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Kuat Geser Tanah (Shear Strength)

- Triaxial Test -(Courtesy of COSC 323: Soils in Construction)

oleh:

 A. Adhe Noor PSH, ST., MTStaf Pengajar Progra Studi Te!ni! Si"il

#urusan Te!ni! $a!ultas Sains dan Te!ni!

%ni&ersitas #enderal Soediran

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Tria'ial Shear Test

Soil sa"le at

failure

$ailure "lane

Porous

stone

i"er&ious

e(rane

Piston )to a""l* de&iatoric stress+

Oring

"edestal

Pers"e'

cell

Cell "ressure

-ac! "ressure Pore "ressure or 

&olue change

ater 

Soil

sa"le

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Tria'ial Shear Test

Specimen preparation (undisturbed sample)

Sa"ling tu(es

Sa"le e'truder 

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Tria'ial Shear Test

Specimen preparation (undisturbed sample)

/dges of the sa"le are

carefull* tried

Setting u" the sa"le in

the tria'ial cell

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Tria'ial Shear Test

Sa"le is co&ered 0ith a

ru((er e(rane and

sealed

Cell is co"letel*

filled 0ith 0ater 

Specimen preparation (undisturbed sample)

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Tria'ial Shear TestSpecimen preparation (undisturbed sample)

Pro&ing ring toeasure the

de&iator load

1ial gauge to

easure &ertical

dis"laceent

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T*"es of Tria'ial Tests

s the drainage &al&e o"en

*es no

Consolidated sa"le

%nconsolidated 

sa"le

s the drainage &al&e o"en

*es no

1rained

loading

%ndrained 

loading

%nder allaround cell "ressure σc

σcσc

σc

σcSte" 4

de&iatoric stress

)∆σ 5 6+

Shearing )loading+

Ste" 2

σc σc

σc7 6

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T*"es of Tria'ial Tests

s the drainage &al&e o"en

*es no

Consolidated sa"le

%nconsolidated sa"le

%nder allaround cell "ressure σc

Ste" 4

s the drainage &al&e o"en

*es no

1rainedloading

%ndrained loading

Shearing )loading+

Ste" 2

C1 test

C% test

%% test

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Consolidated- drained test (CD Test)

Ste" 4: At the end of consolidation

σ8C

σhC

Total, σ 5 Neutral, u /ffecti&e, σ97

Ste" 2: 1uring a'ial stress increase

σ98C 5 σ8C

σ9hC 5 σhC

σ8C 7 ∆σ

σhC

σ98 5 σ8C 7 ∆σ 5 σ94

σ9h 5 σhC 5 σ93

1rainage

1rainage

Ste" 3: At failure

σ8C 7 ∆σf 

σhC

σ98f  5 σ8C 7 ∆σf  5 σ94f 

σ9hf  5 σhC 5 σ93f 1rainage

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1e&iator stress )6 or ∆σd+ 5 σ4 ; σ3

Consolidated drained test )C1 Test+

σ4 5 σ8C 7 ∆σ 

σ3 5 σhC 

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   8  o   l  u    e  c   h  a

  n  g  e  o   f   t   h  e

  s  a    "   l  e

   /  '  "  a  n  s   i  o  n

   C  o    "  r  e  s  s   i  o  n

Tie

8olue change of sa"le during consolidation

Consolidated drained test )C1 Test+

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   1  e  &   i  a   t  o  r  s   t  r  e  s  s ,

    ∆   σ   d

 A'ial strain

1ense sand or

OC cla*

(∆σd+f 

1ense sand orOC cla*

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C1 tests Ho0 to deterine strength "araeters c and φ

