7~~CO MISCELLANEOUS PAPER GL-88-28

i AXIAL RESPONSE OF THREE VIBRATORY ANDof EngneersTHREE IMPACT DRIVEN H-PILES IN SAND

by

AD-A199 126 Larry M. Tucker, Jean-Louis Briaud

Briaud Engineers1805 Laura Lane

College Station, Texas 77840

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Final Report

M Approve~d For Public Release. Distribution Unlimited

DTICELECT

SEVO 21988H

Proparod tor US Army Engineer DivisionLower Mississippi Valley

Vicksburg, Mississippi 39180-0080Undnr Contract No. DACW39-88-MO-421

or-itored by Geotechnical LaboratoryUS Army Engineer Waterways Experiment Station

LABORATOR P0 Box 631, Vicksburg, Mississippi 39180-0631

88 9 2 0 5

Destroy this report when no longer needed. Do not returnit to the originator.

The findings in this re1 ort are not to be construed as an officialDepartment of the Army position unless so diesignated

by othe - authorized documents.

The contents of thi. report aTe 01, toC be Used foCI

advertising, publicationf, or prornotioral purooseS.

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distribution unlimited4. PERFORMING ORGANIZATION REPORT NUMBER(S) S. MONITORING ORGANIZATION REPORT NUMBER(S)

Miscellaneous Paper GL-88-28

6a NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION(if applicable) USAEWES

Briaud Engineers Geotechnical Laboratory6c. ADDRESS (City, State, and ZIP Code) 7b. ADDRESS (City, State, and ZIP Code)

1805 Laura Lane PO Box 631College Station, TX 77840 Vicksburg, MS 39180-0631

Ba. NAME OF FUNDING/ SPONSORIG_ - b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBERORGANIZATION (If applicable)

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PROGRAM PROJECT TASK WORK UNITELEMENT NO. NO. NO. CCESSION NO.

See Reverse I I I F11. TITLE (Include Security Classifncaion)

Axial Response of Three Vibratory and Three Impact Driven H-piles in Sand12. PERSONAL AUTHOR(S) ' 'Tucker, Larry M.; Briaud, Jean-Louis

13a. TYPE OF REPORT i3b. TIME COVERED 14. DATE OF REPORT (Vear,AonthOay) 15. PAGE COUNTFinal report FROM TO August 1988 78

16. SUPPLEMENTARY NOTATIONAvailable from National Technical Information Service, 5825 Port Royal Road,Springfield, VA 22161

17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)FIELD GROUP SUB-GROUP Axial loading, Impact hammers, S

H-piles Vibratory hammers . q

19, A!I ACT (Continue on reverse if necessary and identify by block number)

A research program to compare the ultimate axial capacity of vibratory and impactdriven H-piles in sand was conducted at a San Francisco, CA, site. The effects of time-lapse after driving was also studied. The piles were instrumented so that both pile tiploads and load transfer along the pile could be determined. ., " . . "'-.

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DO Form 1473, JUN 86 Previous editions are obsolete. SECURITY CLASSIFICATION OF THIS PAGE

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89CUOIV CILAIFICA1ON OF THIS RZafE

8a. & 8c. NAME AND ADDRESS OF FUNDING/SPONSORING ORGANIZATIONS AND ADDRESSES (Continued).

US Army Engineer Division, Lower Mississippi ValleyP0 Box 80Vicksburg, MS 39180-0080

Unclasifie

SICIAITYCLASIFIATIO OFTHISPAG

PREFACE

This report was prepared by Mr. Larry M. Tucker and Dr. Jean-Louis -

Briaud, College Station, Texas, under contract to the US Army Engineer Water-

ways Experiment Station (WES), Vicksburg, Mississippi, for the US Army Engi-

neer Division, Lower Mississippi Valley. The report was prepared under Con-

tract No. DACW39-88-MO-421.

This report was reviewed by Mr. G. Britt Mitchell, Chief, Engineering

Group, Soil Mechanics Division (SMD), Geotechnical Laboratory (GL), WES.

General supervision was provided by Mr. Clifford L. McAnear, Chief, SMD, and

Dr. William F. Marcuson III, Chief, GL.

COL Dwayne G. Lee, EN, is Commander and Director of WES. Dr. Robert W.

Whalin is Technical Director.

