(/)

(1,) 0::::

0


0.25 0.50 0.75 1.00

S-16

300 400

Movable block displacements FIGURE 4.48 UNIT LENGTH RESISTANCE VS MOVABLE

1.25 1.50

500 600 ( -3 10 in.) BLOCK DISPLACEMENTS

l. 75 2·~00 ., 90

80 ,-... E -...... :z

70 .=.. +-' u .,, +-'

60 s:: 0 u 4-0

50 ..s:: +-' Ol s:: (1,)

,--

40 +-' •r-s:: ::I

s... 30

(1,) a. (1,) u s:: .,, +-'

0 (/)

•r-(/)

(1,) 0::::

10

JOO 800 0

boundary conditions of the layers. However, differences in the adhesion

surface conditions do not alter the residual resistance characteristics

of the layer. From the above mentioned results it can be concluded that:

1. The use of fiber-reinforced shotcrete does not

change the mode of failure nor increase the maxi

mum resistance of the layer as compared with con

ventional shotcrete under similar conditions.

2. After adhesion fail~res occurred, the steel fibers

increased the ductility of the layer and provided

greater post-crack resistance.

4.5.5 REPEATABILITY 'OF THE TEST RESULTS

The repeatability of the test results was checked by performing

two tests having essentially the same conditions (test Nos. S-1 and S-2). Even

though a relatively small difference existed in the thickness of the layers,

±0. 1 in. (±.25 cm), the same structural behavior was observed and the maxi

mum resistance of the layers was very similar. In both cases the residual

resistance decreased rapidly to zero after the adhesion failure. It can be

concluded then, that the shooting and testing conditions can be controlled

accurately enough to reliably reproduce test results.

4-74

CHAPTER 5

SUMMARY AND CONCLUSIONS

5. 1 MAXIMUM RESISTANCE OF THE LAYER

In the tests where failure primarily involved separation of the

shotcrete layer from the slab (adhesion failure), the maximum resistance

was directly proportional to the adhesive strength along the shotcrete-

slab contact and was almost independent of shotcrete thickness. The dashed

band in Fig. 5.1 shows the linear relationship between the maximum layer

resistance and its adhesive strength. In these cases the maximum resistance

was equal to F0, the resultant force of the adhesive strength developed be

tween the shotcrete and the surface slabs. The relatively high resistance of

the layer in test No. 9 was caused by the presence of shotcrete in the slots

surrounding the movable block.

In the tests in which diagonal tension failures occurred, the

maximum resistance was directly proportional to the thickness of the layer

and to the shotcrete strength. The measured resistances coincided very

closely with calculated values of F1 , which is the shear force required to

induce a diagonal tension failure in the layer. Values of F1 were calcu

lated assuming the diagonal tension strength of the shotcrete equal to

2/f'c (where f'c is the compressive strength of the shotcrete) and are shown

by the horizontal dashed lines in Fig. 5.1. In tests involving adhesion

failures, the calculated values of F1 were always greater than the actual

maximum resistance of the layers. On the other hand, the calculated shear

forces (F1) were always less than or equal to the maximum resistance of layers

5-1

Adhesive strength (KPa) 0 200 400 600 800 1000 1200 1400

160 I I I I I I I I

35 ----------,..----------------

140 --------------- @

30

® 120

25 ----------------------- ®

100

20 e9 @

,,....._ z: Vl

.:=. 80 0.. •,-~

X l'tl E X

0... l'tl

0... E 15

60

10 40

20 5

0 40 80 120 160 200

Adhesive strength (psi)

FIGURE 5. l MAXIMUM RAM LOAD VS MEASURED ADHESIVE STRENGTH

5-2

in which diagonal tension failures occurred. In these cases the values of

F0 given by the dashed band were much greater than the actual maximum re

sistance offered by the layer.

The structural behavior of the layers depends on the mode of fail

ure which is controlled primarily by thickness and bond of the shotcrete.

For any given layer when the diagonal tension strength is greater than the

adhesive strength,a separation of the shotcrete layer occurs and the maximum

resistance offered by that layer is given by the force F0. On the other

hand, when the diagonal tension strength is less than the adhesive strength,

a diagonal tensile failure occurs and the maximum resistance offered by the

layer is given by the value of F1. This structural behavior corresponds

exactly to the one proposed in the model of Chapter 3.