   1  e  &   i  a   t  o  r  s   t  r  e  s

  s ,

    ∆   σ   d

 A'ial strain

   S   h  e  a  r

  s   t  r  e  s  s ,

   τ

   σor   σ9

φMohr ; Coulo(

failure en&elo"e

(∆σd+fa

Confining stress 5 σ3a(∆σd+f(

Confining stress 5 σ3(

(∆σd+fc

Confining stress 5 σ3c

σ3c σ4cσ3a σ4a

)∆σd+fa

σ3( σ4(

)∆σd+f(

σ4 5 σ3 7 )∆σd+f  

σ3

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C1 tests

Strength "araeters c and φ o(tained fro C1 tests

Since u 5 in C1

tests, σ 5 σ9Therefore, c 5 c9

and φ 5 φ9

cd and φd are usedto denote the

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C1 tests $ailure en&elo"es

   S   h  e  a  r  s   t  r  e  s  s ,

   τ

   σor   σ9

φdMohr ; Coulo(

failure en&elo"e

σ3a σ4a)∆σd+fa

$or sand and NC Cla*, cd 5

Therefore, one C1 test 0ould (e sufficient to deterine φd of

sand or NC cla*

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C1 tests $ailure en&elo"es

$or OC Cla*, cd =

   τ

   σor   σ9

φ

σ3 σ4)∆σd+f 

c

σc

OC NC

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Soe "ractical a""lications of C1 anal*sis for

cla*s

τ τ 5 in situ drained shearstrength

Soft cla*

4. /(an!ent constructed &er* slo0l*, in la*ers o&er a soft cla* de"osit

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Soe "ractical a""lications of C1 anal*sis for

cla*s

2. /arth da 0ith stead* state see"age

τ 5 drained shear strength ofcla* core

τ

Core

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Soe "ractical a""lications of C1 anal*sis for

cla*s

3. /'ca&ation or natural slo"e in cla*

τ 5 n situ drained shear strength

τ

Note: C1 test siulates the long ter condition in the field.

Thus, cd  and φd  should (e used to e&aluate the longter (eha&ior of soils

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Consolidated- Undrained test (CU Test)

Ste" 4: At the end of consolidation

σ8C

σhC

Total, σ 5 Neutral, u /ffecti&e, σ97

Ste" 2: 1uring a'ial stress increase

σ98C 5 σ8C

σ9hC 5 σhC

σ8C 7 ∆σ

σhC   ±∆u

1rainage

Ste" 3: At failure

σ8C 7 ∆σf 

σhC

No

drainage

No

drainage

  ±∆uf 

σ98 5 σ8C 7 ∆σ > ∆u 5 σ94

σ9h 5 σhC > ∆u 5 σ93

σ98f  5 σ8C 7 ∆σf  > ∆uf  5 σ94f 

σ9hf  5 σhC > ∆uf  5 σ93f 

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   8  o   l  u    e  c   h  a

  n  g  e  o   f   t   h  e

  s  a    "   l  e

   /  '  "  a  n  s   i  o  n

   C  o    "  r  e  s  s   i  o  n

Tie

8olue change of sa"le during consolidation

Consolidated %ndrained test )C% Test+

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   1  e

  &   i  a   t  o  r  s   t  r  e  s  s ,

    ∆   σ   d

 A'ial strain

1ense sand or

OC cla*

(∆σd+f 

1ense sand or

OC cla*

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C% tests Ho0 to deterine strength "araeters c and φ