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TABLE OF CONTENTS

Page

BACKGROUND. .............................. 1

THE SOIL. ............ ................... 3

THE PILES AND LOAD TEST PROCEDURES ................... 11

LOAD TEST RESULTS...........................19

Residual Stresses ......................... 19Load Test Results ......................... 19Pile Driving Analyzer Results ................... 52

DISCUSSION OF THE RESULTS.......................53

Top Load-Settlement Curves....................53Load Distribution ......................... 56Load Transfer ........................... 58Effect of Time.................... . .. 58

CONCLUSIONS AND RECOMMENDATIONS....................66

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LIST OF FIGURES

Figure Page

i Location of Borings and Instrumentation ... ........ 4

2 Profiles of Standard Penetration Test Blowcounts .... 5

3 CPT Profiles for Point Resistance ..... ........... 6

4 CPT Profiles for Friction Resistance ..... .......... 7

5 Net Limit Pressure Profile ....... ............... 8

6 First Load Modulus Profile ....... ............... 9

7 Reload Modulus Profile ........ ................. 10

8 Location of Pile Instrumentation ..... ............ 12

9 Test Pile Locations ...... .................. . 13

10 Impact Pile Driving Records ..... .............. . 17

11 Vibratory Pile Driving Records .... ............. ... 18

12 Load-Settlement Curve for Pile 1I ... ........... . 21

13 Raw Load Versus Depth Profiles for Pile 1I ........ ... 22

14 Corrected Load Versus Depth Profiles for Pile 1I .... 23

15 Interpreted Load Versus Depth Profiles for Pile 1I 24

16 Friction Versus Movement Curves for Pile 1I . ...... . 25

17 Point Resistance Versus Movement Curve for Pile 1I 26

18 Load-Settlement Curve for Pile IIR ... ........... ... 27

19 Raw Load Versus Depth Profiles for Pile IIR ...... ... 28

20 Corrected Load Versus Depth Profiles for Pile IIR 29

21 Interpreted Load Versus Depth Profiles for Pile IIR 30

22 Friction Versus Movement Curves for Pile fIR ........ ... 31

23 Point Resistance Versus Movement Curve for Pile fIR 32

24 Load-Settlement Curve for Pile 1V ... ........... . 33

25 Raw Load Versus Depth Profiles for Pile 1V ......... ... 34

iv

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Figure Page

26 Interpreted Load Versus Depth Profiles for Pile IV . 35

27 Friction Versus Movement Curves for Pile IV . ...... . 36 %

28 Point Resistance Versus Movement Curve for Pile IV 3. . 37

29 Load-Settlement Curve for Pile lVR ... ........... ... 38

30 Raw Load Versus Depth Profiles for Pile lVR . ...... . 39

31 Interpreted Load Versus Depth Profiles for Pile lVR 40 0

32 Friction Versus Movement Curves for Pile 1VR ........ . 41

33 Point Resistance Versus Movement Curve for Pile lVR 42

34 Load-Settlement Curve for Pile 21 ... ........... . 43 0

35 Raw Load Versus Depth Profiles for Pile 21 ........ . 44

36 Corrected Load Versus Depth Profiles for Pile 21 . .. 4. 45

37 Interpreted Load Versus Depth Profiles for Pile 21 45 .. ,

38 Friction Versus Movement Curves for Pile 21 . ...... . 47 O

39 Point Resistance Versus Movement Curve for Pile 21 . 48

40 Load-Settlement Curve for Pile 2V ... ........... . 49

41 Load-Settlement Curve for Pile 31 ... ........... . 50 %

42 Load.3,tlemeut CuA.re foi rile 3V ..... ........... 51

43 Comparison of Load-Settlement Curves .. .......... ... 54

44 Friction Versus Depth Profiles .... ............. ... 57

45 Comparison of Point Load Transfer Curvez.. .......... 59

46 Normalized Point Load Transfer Curves .. ......... . 60

47 Normalized Friction Transfer Curves for ImpactDriven Piles ........ ...................... . 62

48 Normalized Friction Transfer Curves for VibratoryDriven Piles ........ ...................... . 63

49 Pile Capacity at 0.25 in Settlement Versus Time . . . . 64

50 Pile Ultimate Capacity Versus Time ... ........... ... 64

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LIST OF TABLES

Table Page

1 Load Test Program Summary ................. 15

2 Specifications for Delmag D22 Impact Hammer ........ 16

3 Specifications for ICE-216 Vibratory Driver ........ 16

4 Pile Driving Analyzer Results ............... 52

5 Analysis of Pile Test Results ............... 55

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BACKGROUND

In the spring and summer of 1986 a series of vertical load tests

were carried out on instrumented piles driven in sand at Hunter's Point

in San Francisco. The Federal Highway Administration sponsored two

projects on impact driven piles: one on the testing of five single piles

and one on the testing of a five pile group (Ng, Briaud, Tucker 1988a;

