Wedge Shear Testing of Soils An insufficiently utilized new technique Prof. Dr. Türker Mirata...

Wedge Shear Testing of SoilsAn insufficiently utilized new technique

Prof. Dr. Türker [email protected]

mailto:[email protected]

mailto:[email protected]

© Türker Mirata 2

METU Campus, 20 July 1966

A slip occurred

at the side of an

excavation for the

central heating

utilities of the campus

soon after the

excavation.

© Türker Mirata 3

This raised the QUESTION

Can one not devise a relatively simple test for pedicting, with fair accuracy, the safety of such slopes in stiff, fissured, unsaturated clays like the Ankara Clay?

The following 24 years saw to the development of three different versions of a testing technique which not only answers the above but also facilitates the shear testing of gravels and crushed rock.

© Türker Mirata 4

1. The in situ wedge shear test (iswest)

Suitable especially for unsaturated, stiff fissured and/or stony clays

Tried successfully on three slips in the Ankara Clay

© Türker Mirata 5

Principle of the iswest

© Türker Mirata 6

Loading mechanism

© Türker Mirata 7

Loading possible in any direction

© Türker Mirata 8

Different modes of loading

Different ways of measuring shear strength on a given plane by iswests.

© Türker Mirata 9

Six iswests carried out at Site C/1

7-23 June 1971; iswests in pit 9m from 1968 slip

Note inclination of shear plane in different iswests, conforming with the failure surface in the actual slip.

© Türker Mirata 10

Seven iswests carried out at Site D

30 May - 23 June 1972; in

pit close to 1966 slip

Note inclination of shear plane in different iswests, conforming with the failure surface in the actual slip.


Grooved loading plates and ball cage


Comparison of the shear plane areas

60 mm dia. shear box

360 mm x 250 mm iswest mould


All equipment used for the iswests


Test moulds used for the iswests

Two moulds are enough for most purposes.


Jack may be raised during the test

Jack raised by actuating the vertical screw


Earlier loading setup

Load applied on face of test mould through steel balls and a loading plate


Improved loading setup

Load applied through two grooved plates with steel balls in between


Shoring for vertical iswests & slip plane

A slip occurred during the rainy season following these iswests

Vertical loading applied at these points


Vertical loading on side of cut

Iswest with vertical loading


The shoring after the slip

This type of shoring proved unsuccessful

This showed it is safer to do such tests at the side of an adequately supported test pit.


Preparing for iswest in a test pit

Template used for shaping the loading pit


Sides of soil wedge being cut

L-shaped lamina used to aid this operation


Gauging stool for checking size of loading pit

Note the graduations on the legs for different

test moulds


Checking the size of the loading pit

Gauging stool in loading pit to be checked


The pivoting and jacking frame

Used for passing test mould over soil

wedge squarely


Marks on the cutting edges of test mould

These aid in positioning the test mould


Iswest in progress at bottom of pit

June 1971


Iswest in pit supported by expansible steel segments

Bent out of 3 mm thick

mild steel plate, eight

such 40 mm high

segments ranging

between 1035 and 1255

mm in dia. were used to

support a 4 m deep pit.


Comparison of factors of safety for three slips in the stiff fissured Ankara Clay

1.00 1.20 1.40 1.60

1.80 2.00 2.20 2.40

Slip 1 Slip 2 Slip 3

Fa

cto

r o

f s

afe

ty

Effective stress analysis based on triaxial tests on 36mm dia. specimens

Total stress analysis based on iswestsEffective stress analysis based on triaxial tests on 102mm dia. specimens


Comparison of the approximate time required for the different types of test

- 20 40 60 80

100 120

Slip 1 Slip 2 Slip 3Te

sti

ng

tim

e (

da

ys

)


Total stress analysis based on iswests



2. Cylindrical wedge shear test (cylwest)

Suitable for testing clayey tube samples up to about 100 mm in diameter, recovered from boreholes.

Suitlable for compaction control of clay fills.

Can be performed on clays or sands compacted directly in the cylwest mould.


Principle of the cylwest

The sample is introduced in a thin-walled steel tubecut at an angle between 30o and 45o to its axis. Upper half of mould is clampedin the cross-beam of an existing compressionmachine or portable frame. Spacers are removed. Loading is effected ina similar way to that in iswests.


Cylwest perfomed using a triaxial compression machine

The only modification is

to replace the cross-beam

by one that will accom-

modate the jaws used

for clamping the upper

half of the cylwest mould.


Cylwest performed using a portable frame

Easilycarried bytwo men,this frameenables on-site applica-tion of the test.


Loading in progress using portable frame

Sample

preparation

and testing

can be

completed

within one

hour.