   1  e  &   i  a   t  o  r  s   t  r  e  s  s ,

    ∆   σ   d

 A'ial strain

   S   h  e  a  r  s   t  r  e  s  s ,

   τ

   σor   σ9

(∆σd+f(

Confining stress 5 σ3(

σ3( σ4(σ3a σ4a

)∆σd+fa

φcuMohr ; Coulo( failureen&elo"e in ters of

total stresses

ccu

σ4 5 σ3 7 )∆σd+f  

σ3

Total stresses at failure

(∆σd+fa

Confining stress 5 σ3a

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)∆σd+fa

C% tests Ho0 to deterine strength "araeters c and φ

   S

   h  e  a  r  s   t  r  e  s  s ,

   τ

   σor   σ9σ3( σ4(σ3a σ4a

)∆σd+fa

φcuMohr ; Coulo( failureen&elo"e in ters of

total stresses

ccuσ93( σ94(

σ93a σ94a

Mohr ; Coulo( failure

en&elo"e in ters of

effecti&e stresses

φ9

C9 ufa

uf(

σ94 5 σ3 7 )∆σd+f  uf  

σ93 5 σ3  uf  

/ffecti&e stresses at failure

uf 

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C% tests

Strength "araeters c and φ o(tained fro C1 tests

Shear strength

"araeters in ters of

total stresses are ccu and

φcu

Shear strength"araeters in ters of

effecti&e stresses are c9 

and φ9

c9 5 cd and φ9 5 φd

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C% tests $ailure en&elo"es

$or sand and NC Cla*, ccu and c9 5

Therefore, one C% test 0ould (e sufficient to deterine φcu 

and φ9(5 φd+ of sand or NC cla*

   S   h  e  a  r  s   t  r  e  s  s ,

   τ

   σor   σ9

φcuMohr ; Coulo( failureen&elo"e in ters oftotal stresses

σ3a σ4a)∆σd+fa

σ3a σ4a

φ9

Mohr ; Coulo( failureen&elo"e in ters of

effecti&e stresses

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Soe "ractical a""lications of C% anal*sis for

cla*s

τ τ 5 in situ undrainedshear strength

Soft cla*

4. /(an!ent constructed ra"idl* o&er a soft cla* de"osit

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Soe "ractical a""lications of C% anal*sis for

cla*s

2. @a"id dra0do0n (ehind an earth da

τ 5 %ndrained shear strengthof cla* core

Coreτ

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Soe "ractical a""lications of C% anal*sis for

cla*s

3. @a"id construction of an e(an!ent on a natural slo"e

Note: Total stress "araeters fro C% test )ccu and φcu+ can (e used for sta(ilit*"ro(les 0here,

Soil ha&e (ecoe full* consolidated and are at e6uili(riu 0ith the

e'isting stress state Then for soe reason additional stresses are

a""lied 6uic!l* 0ith no drainage occurring

τ 5 n situ undrained shear strength

τ

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Unconsolidated- Undrained test (UU Test)

1ata anal*sis

σC 5 σ3

σC 5 σ3No

drainage

nitial s"ecien condition

σ3 7 ∆σd

σ3

No

drainage

S"ecien condition

during shearing

nitial &olue of the sa"le 5 A B H

8olue of the sa"le during shearing 5 A B H

Since the test is conducted under undrained condition,

 A B H 5 A B H

 A B)H ; ∆H+ 5 A B H

 A B)4 

 ; ∆H?H

+ 5 A

  z 

 A A

ε −=

1

0

U lid t d U d i d t t (UU T t)

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Unconsolidated- Undrained test (UU Test)

Ste" 4: ediatel* after sa"ling

5 7

Ste" 2: After a""lication of h*drostatic cell "ressure

∆uc 5 - ∆σ3

σC 5 σ3

σC 5 σ3 ∆uc

σ93 5 σ3  ∆uc

σ93 5 σ3  ∆uc

No

drainage

ncrease of "0" due to

increase of cell "ressure

ncrease of cell "ressure

S!e"ton9s "ore 0ater

"ressure "araeter, -

Note: f soil is full* saturated, then - 5 4 )hence, ∆uc

 5 ∆σ3

+

U lid t d U d i d t t (UU T t)

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Unconsolidated- Undrained test (UU Test)

Ste" 3: 1uring a""lication of a'ial load

σ3 7 ∆σd

σ3

No

drainage

σ94 5 σ3 7 ∆σd  ; )∆uc > ∆ud +

σ93 5 σ3 ; )∆uc > ∆ud+ 

∆ud 5  A-∆σd

∆uc >  ∆ud

5 7

ncrease of "0" due to increase

of de&iator stress

ncrease of de&iator stress

S!e"ton9s "ore 0ater

"ressure "araeter, A

U lid t d U d i d t t (UU T t)

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Unconsolidated- Undrained test (UU Test)

Co(ining ste"s 2 and 3,

∆uc 5 - ∆σ3 ∆ud 5  A-∆σd

∆u 5 ∆uc 7 ∆ud

Total "ore 0ater "ressure increent at an* stage, ∆u

∆u 5 - ∆σ3 7 A∆σdDS!e"ton9s "ore

0ater "ressure

e6uation∆u 5 - ∆σ3 7 A)∆σ4 ; ∆σ3D

U lid t d U d i d t t (UU T t)

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Unconsolidated- Undrained test (UU Test)