1988b). Then, the Lower Mississippi Valley Division (LMVD) of the Corps 4

A4.of Engineers operating through the USAE Waterways Experiment Station

(WES) sponsored a project on the comparison of impact driven piles and

vibratory driven piles. Subsequently, the Deep Foundation Institute

drove a number of piles with various vibratory hammers to compare the Jft,

hammers' efficiencies.

- This report is an analysis of the pile load tests-sponsored by the

LMVD through WES comparing impact and vibratory driven piles. The site A

is characterized, the load tests are described, the load tests results

are analyzed and discussed, and recommendations and conclusions are

made.

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THE SOIL

The soil has been described in detail by Ng et al. (1988a). Below

a 4 in thick asphalt concrete pavement is a 4.5 ft thick layer of sandy

gravel with particles up to 4 inches in size. From 5 ft to 40 ft depth

is a hydraulic fill made of clean sand (SP). Below 40 ft, layers of

medium. stiff to stiff silty clay (CH) are interbedded with the sand down

to the bedrock. The fractured serpentine bedrock is found between 45 ft

and 50 ft depth. The water table is 8 ft deep.

Many tests have been performed at the site including: standard

penetration tests with a donut hammer and a safety hammer, sampling with

a Sprague-Henwood sampler, cone penetrometer tests with point, friction

and pore pressure measurements, preboring and selfboring pressuremeter

tests, shear wave velocity tests, dilatometer tests and stepped-blade

tests. The CPT, SPT and stepped-blade tests were performed before and

after driving and testing of the FHWA test piles. The location of sel-

ecte-d soundings are shown on Figure 1. The corresponding profiles are

shown on Figures 2 through 7. The hydraulic fill has the following

average properties:

Friction angle 320 to 350Water content 22.6 %

Dry unit weight 100 pcf

D60 0.8 mm

D10 0.7 mmSPT blow count 15 bpfCPT tip resistance 65 tsf

PMT net limit pressure 7 tsfShear modulus (from shearwave velocity measurements) 400 tsf

3

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C CONE PENETROMETER TESTSD DILATOMETER TESTSE EXTENSOMETERP PIEZOMETERPM PREBORING PRESSUREMETER TESTSSP SELFBORING PRESSUREMETER TESTS

Figure 1. Location of Borings and Instrumentation

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SPT N VALUE (BLOWS/PT)

0 10 20 30 40 so 60

5

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15BoigB

20 X_ y. Average N Value

_SPT Tests Per-formed with aDonut Hammer.

25

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454

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CONE TIP RESISTANCE (kef)

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25 formed with a

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Figure 3. CPT Profiles for Point Resistance

6

LOCAL CONE FRICTION (kef)

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100

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CPT Tests Perfor-c. med with Standard

Electric Cone.

400

45

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Figure 4. CPT Profiles for Friction Resistance

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NET LIMIT PRESSURE P1* (kPo)

0 250 500 750 1000 1250 1500

0

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0. 30w

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8

FIRST LOAD MODULUS Eo (MPa)

0 2 4 6 8 100

5 ~-4PBPMT E

PRESSUREMETER10

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Figure 6. First Load Modulus Profile

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RELOAD MODULUS Er" (MPa)

0 10 20 30 40 50 60 70 80 go 1000

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5 0 ......... 00 SBPMT E

-------- - SBPMT Er

10 PRESSUREMETER

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Figure 7. Reload Modulus Profile

10I

THE PILES AND LOAD TEST PROCEDURES

Three HP14x73 steel H piles were used in this program. They were -

all embedded 30 ft below the ground surface; however, a 4.5 ft deep, 14

in diameter hole was drilled prior to pile insertion for the impact

driven piles, making the true pile embedment equal to 25.5 ft. For the

vibratory driven piles a hole was drilled through the 4 in thick asphalt

layer only, making the embedment equal to 29.5 ft. Each pile had two %

angles (2.5 x 2.5 x 3/16 inches) welded to the sides of the pile we' as

protection for the instrumentation.