5.2 RESIDUAL RESISTANCE

Visual observations together with the displacement measurements

indicate that the shotcrete layers behave as simply supported beams uni

formly loaded in their center sections after an adhesive failure develops.

The load carried by each shotcrete layer acting as a simply sup

ported beam (Fig. 5.2) was calculated using the geometric characteristics

of the layers, shotcrete strength and distance between the lateral restraints

and the movable block. The values of the layer properties used in the cal

culations as well as the calculated and measured residual loads of each

layer are summarized in Table 5.1.

Except for test Nos. 9 and 10, the measured and calculated resid

ual loads assuming a simply supported beam are very similar although the

5-3

• uunm w ~

L _, L

a) SIMPLY SUPPORTED BEAM

~ UIUUU ~ ~ I~ _, L

b) DOUBLE CANTILEVERED BEAM

FIGURE 5.2 BEAM MODELS USED IN RESIDUAL CAPACITY CALCULATIONS

5-4

measured value is usually slightly higher than the calculated value. The

difference between the calculated and measured residual resistance values

was probably provided by the steel plates which served as a restraint against

rotation at the extremes. It must be pointed out that the residual resist

ance values measured were much closer to the lower limit obtained assuming

a simply supported beam than the upper limit calculated assuming develop

ment of a double cantilever beam (Fig. 5.2 (b); Table 5. 1). Calculated re

sidual resistance values assuming cantilever action at the beam supports

were 5 to 10 times higher than the actual values of residual resistance.

The double cantilever beam did not develop because of the flexibility of

the steel plates and their supports. The closer the restraints were to the

movable block,the more the layer tended to act as a cantilever beam. For

test Nos. 9 and 10 in which the steel plates were located 1 ft (30.4 cm)

from the movable block, the measured values of the residual load were 4

times higher than the value estimated for a simply supported beam. After

large displacements (1 in.; 2.54 cm) of the movable blocks, the load de

creased to 2200 lbs (9.79 kN); this was only twice the calculated value.

5.3 GENERAL CONCLUSIONS

Results of the tests carried out on the mortar and shotcrete

layers confirm the validity of the model of behavior of thin linings on flat

tunnel surfaces given in Section 3.3.

l. Two modes of failure were considered in the model: separa

tion of the shotcrete layer from the surface slab and

diagonal tension failure in the shotcrete layer. Both

5-5

2.

modes were observed in the testing program; their

occurrence depended on the relative value of forces Fa

and Fl .

The max i mum resistance offered by the layer depends on

t he mode of failure and its magnitude is given by the

smaller of the forces F0 and F1. When separation of

the shotcrete layer occurs, the maximum resistance is

directly proportional to the maximum adhesive strength

per unit area of contact. For variations in the adhe

sive strength from 180 psi (1241 .l kPa) to 20 psi

(137.90 kPa), maximum resistance per unit length of the

movable block contact ranged from 400 lbs/in. (70.05

kN/m) to 50 lbs/in . (8.76 kN/m).

If a triangular distribution of the adhesive strength

between the shotcr ete layer and the surface slab is

assumed, the distribution of stress does not extend be

yond a few inches ( 2 to 4 in.; 5 to 10 cm) away from

the movable block. The load applied through the movable

block is transmitted by the shotcrete layers along two

narrow (2 to 4 in.; 5 to 10 cm - wide) bands parallel to

the contact between the movable and the fixed walls.

Test results indicate that variations in the surface ad

hesive conditions (wire brushed or taped surfaces), or

in layer properties (thickness, strength) does not sig

nificantly change the width of these bands. Theoretical

5-6

considerations, i.e., beam on elastic foundation theory,

would predict that the area over which adhesive strength

is distributed would remain constant since the stiffness

in bond is much greater than the flexural stiffness of

the beam.

3. The capacity of the shotcrete layer in diagonal tension

depends on the thickness of the layer and in shotcrete

strength while in adhesion it is governed by the surface

characteristics and shotcrete strength (as affected by

curing time).