Double-cut test mould

Used for testing compacted

soils in the same mould in

which they are compacted

One half of removed upper coupling


Compacting the soil in the double-cut mould

The mould is

attached to the

base plate

used in the

Proctor

compaction

test.


Cylwest in progress using the double-cut mould and a portable frame

One pair of couplings is

removed, and the sample

is sheared along the

exposed plane. The mould

is then re-assembled,

and the sample sheared

along the second plane.


Shear strength envelopes from cylwests and shear box tests on clays compared

Segments

of peak

strength

envelopes


Shear strength envelopes from cylwests and shear box tests on clays compared

Segments

of residual

strength

envelopes


Peak strength envelopes for compacted plastic clay at different water contents

3 % below optimum

At optimum

3 % above optimum


Peak strength envelopes for compacted sandy clay at different water contents

3 % below optimum

At optimum

3 % above optimum


Peak envelopes for compacted plastic clay at different compactive efforts

25 blows per

Layer

20 blows per

Layer

15 blows per

layer


Peak envelopes for compacted sandy clay at different compactive efforts

25 blows per

Layer

20 blows per

Layer

15 blows per

layer


Iswest with sub-lateral loading applied (lead to the develpoment of the priswest)

for keepingthe normalstressconstantafter thepeakstrengthis reached.


3. Prismatic wedge shear test (priswest)

Suitable for testing gravel, crushed rock, and clay with < 38 mm particles.

Enables static compaction to be applied for clayey samples.

Can be performed in the lab or on site within two hours.

Total weight of equipment needed is about 250 kg – ¼ of a conventional shear box for the same size of samples.


Principle of the priswest

The lateral loading device used in iswests ledto the devel-opment ofthe priswest.


Sample placement in priswest mould

The remov-

able lid is

temporarily

replaced by

a collar


Sample compaction in priswest mould

Kango

vibrating

hammer

being

applied on

gravel

sample.


Loading setup used for priswests (1)

The 5-toncapacityportableframe. Verticalloading is used for clay.


Loading setup used for priswests (2)

20-ton

capacity

frame.

Horizontal

loading is

used for

gravel.


Priswest in progress using 20-ton frame

Dial gauges

are used

to measure

displace-

ments.


Alternative devices for applying the lateral load in priswests

Air piston

Spring loaded piston


Static compaction of a gravelly clay

One of the advantages

of the priswest is that it

enables static compaction

to be applied using the

same 20-ton frame as

used during shear


Shear strength envelopes from priswests

Drained strength envelopes for crushed rock at two degrees of compaction, using moulds with differentangles


Comparison of priswests and triaxial tests on silty gravel (19 mm – 38 mm)

Drained triaxial tests

Priswests


Comparison of priswests and triaxial tests on crushed rock (< 38 mm)

Drained triaxial

tests

Priswests


Why should the results be so close?

The priswest, being close to plane strain conditions, would be expected to give a somewhat higher strength than the triaxial test.

Cylwests on sand do give a somewhat higher strength than the triaxial test.

The answer to this apparent anomaly is given in the next slide.


Plot of peak friction angles vs. angle between shear plane and bedding planes for six different sands

Cylwestswith abt.same as triaxialtests give higher

(deg)

Priswestshave lowerthan triaxial tests Angle between shear plane and bedding planes, (degrees)


Duration of priswests and triaxial tests

- 2 4 6 8

Gravel Crushed rock Gravelly clay(undrained

test)

Test

ing

time (

hour

s)

Triaxial tests on 190 mm samples

Priswests on 300 mm x 300 mm samples


Those who have helped investigate the different aspects of the wedge shear test:

Aybak, Turgut (M.Sc, 1988). Köseoğlu, Rüştü (M.Sc, 1988). Azimli, Fuat (M.Sc, 1989). Varan, Mustafa (M.Sc, 1989). Çağnan, Şener (M.Sc, 1990). Seçkin, Altan (M.Sc, 1993). Turp, Engin Zülfükar (M.Sc, 1993).


Those who have helped investigate the different aspects of the wedge shear test

(continued) Gökalp, Alp (M.Sc, 1994). Şakar, Mehmet (M.Sc, 1997). Gün, Fırat (M.Sc, 1997). Filiz, T. Emrin (M.Sc, 2000). Erzin, Yusuf (PhD, 2004).


Special thanks are due to

The many METU technicians who have made the special equipment.

The METU technicians who have helped during the testing.

All colleagues who have helped in different ways.

Last but not least, Dr. Murat Mirata for help in preparing this PowerPoint show.


THE END

Thanks for watching. For details see literature listed at http://www.metu.edu.tr/~mirata/

16 March 2007

http://www.metu.edu.tr/~mirata/

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Wedge Shear Testing of Soils An insufficiently utilized new technique Prof. Dr. Türker Mirata...

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