The first pile was one of the single piles used in the FHWA program

(referred to as pile 1). Pile 1 was instrumented with seven levels of

strain gauges and a tell tale at the pile tip (Figure 8). This pile was

calibrated before driving and the pile stiffness was measured for use in

the data reduction. The measured value of pile stiffness (AE) was

614908 kips. This value was used for all three piles. Pile driving

analyzer measurements were obtained during the driving of pile 1 with an

impact hammer. Pile 1 was then load tested in compression 30 days after

it was driven (FHWA program): this is load test 1I. Pile I was then

retested at 67 days after driving: this is load test IR. After pile 1

was retested, the pile was restruck with an impact hammer and pile driv-

ing analyzer measurements were obtained. Pile I was then extracted and

vibrodriven about 30 ft from the impact test (Figure 9). It was load

tested at 33 days after driving (load test IV) and again at 63 days

after driving (load test IVR). After load test IVR the pile was struck

with an impact hammer and pile driving analyzer measurements were ob-

tained.

111

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TALESTRAINGAGES

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1",, /, ,- ./ .

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Figure 8. Location of Pile Instrumentation

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The second pile (Pile 2) was instrumented with two levels of strain

gauges: one at the mid-point and one at the pile tip (Figure 8). Pile 2

was impact driven and tested at 65 days after driving: this is load test

21. Pile 2 was then extracted and vibrodriven and tested at 64 days

after driving. This is load test 2V. After load test 2V, the pile was

struck with an impact hammer and pile driving analyzer measurements were

obtained.

The third pile (Pile 3) was not instrumented. It was impact driven

and tested at 12 days after driving: this is load test 31. Pile 3 was

then extracted and vibrodriven. It was tested at 12 days after driving:

this is load test 3V. Table 1 summarizes the eight load tests presented

in this report.

The impact driven piles were installed using a Delmag D22 diesel

hammer at full throttle. All restrike measurements were also obtained

using this hammer. The hammer was rated at approximately 40,000 ft-lbs

maximum energy. Details of the hammer are given in Table 2. The driv-

ing records for the impact driven piles are shown in Figure 10.

The vibratory driven piles were installed with a ICE-216 vibratory

hammer. Details of the hammer are given in Table 3. The penetration

rates versus depth records for these piles are shown in Figure 11.

The load test procedure has been described in detail by Ng et al.

(1988). In general, the test loads were applied in increments of 10

percent of the estimated ultimate load. Each load step was held for at

least 30 minutes, with the load being monitored continuously. All read-

ings from electronically monitored instruments were recorded every 5

minutes. The data was stored on floppy disk for data reduction.

14

IN "

Table 1. Load Test Program Summary

Test Piles

II - FHWA Pile (Impact) 30 Day test

IR - FHWA Pile (Impact) 67 Day test

lV - FHWA Pile (Vibratory) 33 Day test

lVR - FHWA Pile (Vibratory) 63 Day test

21 - New Pile (Impact) 65 Day test

2V - New Pile (Vibratory) 64 Day test

31 - New Pile (Impact) 12 Day test

3V - New Pile (Vibratory) 13 Day test

Notes: , j ,

A. 1I, hIR, 1V and lVR - Seven strain gauge levels 'J

B. 21 and 2V - Two strain gauge levels

C. 31 and 3V - No strain gauges c-A,

15

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Table 2. Specifications for Delmag D22 Impact Hammer

Rated energy 39,700 ft-lbsRam weight 4,850 lbsBlows/minute 42-60

Maximum explosivepressure on pile 158,700 lbs

Working weight 11,275 lbs

Drive Cap weight 1,500 lbs

V

Table 3. Specifications for ICE-216 Vibratory Driver

Eccentric moment 1000 in-lbsFrequency 400-1600 vpm

Amplitude 1/4 - 3/4 inches

Power 115 hPPile clamping force 50 tonsLine pull for extraction 30 tons .Suspended weight with clamp 4825 ibs N

Length 47 inches '

Width 16 inchesThroat width 12 inchesHeight with clamp 78 inches-.Height without clamp 68 inches

16

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PENETRATION BLOWCOUNT (blows/f t) )

(ft) PILE 1 PILE 2 PILE 3 ,

1 RUN NA* RUN2

3

464

10 1 41P 2 412 2 4

13 3 414 2 415 2 4

16 2 417 2 5

18 2 419 2 420 2 6

21 2 622 4 623 6 624 5 825 7 826 7 9'

27 8 0

28 0 9

29 21 4130 12 61

TOTAL 96 131,'r

*Not available ;

Figure 10. Impact Pile Driving Records

22 4 6

17 8

'630 12-11

'.' -',- ,,r- :, -l , , . L • ,.l" ,- - . . ' ' ', • , ' "-" :' " . " . . " ,: - " - .0 .