4. After reaching its maximum resistance,the structural

behavior of a conventional shotcrete layer depends

mainly on the mode of failure, the adhesive surface

conditions, the lateral boundaries of the layer, and

the strength and stiffness of the shotcrete. When

separation of the shotcrete starts, the adhesive fail

ure propagates away from the movable block depending

on the thickness of the layer and the slab surface

characteristics. The length of propagation of an ad

hesive failure for wire-brushed surfaces varied from

48 in. (120 cm) for a 5.26 in. (13.5 cm) layer to 15.5

in. (39 cm) for a 2.18 in. (5.54 cm) - thick layer.

When the adhesive strength is low, the failure propa

gated all the way out to the boundaries of the layer

independent of layer thickness.

5-7

When steel plates were present, the adhesive

failure was terminated at the plates and the shot

crete layer acted as a simply supported beam. The

residual capacity of the layer varied with the spacing

between plates and the thickness and strength of the

shotcrete. When plates were located 4 ft (122 cm)

apart the residual resistance of the layer was 110 lbs/

in. (10.5 kN/m) while an 8 ft (244 cm) spacing pro

duced a residual resistance in similar shotcrete layers

of 60 lbs/in. (5.7 kN/m). The flexural strength and

thickness both govern the load carrying capacity of a ,,

beam. In tests where the restraints were spaced 8 ft

apart, an eight-fold change in strength produced a

two-fold change in the residual resistance of the

layers (60 lbs/in. to 30 lbs/in., respectively). The

residual capacity of the layer varied with the spacing

between the steel plates. When the plates were located

4 ft (120 cm) apart the residual resistance of the layer

was 110 lbs/in. (19.3 kN/m) while an 8-ft spacing pro

vided a residual resistance of 60 lbs/in. (12.5 kN/m).

5. No residual resistance was observed in shotcrete layers

that failed initially in diagonal tension. Fiber rein

forcement increases both the residual resistance and

ductility of a shotcrete layer. The residual resistance

of fiber-reinforced shotcrete remained constant for

5-8

displacements of the movable block of up to O,ff in.

(2 cm). These displacements were approximately 5 times

greater than the residual displacements of similar

non-reinforced layers. A rate of loading does not

appear to have a significant effect on the maximum

resistance of the layers. For changes of 2 lbs/sec

to 5000 lbs/sec the layers showed a variation ±5 lbs/

in. which is less than the variation between similar

tests run at the same rate of loading.

RECOMMENDATIONS

1. The range of adhesion tested in this program is believed

to be fairly representative of the range of values en

countered in the field (Cecil, 1970 and Bortz and Singh,

1973). Values of the adhesive strength between shotcrete

layers and typical rock surfaces from different rock types

should be investigated to aid in predicting shotcrete-rock

bonding conditions in the field.

2. Considerable differences in modes of failure and shotcrete

resistances are expected for geometries other than a

planar configuration of movable blocks and adjacent blocks.

Such tests are to be carried out as a second stage of this

investigation.

3. The support capability of fast-setting (reg-set) cement

should be investigated.

5-9

4. A numerical model simulating the structural behavior of

the layers should be used to conduct a parametric study

of the main variables which affect layer resistance.

The results obtained from the mortar and shotcrete tests

would first be used to verify the numerical model. Once

the model is verified, it can be used to establish the

effect of the main variables having values different from

those used in the tests on the resistance of thin shot

crete layers. Such a modeling could be done using a finite

element technique where viability has already been sub

stantiated (Jones, 1975).

5-10

REFERENCES

Cecil, S. 0., 11 Correlations of Rock Bolt-Shotcrete Support and Rock Quality Parameters in Scandi navian Tunnels, 11 Ph.D. Thesis, University of Illinois, Urbana, Illino is (1970).

Cording, E. J., "Measurement of Displacements in Tunnels, 11 Proceedings, Second International Congress of the International Association of Engineering Geology, 2 :VII-PC-3. l - VII-PC-3.15, Sao Paulo, Brazil (1974).

Cording, E. J. and Mahar, J. W., 11 The Effect of Natural Geologic Discontinuities on Behavior of Rock in Tunnels," Proceedings, Rapid Excavation and Tunneling Conference, San Francisco, Vol. l, pp. l 07 -138 ( 197 4) .

Cording, E. J., "Geologic Considerations in Shotcrete Design, 11 Use of Shotcrete for Undergroudn Structural Support, ASCE and ACI SP-45, pp. 175-199 (1974).

