Shear Strength of Soil
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Shear Strength of Soil By Kamal Tawfiq Fall 2007. t. f. t = c + s n tan f. c. s n. Soil Shear Strength Soil in weak in shear To determine the shear strength of soil Mohr-Coulomb Yield Criterion is used t = c + s n tan f. Yield Surface. Angle of Friction. Soil Cohesion.

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Shear Strength of Soil By Kamal Tawfiq Fall 2007

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Shear strength of soil by kamal tawfiq fall 2007

Shear Strength of Soil

By

Kamal Tawfiq

Fall 2007


Shear strength of soil by kamal tawfiq fall 2007

t

f

t = c + sntan f

c

sn

Soil Shear Strength

Soil in weak in shear

To determine the shear strength of soil Mohr-Coulomb Yield Criterion is used

t = c + sn tan f

Yield Surface

Angle of Friction

Soil Cohesion

Determination of soil strength parameters ( c and f ) in the lab

1- Direct Shear Test

2- Unconfined Compression Test

3- Triaxial Compression Test


Shear strength of soil by kamal tawfiq fall 2007

Direct Shear Test

Normal Force

N

t = T/A

s = N/A

Shearing Force

D = Horizontal Displacement

T

T Failure

D


Shear strength of soil by kamal tawfiq fall 2007

Test #Normal Stress (sn)Shear at Failure (t)

1√ √

2√ √

3√ √

Direct Shear Test

t

t

t

s3

s2

s1

t Failure

t Failure

t Failure

D

D

D

t

f

t= c + sntan f

t3

t2

t1

c

sn

s3

s1

s2


Shear strength of soil by kamal tawfiq fall 2007

Unconfined Compression Test

Deviator Stress

Ds

Ds Failure

e

t

t= cu

Cu = qu/2

s1

sn

qu = s1

qu = Unconfined compressive strength

Cu = Unconfined shear strength


Shear strength of soil by kamal tawfiq fall 2007

TRIAXIAL COMPRESSION TEST

Failure Surface

By Kamal Tawfiq, Ph.D., P.E.


Shear strength of soil by kamal tawfiq fall 2007

Triaxial Compression Test

Deviator Stress

1- Consolidated Undrained Test (CU)

Ds

s2

Step 1

Step 2

Ds Failure

e

t

s1 = Ds + s2

Confining

Pressure

Ds

Ds

fu

t= c + sntan f

s2

s2

cu

s2

s2

s2

s2

s2

s2

s2

s2

s1

s2

s2

s2

s1

s1

sn

s1 - s2

s2

s2

s1 - s2

Ds


Shear strength of soil by kamal tawfiq fall 2007

Triaxial Compression Test

2- Consolidated Drained Test (CD)

Deviator Stress

Ds

s2

Step 1

Step 2

Ds Failure

e

s1 = Ds + s2

Confining

Pressure

t

Ds

s2

s2

fd

s2

s2

t= c + sntan f

s2

cd

s2

s2

s2

s1

s2

s1

s1

s2

sn

Ds

s1 - s2

s1 - s2


Shear strength of soil by kamal tawfiq fall 2007

Triaxial Compression Test

3- Unconsolidated Undrained Test (UU)

Deviator Stress

Ds

s2

Step 1

Step 2

Ds Failure

e

t

s1 = Ds + s2

Confining

Pressure

Ds

t= c

s2

s2

cu

s2

s2

s2

s2

s1

s1

s2

s1

s2

sn

s1 - s2

s2

s2

s1 - s2

Ds


Shear strength of soil by kamal tawfiq fall 2007

1- Applying

2- Loading

3- At Failure

Confining

Stresses

Axial

F

=

1

stress

F

F

)

Deviator stress

=

)

f

+

+

F

F

F

Confining stress

=

2

2

2

F

F

F

F

F

F

2

2

2

2

2

2

2

F

F

F

Failure

2

2

2

Surface

+

+

F

F

)

)

f

F

= Major

Principle Stress

F

=

1

1

F

= Minor Prencipal Stress

)F

= deviator stress

2

Triaxial Compression Test

Each Circle

=

One Test

J

Failure Surface

c

Cohesion =

2

F

F

F

F

F

F

F

2

2

1

1

1

2

n

By Kamal Tawfiq, Ph.D., P.E.


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