Pile 1 Pile 2 Pile 3

Rate of Rate of Rate of

Depth Time Penetration Time Penetration Time Penetration

(ft) (sac) (ft/min) (sac) (ft/min) (sac) (ft/min)

0

1

2 03

5 1.9

6

7 6.7 25.0

8

9 4 15

10 12 10 9 12

11 12.2 43.6 18 12 14 12

12 23 12 19 12

13 16.8 26.1 28 10 23 15

14 22.7 10.2 34 12 29 10 015 28.4 10.5 39 12 34 12

16 34.6 9.7 44 12 38 15

17 39.0 13.6 49 12 42 15

18 45.1 9.8 54 12 46 15

19 58 15 49 20

20 63 12 53 15

21 57.2 14.9 66 20 58 12

22 61 15.8 69 20

23 73 15 61 40?

24 76 20 64 20

25 70 20 79 20 67 20

26 83 15 70 20 •

27 86 20 73 20

28 89 20 76 20

29 92 20 80 15

30 85 20 96 15 85 12

Figure 11. Vibratory Pile Driving Records

18

LOAD TEST RESULTS

Residual Stresses

Residual driving stresses were measured for pile 11. The stress

profile was not monitored between load test 1I and test IIR. Therefore

the residual stress profile after driving was also used for load test

IIR. Since additional residual stresses are usually induced due to a

compression test, this profile is slightly in error. The residual

stress profile is the first load profile shown in Figure 14.

An attempt was made to record the residual driving stresses for

pile 21. However, the readings obtained were judged unreliable. There-

fore, the residual stress profile from pile II was used in reducing the

load test data for pile 21 (Figure 14).

The vibratory driven piles were assumed to have no residual driving

stresses. No attempt was made to verify this. However, published data

substantiate this assumption (Hunter and Davisson, 1969). "

Load Test Results

The raw data from the floppy disks was reduced to obtain the fol-

'owing information:

Load-settlement curve at the pile top

Load versus depth profiles - a. raw data

b. including residual loads

c. interpreted profile

Load transfer curve (friction and point)

The number of plots possible for a given load test depends upon the

amount of instrumentation on the pile.

As stated above, three sets of load versus depth profiles are plot-

ted for those piles instrumented with strain gauges. The first set of

19

-V

profiles will be the raw data as measured during the test. Since all

instrumentation was zeroed just before the load test, these profiles do

not include residual stresses.

A second set of profiles is shown for those piles driven with an

impact hammer which include the residual loads in the pile due to driv-

ing. This set of profiles is not shown for the vibratory driven piles

since it has been assumed that no residual stresses are induced due to

installation.

The third set of profiles is the interpreted load versus depth

curves. The measured data shows some irregularities which may be due to

drift in the readings, temperature fluctuation or gauge malfunction. A

gauge reading was omitted entirely if it was known that the gauge was

definitely malfunctioning. This was the case with the gauge at a depth

of 25 ft for pile IV and IVR, and for both gauge levels on pile 2V. Any

other irregularities were smoothed by fitting a second order polynomial

curve through the data. These curves are shown as the third set of load

versus depth profiles. Other interpretations are obviously possible.

However, the fit of the curves matches quite well with what one would

draw manually.

The results for load test 1I are given in Figures 12 through 17;

load test IR results are shown in Figures 18 through 23; load test IV

results are shown in Figures 24 through 28; load test 2VR results are

shown in Figures 29 through 33; load test 21 results are shown in Fig-

ures 34 through 39. Load-settlement curves at the pile top are shown in

Figures 40 through 42 for load tests 2V, 31 and 3V respectively.