Craig, L. Curtis and Brockman, L. R., 11 Survey of Tunnel Portal Construction at U.S. Army Corps of Engineers Projects, 11 Symposium on Underground Rock Cha mbers, Phoenix, pp. 184-185 (1971).

Jones, R. A. and Mahar, J. vJ., "In strumentation to Monitor Behavior of Shotcrete Support Systems, 11 Use of Shotcrete for Underground Structural Support, ASCE and AC! SP-45, pp. 297-319 (1974).

Parker, H. W., 11 Current Field Research Program on Shotcrete, 11 Use of Shotcrete for Underground Structural Support, ASCE and ACI SP-45, pp. 330-350 (1974).

Peck, R. B., Hendron, A. J . and Mohraz, B., 11 State of the Art of SoftGround Tunneling, 11 Proceedings, North American Rapid Excavation and Tunneling Conference, AIME, l :259-286.

R-1

APPENDIX A

This appendix contains a plate in which the principal character

istics and dimensions of the different load-applying rams components are

shown. Various cross-sectional areas along and across the ram axis, ac

companied with explanatory descriptions, are also shown in this plate.

A-1

);:, I

N

APPENDIX A

i> r(eJ Y 0,A lttl0VNTINd, N0L~5 ' c~v.,,, $PA(CO OH A

w o,A ao,, Cll'fCL•

r C/IVll"O"'MLY T(j,QUC AL4.CN NUT, TO T ~T. ,.,. -J ;,;,:~z,_~,~~~<,£j uou~

!'{. •< c ,o :'_'fl"d"''g ~ ~· •·.,. ,J ... , , · c· -:-::-• .. ·•• · .... . ·•- ~· - · ; •· .. ·a•· .. •.~,· .... . n I ~, ~ n~£:~~}F...--- r:~'.;.~ - -• -~~~; ~~-~:r:tt~;'~~~~J~!;_;j;,;Sm-3-:f; _ -~3i~-~'~

-~.,,O';f;.""!~v;,~':t!ti•~°!,~/ / ~Ao~~-;"c,u;_~~6 HOlO 1 ~C:~,":'t;';';;~~ ,,oL,1 rPT,;U••10••I"'

Ar '""' TOA '''"''-'- II~ I """"'°c" ~0--•1 ; · Moor, r o• .•.r. _I PICl.,W•IO· •.S.

0 ; 11 ' '.ADJ Cl'TI(),.,, . ~

,. • ._,._.,,.~£' (N ~u. ,v;oor,1/ j IP J I ;:,A $~NhC.• ;,,..g :;;~i,~~ · t//lR£/',l'(.'4 HOLC$(4) .°l> ~

- (4) If C11t MOUNrtN• "'()L~I , I £(jl.JAtLr !PlftCC.0 ON A I w C,1A 1uxr c,1tc1.c

-' ,,,,,oc,C&, ZO•. f,t ~"'O Z04.4l

IZ> ,~~'~1

IP 1Z> r· ·• I ~ .$rANOAWO r·- ·3'No,<C· ·-·7

·12> ' ·sa· l1'CT,VC~~ ;., -or~,.o~--o. · IJ>lt>

,o~.:.cw~1.. r.o .0.3 .5NO"""w / U,,,,LC,, Q1"1,,Ll/lf/¥l 3~ ""f.Q 'O.

rwj -. T [email protected] l 0~~

00-l . . . -1-" ··. . . . " 0 . "

[_ __ l _lJ 00 , if'. _j ,"~o0 ;::J f( .SH",~Al.. !>t.,IT

} :, S l"CN T.5 ,llrNIJ ."° "'C £ 1 <.1 r,o 1'10N

I I ..2,',{ i ~,.. UY ·-:.-<J>-4. J_ /. _J I 1.z• -- ~ ;... _ ._ :,; ' ·'• • ..J-c_ -- J 0 l vor Ol:. P, AC£1.1~Nr

-- If ---' ~ I( ~ ~" - 'o~A;:l;iu£,~ :sc~CltllAT,C

~

•OT(<T,W! ••HD<t: 0 .!,WIV€°t. l-4€AOA~3J' ! - C,-,,o.n,,i;~ A 1',t0 AIV'4NIF"0..0 A3$Y'

I :cc:.~~ (.Ot)N T 1H r·oo·l S.,, -r,: <,P.., MCOO ~Elll •C~ : HONN r,:1 I#<;::, ft'