Ste" 4: ediatel* after sa"ling

Total, σ 5 Neutral, u /ffecti&e, σ97

ur 

Ste" 2: After a""lication of h*drostatic cell "ressure

σ98 5 ur 

σ9h 5 ur 

σC

σCu

r 

 + ∆uc

5 ur 

 + σc

)Sr  5 4E  - 5 4+

Ste" 3: 1uring a""lication of a'ial load

σC 7 ∆σ

σC

No

drainage

No

drainageur  + σc > ∆u

σ98C 5 σC 7 ur   σC 5 ur 

σ9h 5 ur 

Ste" 3: At failure

σ98 5 σC 7 ∆σ 7 ur σc  ∆u

σ9h 5 σC 7 ur σc  ∆u

σ9hf  5 σC 7 ur σc  ∆uf 5

σ93f  

σ98f  5 σC 7 ∆σf  7 ur σc  ∆uf  5 σ94f  

ur  + σc > ∆uf 

σC

σC 7 ∆σf Nodrainage

Unconsolidated Undrained test (UU Test)

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Unconsolidated- Undrained test (UU Test)

Total, σ 5 Neutral, u /ffecti&e, σ97Ste" 3: At failure

σ9hf  5 σC 7 ur σc  ∆uf 5σ93f  

σ98f  5 σC 7 ∆σf  7 ur σc  ∆uf  5 σ94f  

ur  + σc > ∆uf 

σCσC 7 ∆σf No

drainage

Mohr circle in ters of effecti&e stresses do not de"end on the cell "ressure.

Therefore, 0e get onl* one Mohr circle in ters of effecti&e stress for different

cell "ressures

τ

σ9σ9

3

σ94∆σf 

Unconsolidated Undrained test (UU Test)

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σ3(

σ4(σ3a

σ4a∆σf 

σ93

σ94

Unconsolidated- Undrained test (UU Test)

Total, σ 5 Neutral, u /ffecti&e, σ97Ste" 3: At failure

σ9hf  5 σC 7 ur σc  ∆uf 5σ93f  

σ98f  5 σC 7 ∆σf  7 ur σc  ∆uf  5 σ94f  

ur  + σc > ∆uf 

σCσC 7 ∆σf No

drainage

τ

σ or σ9

Mohr circles in ters of total stresses

uau(

$ailure en&elo"e, φu 5

cu

Unconsolidated Undrained test (UU Test)

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σ3( σ1(

Unconsolidated- Undrained test (UU Test)

/ffect of degree of saturation on failure en&elo"e

σ3a σ1aσ3c σ1c

τ

σ or σ9

S F 4E S G 4E

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Soe "ractical a""lications of %% anal*sis for

cla*s

τ τ 5 in situ undrainedshear strength

Soft cla*

4. /(an!ent constructed ra"idl* o&er a soft cla* de"osit

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Soe "ractical a""lications of %% anal*sis for

cla*s

2.

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Soe "ractical a""lications of %% anal*sis for

cla*s

3. $ooting "laced ra"idl* on cla* de"osit

τ 5 n situ undrained shear strength

Note: %% test siulates the short ter condition in the field.

Thus, cu  can (e used to anal*e the short ter

(eha&ior of soils

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/'a"le

I Ji&en

 ; Tria'ial co"ression tests on three s"eciens of a soil sa"le

0ere "erfored. /ach test 0as carried out until the s"ecien

e'"erienced shear failure. The test data are ta(ulated as follo0s:

I @e6uired

 ; The soil9s cohesion and angle of internal friction

S"ecien

Nu(er 

Minor Princi"al Stress

)!i"s?ft2+

1e&iator Stress at $ailure

)!i"s?ft2+

4 4.KK L.

2 2. .L

3 K.32 .L

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/'a"le

S"ecien

Nu(er 

Minor Princi"alStress

)!i"s?ft2+

1e&iator Stressat $ailure

)!i"s?ft2+

Major Princi"al

Stress )!i"s?ft2

+

4 4.KK L. .2

2 2. .L .3

3 K.32 .L 44.2

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/'a"le

2 K 4 42 4K

2

K

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/'a"le

2 K 4 42 4K

2

K

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/'a"le

2 K 4 42 4K

2

K

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/'a"le

2 K 4 42 4K

2

K

K

2

2

1

/9.0

26

4

2tan

4

2tan

 ft kipc ==

   

  =

=

−

φ 

φ 

φ 

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TH/ /N1