20

TOP LGO (KIPS)

a 50 100 I50 200

PILE 1.5- IMPACT

30 DAY TEST

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37

TOP LOAD (KIPS)

O 5o I00 150 200

PILE IVIBRATORY63 DAY TEST

zwxw-j

W) 1.5

2 -

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Figure 29. Load-Settlement Curve for Pile MV

38

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PILE 2IMPACT

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S PILE 2VIBRATORY54 DAY TEST

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50

TOP LOAD (KIPS)

a so 100 I50 2000

PILE 3-5 VIBRATORY

13 DAY TEST

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I-51

Pile Driving Analyzer Results

The pile driving analyzer (PDA) consists of the dynamic monitoring

of strain gauges and accelerometers attached to the pile close to the

top. The strain measurements are used to obtain force measurements as a

function of time, and the accelerometer measurements are integrated to

obtain velocity versus time. From these two measurements various para-

meters may be calculated, including the maximum energy delivered to the

pile and the static resistance of the pile by the CASE method (Rausche

et al., 1985). This static resistance represents the PDA capacity pre-

diction.

Pile driving analyzer measurements were made on pile 1 (driven with

the impact hammer) for both initial driving and for restrike after the

load tests were performed, and on piles 1 and 2 (driven with the vibra-

tory hammer) for restrike after the load tests were performed. The

results are presented in Table 4.

Table 4. Pile Driving Analyzer Results

(from Holloway, 1987)

Pile Blowcount Maximum Maximum EstimatedForce Energy Capacity*

(kips) (kip-ft) (kips)

li** 12/12 in. 340-510 5-15 140-165

ii*** 6/6 in. 350-505 10-17 145-200

IV*** 7/6 in. 300-415 4-13 120-140

2V*** 14/12 in. 355-520 5-11 125-150

S* Case method capacity assumes a damping constant J=0.25

** Initial driving*** Restrike

52

,P

DISCUSSION OF THE RESULTS

Top Load-Settlement Curves •

The top load-settlement curves for the eight load tests are shown

together in Figure 43. Two main observations can be made. First, in

all cases the vibratory driven piles have a lower initial stiffness than

the impact driven piles. Second, the impact driven piles show more

consistent response between piles than the vibratory driven piles.

In an effort to quantify these observations four measurements have •

been made from the load-settlement curves. First, the ultimate load has

been defined as the load corresponding to a settlement of one-tenth of

the equivalent pile diameter plus the elastic compression of the pile

under that load as if it acted as a free-standing column. This line has

been drawn on Figure 43. Second, the load at a settlement of 0.25 in

has been obtained from the load-settlement curves. Third, the settle-

ment at one-half the defined ultimate load has been obtained. Fourth,

the piles' stiffness response has been calculated as one-half the de-

fined ultimate load divided by the settlement occurring at that load..rg-,.

These four items are tabulated in Table 5 for the eight load tests.

Table 5 shows that there is only one percent difference in the

average ultimate load between the impact driven piles and the vibratory

driven piles. However, the coefficient of variation of the ultimate

loads for the vibratory driven piles is 4.3 times higher than that of

the impact driven piles.

The second column of Table 5 shows that at a settlement of 0.25 in

the impact driven piles carry 33 percent more load than the vibratory '"

driven piles. The coefficient of variation of this load for the vibra-

53

f % % A

TOP LOD (KIPS)

0 50 100 150 200

22

I-I

-NJ

.5

I VR

.j 2V

1.54

D/1 +. N.. - . "'N/ AS *S N

Table 5. Analysis of Pile Test Results

Pile Load at Load at Settlement at InitialD/10 + PL/AE 0.25 in. Qult/2 Stiffness

(kips) (kips) (in) (kips/in) .'

II 160 120 0.104 769

IIR 170 126 0.094 904 P6%

21 175 131 0.088 994

31 160 120 0.088 9,,9

Average 166 124 0.094 894

Standard

Deviation 7.5 5.3 0.0075 93

Coefficientof Variation 0.045 0.043 0.081 0.104

1V 180 102 0.181 497

IVR 145 110 0.103 704

2V 130 71 0.184 353

3V 200 90 0.313 319

Average 164 93 0.195 468

StandardDeviation 32 17 0.087 175

Coefficientof Variation 0.195 0.182 0.446 0.374

Impact1.01 1.33 0.48 1.91

Vibratory

55

tory driven piles is 4.2 times higher than that of the impact driven

piles.