ED--~~i - :--• · , '"' / 0"•"···~ ... , ,;a;,,.!~ I I -L~

1 -□- e , • , I Q P (;) - qp: - --~ ~ -=• -· - Q--j · ? I ~

J I ;z_J==~ I 1 - G - - G •

~o~I -{Lu· 0// /,, aoe ,.,.,..,,,.. A,-c \ u -~ l.... l~-o _:

' , Pt TU #ooN co,.,, ,ccr,o,,, 'OIi' tl:>- I

p --·cc·-; ... ~Li-c,, VP ,o IS~ ,... _ __ N--------. _ ,. _ 0 L°"'O CCLL li ,>ROf<c TM< ~-o«

- . , ,, ,./IC ~Re; ::,5 ;..1#£ ANO l(CTIJA/'11 i- c , """"[C T,C..N ro,r "'AL l"l.!> 0 .,C/lf I~ ~ ..

$P,,.,.,. WCO<,I!: (Z) I ~,,,..,,,A,v, 4NO __ ,rc.o .,,.,.

~ ,·'\·'\ ','\, ' . · ·· · ·-····- ·- '- .~ '- "-'>',\'~· I

! /; / ~.,,;b;) '::-; ;nee-: -~"'---I F /ij/~ I

-· --- • .ll5 '- 0P'ION4L $11//llL IJ::>0 ,. ----IP-

(Z::::-, sr~ .. CJ:. ,.O',!~c>;,rc LC,.,,.,,,., I~,.-: 0 TH L '1t L. C ,16r,,. ~T.~QJlf£3 A//fC OPTIONl4L. :w,,... , A.,t !J /\1 ~1CN44. .3';"N01" ~ 1.3 L•.

{t>, T ... t,. c c , MEN~1.:.1o1s ... ,,,,E 8A3~0 ON ,,ccr:,ATO R , Jill,nN6 I' - ~11110Jlf£ , .i.oo 1.00· TO TUC;:,(!;. .=, . ,-.-c.,,._" ,0,.,,3 ,.C//f , ,n,c H ,oo- ,,.,CAC~~ e. "" .$T.#TG ,.t: . ~ ~ IJ , _.A(.T oo · FO,. t:A(. "" , .oo· 0C(.lf£A~15 , ,., $TROKE.

Q::> , ... c zc. • ,Ac,1v4 r o R ,..,,4 , Y L. .'.:>N6 cu::, ... ,~,.,,,~ c,,-., l!AC M ' CHO . • ? , MCNSI0N~ illlfC .C, I VCN !"'OJI' NOMINAL .,:.· c//f,tlTlff(, .:1 ..... :J JlfC A NO 00 l'ltOT IN(:.L.<.10< 'T CV!H , f';"rl>. i Ort'~ L :::,r111,r,c ~r•o,r,: / $ C QVl44 TO THI: ,,. J ,,,,,. ,1.,;. L ~r .rc ,.~ Pi...J.3 z c,J.

::t::> ;i;.•r .,4, r,1,1 0-,, £ ~,o c GT A<. Tv4TCR I~ ,3TAN0A,.,0. c ,rl'tA POlfT:3 1411£ CPTtONAL Q,llt "4:S Rt:Qu11te.o er A CCC$, O R 1£:J, . [t> (7\ ~ •IAA 1110 0 /,,£,v t',TH -o II~ AOC'lD TO UIM . C RNO 0111,II 0 . •

...:=:-- ';;.toe, _ , ,-o • .,, ~HO ~(}4 . IJ t4nO ~ C,. , C.3 404, . ~lf. A.,-11:. , ~1.111..c ;,n ,.., P t:J; TON ~ CAL . :.,,",llfN0AR0 ON ~C~t€3 20• . .111 r.,.,o re • .•• · t

~ ,= .. - ~! 1',() T , .-. c .. . •: c .n .. ~ .... ON ~!ll"l ~ ~f ~ -~.'."C CrJ.3HI0N . .< 'C,, A ,.,. .. ,., ,.,,U #tA 1400 N A,-,0 T . F O/;f A,A, N • IIAU M ;:,v:,,,.-,,c, -, F;IOltll 'B8:

0 , ."',/OIC ATC3 , T~M3 T,-,A , ,.,.(! oP7IC,N AL ,.;vo M u~ r BC ,1DEC,F"ll.0 AT r, MC OF 0/lfOCR.

e:>, cce:, lttOT ,,.. ✓: ,. I.JOE P1.JrON /l,~Y""4 c T~O / HJ'O CV3HtON F"C,/f MA .. / ltJV/lfll AOD O ANO r. /"'C, /lf N llhN U M ,;v~Tl"ACr y Fl-fOM C .