The settlement at one-half the ultimate load for the vibratory

driven piles is over two times larger than that of the impact driven

piles, and the coefficient of variation is 5.5 times larger.

The initial stiffness response of the pile, defined as one-half the

ultimate load divided by the settlement at that load, for the impact

driven piles is 1.91 times that of the vibratory driven piles. The

coefficient of variation of this stiffness for the vibratory driven

piles is 3.6 times that of the impact driven piles.

Load Distribution

The load distribution of the vibratory driven piles differs greatly

from that of the impact driven piles. By comparing Figures 15, 21, 26,

31, and 37 it can be seen that at maximum load the impact driven piles

carry approximately 51% of the load in point resistance, whereas the

vibratory driven pile carries only 13% of the load in point resistance.

The reload test on the vibratory driven pile (Figure 31) shows that the

point resistance has increased to 29% of the total load. This indicates

that the difference in the driving process causes a different soil

reaction, but the difference becomes less upon repeated loading.

The unit friction profiles at maximum loading are shown in Figure

44 for the five instrumented pile tests. Again in can be seen that

there is a definite difference in soil reaction between the impact

driven and vibratory driven piles; and that the difference becomes less a

pronounced upon repeated loading.

56

In

/ ,S-.c

,-4.

"+ 41°< ", /

> /A>

Zw 1 /_1

,4"4

i"

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O0 J 0 I l 0 I 1 0 '

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57.

-- - ---/ %

Load Transfer

The H-pile presents a problem when computing unit tip resistance

and unit friction values: WVIdL is the failure surface? One possible

assumption is that the pile fails along a rectangle which encloses the

H-pile, with a soil plug forming between the flanges. Another possibil-

ity is that the pile fails along the soil-pile interface, with no soil

plug forming. Previous research has shown that a better assumption may

be that the failure surface is in between the previous two assumptions

with a soil plug filling half the area between the flanges (Ng et al.,

1988). For the HP14x73 piles used in this study this assumption gives

.2the following properties: Perimeter - 70.47 in, Tip area = 109.8 in

This assumption is used for all further analyses.

Figure 45 shows the unit tip resistance versus tip movement curves

for the five instrumented piles. Figure 46 shows the same curves with

the tip resistance normalized by dividing by the maximum tip resistance.

These two figures show a fundamentally different reaction between the

vibratory driven piles and the impact driven piles: The tip resistance

of the vibratory driven piles is much lower than that of the impact

driven piles, and the slope of the curve is different. However, the

difference in shape almost vanishes upon reloading.

The shape of the tip resistance curve of the initial loading of the

vibratory driven pile suggests that the sand immediately under the pile

point is initially loose but densifies as the pile is laded. Indeed,

at higher loads the tip resistance begins to increase at a faster rate,

rather than reaching a limiting value as the other tests show. By com-

paring the curves for Pile 11 and lIR, it can be seen that the impact

58

* A. j6

-~~~ ~~~~~ r.~- -. . - .

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driven piles do not undergo such a change in behavior between initial

loading and reloading.

Figures 47 and 48 show the normalized friction movement curves for

the impact driven piles and vibratory driven piles, respectively. Fig- 'r

ure 47 shows again that the impact driven piles are very consistent in

their response and that no change in behavior occurs between initial

loading and reloading. However, Figure 48 shows that the vibratory

driven pile exhibits a great change in behavior between initial loading

and reloading. The five curves for the initial loading have a much

softer initial response than the reloading curves. Also the initial

loading curves become softer as the depth increases, whereas the reload

curves become stiffer as the depth increases. The reloading curves also

exhibit a pattern which matches the impact driven piles very well.

Effect of Time

Piles 1I and 1V were tested about 31 days after driving and then

retested about 65 days after driving. The plots of ultimate load versus

time for two criteria are shown in Figures 49 and 50. The trend given

by those two figures does not allow to conclude that there is an

increase in capacity versus time. Indeed Figure 49 shows an increase in

stiffness but Figure 50 shows a decrease in capacity for the vibratory

driven piles; for the impact driven piles Figure 49 shows an increase

while Figure 50 shows a slight increase. At Lock and Dam 26 the

capacity obtained in the load test was 67% higher than the capacity .

predicted by the wave equation method on the average. This can be. I-.

explained by a 67% average gain in capacity of the piles between driving

and load testing of the piles (1 week). Note that the sand at Lock and

61

* b. -- - In

____ ____ ____ ____ ____ ____ __ I-~1**~* . ( I ' 'I I I0

N4

U,

uw I

'-4

0 uw *

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300 ,1A

31 21 IR

- 100IVRwU) 3V

z x2V ?