(!:>- ,-.=o c, . ..,,,,c~•Ol'I . E. . r::, C . rc e AC :-.... ,, , TCD l CN.1'/'I • POD o,r.11:,. ,10/11 · £ · To ·o· F°"' c.rreNOE.0 LCNC,,TH.

.P I 4 I R

- ,SCl'IAP~P R 1N(j, /lt£TA,,,.f Clf

• 'J-CU,, .:,~AL

5l£ NOTE: ~ ~ ~ I\'> AL.,0 .

0 I ZS ,o 4-0 <,P/tlll M00O -= ~ lf •l.:S :.-o-• .,,, I -_:y ~) / ◄ JIC l.),R,a ,N CC,.,N/!CTION

~ UB:f ~ ,vor CON•,,cro,o, e£NO,. • - TJ'PC P r r., ,lA 10 f,,,P N IT,.,

L_ 11 MATIN(, P 'i"O•W·10- ♦ .S -- -- · 0 _r..== ::::tn; __ _ _ r '.,OT ,_,OU,1NO, A.3.) ,'

~.:r-- 0

1-- c,..;--,. w J

I :_ l.,- r1"',...,.,.,.; iz> -

LU~~i . L r,C!;J1T10N'4C 3Elfll01t'AL.V~ ANO A,,l,AN/,CX.0 ....,, ...

r,11:, Ow,. 1: ~.c. !!'C ,,oy--, ,, r •>. ' 11V . r,· ·.• ,::

f:~:.~::·1:;~L~18;~::~~;,·~::::~ ~: -~~~.=,t~~~~ :.~~~ MOOE:l ;<04 ,<-CTU'-TOR: ... . -- ·· -.-

,~- ___ ,:.,~5 ·r A1~c:_-~1.tc·n~ 1G11::_i,~ -D-?9..5c~

~ , ~$•1~•! r 0'11'(No, 4 IOOol • • •••~••• •- .. ,, , .- t •.• ,. I _ I

APPENDIX B

The roughness of the concrete slabs was measured to compare the

different surfaces used in the mortar and shotcrete tests and for future

comparison with the roughness of actual rock surfaces.

A cold rolled steel surface was used as a standard to compare

different slab surface conditions.

Surface roughness was measured with a device designed to measure

the vertical relief along the surface of the slab minimizing damage to the

irregularities and thereby reducing chances for erroneous results (Fig. B-1).

This device consists of a base, a rotating arm and a contact needle. The

base of the instrument rests on three legs placed on the surface of the

sample. The length of each leg is adjustable so that the base can be lev

eled. The base support remains stationary while the arm, which contains

the sensing element, rotates about the centoidal axis.

The rotating arm is attached to the base on one end and holds the

contact needle on the other. The contact needle is located 10-1/2 in. (26.7

cm) from the axis of rotation. When measuring the roughness of a sample,

the arm is rotated slowly and the needle is maintained in continuous contact

with the surface. The needle is vertically displaced by the undulations on

the surface of the sample. This vertical displacement causes a corresponding

deformation in the cantilever arm. A strain gage mounted on the arm measures

the strain induced on its top caused by the deflection of the needle. A

linear relation exists between the deflection and the recorded strain.

The results of the roughness measurements are plotted directly on

B-1

FIGURE B-1 ROUGHNESS MEASURING DEVICE

an x-y chart recorder. The instrument is calibrated and appropriate scale

factors obtained so that the actual rotational and vertical displacements

can be determined. The horizontal scale factor isl in. equals 2.2 in. of

arc distance and the vertical factor isl in. equals 0.0125 in. of vertical

displacement.

Measured surface roughness of the cold rolled steel and typical

rough and smooth slabs are shown in Figs . B-2, B-3 and B-4, respectively.

Two main characteristics of the slab roughness were detected: 1) pits and

2) bumps. Pits are crevasses on the surface which have extremely small

widths but are very deep. Bumps are surface discontinuities which have

widths of considerable extent in comparison with pi ts. They usually have

second order features on the roughness plots.

B-2

Distance along 180° arc (cm)

0 10 20 30 40 50 60 70 80 90

125

3.0

1001 ' l ,2.5

- ...--..

s:: .... 2.0 E (Y) E I -0 75 r- VI - VI co Q)

I VI s:: w VI ..c QJ O') s::

1.5 :, ..c 0 O') ~ :,

0 O'.'. 50

I I I 1.0

25 0.5

0h 4 ~ 1~ 11l5 2

10 ~4 2

18 ~2 • 0

Distance along 180° arc (in.) FIGURE B-2 Test l (11/4/74) Cold rolled steel (very smooth)

Distance along 180° arc (cm)

0 10 20 30 40 50 60 70 80 90

125

3.0

100 I I } I \ ft.A.... I 72.5 -.

C: .... M r ( 2.01 I

~ 75 --------c::o Vl I +'> Vl

~ Vl

VI Q) Cl) C: C: 1.5 -§i .r:::. OI ::::, ::::, 0 0 ex:

o::: 50

- I .l \ I I J,.o 25

0.5

0 ~o---~4----s"-----, .... 2----,6~---2.L.o----24'-----.1.28 ____ 3.1..2 __ ___, 0

Distance along 180° arc (in.) FIGURE B-3 Test 1 (11/12/74) Mid-north finjshed side

- Distance along 180° arc (cm) 0 10 20 30 40 50 60 70 80 90

125

3.0

,oo I I 72.5

--· ....... . C: .,....

2.0 ----E M E .........

I 0 75 ,.....

co ......... V1 I V1

01 V1 Cl)

C ..c:

V1

1.5 Ol Cl)

:::, C:

..c: 0

0::: O'>

~A.ti-:::, - -0 50 0::

I I ~ I I 1.0

I I '- I I -25

I I ~-. I I .5

0 ~ t ~ k , ~ 116 2b 24 2~ J:5 '

0

Distance along 180° arc (in.) FIGURE B-4 Test 3 (11/11/74) South top form side

-

APPENDIX C

Tensile tests to measure the adhesive strength between the shot

crete and the surface slabs were carried out on samples cut from the model.

The size of the samples and the sampling method have already been described

in Section 4.3.3

EQUIPMENT USED IN THE TENSILE TESTS

The equipment used to perform the tensile tests is shown in Fig.

C-1. The sample was attached to the MTS loading machine shown in the center

of the picture. The tensile load was applied at a uniform rate and was elec

tronically controlled using the console shown on the right side of the loading

machine. Deformations were measured across the shotcrete-slab contact using

MTS strain gages. The loads and corresponding displacements were continuously

monitored on a chart recorder.

Figure C-2 shows a close-up of the sample in the loading position.

Each side of the sample was connected to the loading machine by means of

steel plates and a clamp which was welded to a double joint firmly held in the

loading head of the machine. Each clamp was provided with a set of screws

that exerted pressure on the steel plates in contact with the sample. This

arrangement plus careful sample preparation produced a relatively uniform

load with no noticeable eccentricity and did not allow slippage along the

grippers. The strain gage used to measure axial deformation was placed so

that its reference points, located 1/2 in. (1.25 cm) apart, bridged across

the shotcrete-surface slab contact (Fig. C-2). Although some samples failed

C-1

FIGURE C-1 FRONT VIEW OF THE TESTING DEVICE AND / MONITORING SYSTEM

fIGURE C-2 SAMPLE ATTACHING SCHEME AND GAGE MEASURING STRAIN ACROSS THE CONTACT

C-2

' t

•

along weaknesses (laminations) in the shotcrete, most failures occurred

along the shotcrete-slab contact (Fig. C-3).