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'"U.

w

oL 10 t I I a ,10 100 ,

TIME (DAYS)

Figure 49. Pile Capacity at 0.25 in Settlement Versus Time

300

I21

0.

LI

10 10

xa-L

1%2

-1 60

C

U

U %w

101II I

10 100

TIME (DAYS)

Figure 50. Pile Ultimate Capacity Versus Time

64

0Dam 26 had an average of 7.5% passing the #200 sieve while the sand at

Hunter's Point had 0% passing the #200 sieve.

In the case of Hunter's Point several factors influence the change

of capacity, one of which is the effect of time. The others include the

influence of soil heterogeneity and the influence of the first load test

on the second load test. In order to isolate the effect of time one

solution would be to use integrity testing to obtain the variation of

stiffness versus time. Another solution would be to use a series of r

load tests more closely spaced in time performed on the same pile over a

longer period of time (eg. I day, 4 days, 15 days, 40 days, 100 days).

.N

%'. ,.'.

654

N

65 1N%' ,~4.~.' W~ q ?

CONCLUSIONS AND RECOMMENDATIONS

The main conclusions to be drawn from this study are the following:

- Vibratory driving of piles leads to approximately the same

maximum load at large displacements, but to a larger settle-

ment at working loads.

- The load distribution is influenced greatly by the driving

process. For the piles in this study, impact driving led to a

point resistance which was 51% of the total load at maximum

loading compared to 13% for vibratory driving.

- The load transfer curves are also affected by the driving

process. Vibratory driving led to load transfer curves which

required much larger movements to reach maximum loading. This

accounts for the first conclusion above regarding larger set-

tlements at working loads being observed for vibratory driven

piles.

- The effects of vibratory driving listed above are lessened

upon reloading of the pile. Upon reloading, a vibratory dri-

ven pile carries a larger percentage of the load in point

resistance (29%) and the load transfer curves take on the same

shape as the impact driven piles.

- The data show that for impact driven piles there is a trend

towards a slight increase in capacity versus time. For

vibratory driven piles however, the data does not show any

clear trend.

66

The following recommendations are made based on the results of this

study:

- A series of load tests should be performed in a natural sand

deposit to verify the results found in this study. The test

program should include longer piles (at least 50 ft long) to

determine if the same behavior occurs.

An attempt should be made to load test piles which have been

installed with a vibratory hammer and then tapped with an

impact hammer. This procedure may yield the speed of install-0

ation of the vibratory hammer with the stiffer initial res-

ponse of the impact driven piles.

In order to isolate the effect of time on the variation of the

pile stiffness response integrity testing could be used. This

would have the advantage of being performed on the same pile,

and the loads are small enough not to change the soil

structure around the pile.

* In order to isolate the effect of time on the variation of the

pile capacity a series of load tests more closely spaced in

time performed on the same pile over a longer period of time.

For example, a series of tests could be performed at 1 day, 4

days, 15 days, 40 days and 100 days after driving. This would

have the advantage of being performed on the same pile and

would include enough load tests to be able to assess the .,-,._

effect of one load test on subsequent load tests.

67%WAN

REFERENCES

Holloway, D.M., "Dynamic Monitoring Program Results, FHWA Vibratory

Hammer-Pile Testing, Hunters Point, California," Report to Geo/Re- 9

source Consultants, 1987.

Hunter, A.H., Davisson, M.T., "Measurements of Pile Load Transfer,"Performance of Dee, Foundations, ASTM STP 444, American Society for

Testing and Materials, 1969, pp. 106-117.

Ng, E.S., Briaud, J.-L., Tucker, L.M., "Pile Foundations: The Behavior

of Piles in Cohesionless Soils," FHWA Report FHWA-RD-88-080, 1988.

Ng, E.S., Briaud, J.-L., Tucker, L.M., "Field Study of Pile Group Action

in Sand," FHWA Report FHWA-RD-88-081, 1988.

Rausche, F., Goble, G.G., Likins, G.E., "Dynamic Determination of PileCapacity," Journal of Geotechnical Engineering, ASCE, Vol. 111, No.

3, March 1985. P

U,,

WR

68