FIGURE C-3 FAILED ADHESIVE TEST SAMPLE

C-3

TABLE C-2

SUMMARY OF ADHESION-TEST RESULTS

Test no. Sample Test Hours between Hours of no. hours cutting & testing curing

Adhesion value psi (MPa) Remarks

S-9 & S-10 T-lA* 144 0 144 144.7 (1.0) Cured in crane bay

T-2A* 144 0 144 ' 164.4 (1.13) Cured in crane bay

T-3A* 144 0 144 142.6 (0.98) Cured in crane bay

T-4A* 144 0 144 160.0 (1.10) Cured in crane bay

T-5A* 144 0 144 158.8 ( 1 . 09) Cured in crane bay n I

O'\ I = 770. 5

Avg= 154.0 (1.06)

* Samples obtained from center section, tested on June 4, 1975

-TABLE C-3


Sample Test Hours between Hours of Adhesion value Test no. no. hours cutting & testing curing psi (MPa) Remarks

S-7 & S-8 S-1 7 0 24 86.8 (0.60)

S-2 7 0 24 l 08. l (0.75)

S-3 7 0 24 92.3 (0.64)

S-4 7 0 24 73. l (0.50)

("") S-5 7 0 24 83.9 (0. 581 I .......

S-6 7 0 24 65.3 (0.45)

S-7 7 0 24 73.4 (0.51)

S-8 7 0 24 87.6 (0.60)

S-9 7 0 24 111. 8 (0.77)

S-10 7 0 24 40.7 (0.28)

E = 823

Avg= 82 ( 0. 57)

--

TABLE C-4 ---


Sample Test Hours between Hours of Adhesion value Test no. no. hours cutting & testing curing psi {MPa) Remarks

S-11 & B2 7 24 8.4 (0.06) S-12

C2 7 24 81.2 (0.56)

D2 7 24 38.6 (0.27)

E2 7 24 15 . 4 (0.11)

-- ('") I F3 7 24 7.2 (0.05) co

Excluding B2 & F3; I = 135. 2 (0.31)

Avg= 45

-

Axial displacements (µm)

0 2.5 5.0 7.5 10.0 12.5 15.0 17. 5 20.0

6

1250 ----r------,r-----,----,----,-----,----,---7

5r 100

\ ,oooL ( Sample C 2 Sectional area= 5.20 in.

I I I I 4

I 750

........ ........

~ 3 Vl

.Cl ,--

n ----I -0 <..O '° -0

0 <ti .....J 0

.....J 500

2

250

0 Ou...---....1..----~-----'-----...___....;;;;:::....__,, ____ -'----__,j-------' 0 l 2 3 4 5 6 7 8

Axial displacements (l0-4 in.)

FIGURE C-4 LOAD VS CONTACT DISPLACEMENTS RELATIONSHIP OBTAINED FROM ADHESIVE TESTS

Axial displacements (µm)

0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 --t

6

1250---------,-----,------r-----,-----.---,---7

5

I 1000 S-9 T

I Sectional area= 3.93 in. 2

4

~ , ........ .750 .::,,t. Vl

----- ..0 n -0 3 ~ I __, ~

0 0 ,~ _J

0 _J

500 I

2

250

0 l 2 3 4 5 6 7 8

Axial displacements (10-4 in.

FIGURE C-5 LOAD VS CONTACT DISPLACEMENTS RELATIONSHIP OBTAINED FROM ADHESIVE TESTS

EFFECT OF SAMPLE SIZE

Tests were conducted to determine the effect of sample size on

adhesion measurements. These test results indicate that a minimum cross

sectional area of 2 in. x 2 in. (5.1 cm x 5.1 cm) is necessary to avoid

reductions in the adhesive strength created by the shrinkage of the shot

crete layer.

These shrinkage effects can be minimized if the samples are kept

intact during curing and if they are prepared immediately prior to testing.

Vibration caused by the saw can also disturb the shotcrete-slab bond contact

and can diminish the adhesive strength. The disturbance created by the saw

can be reduced by precutting the surface slab, binding the cut pieces to

gether and spraying shotcrete on the slab mosaic. The samples are prepared

by sawing the shotcrete along the precut sides of the slab sections. This

technique works very well for obtaining samples with young shotcrete or

having poor shotcrete-slab bond. The adhesive strength values shown in

Tables C-1 to C-4 are probably lower than the actual adhesion developed in

the model.

* U . S. GOV ER NMENT PRINTING OF FICE: 1976 - 21 1 · 173/486

C-11

-

, . ,• I

Date post:	23-Mar-2021
Category:	Documents
Upload:	others
View:	7 times
Download:	0 times

SHOTCRETE STRUCTURAL TESTING OF THIN LINERS -...

Documents