Shear Strength of Soil Soil Shear Strength Soil

Shear Strength of Soil

Soil Shear Strength Soil in weak in shear To determine the shear strength of soil Mohr-Coulomb Yield Criterion is used t t = c + sn tan f Soil Cohesion Angle of Friction Yield Surface s t=c+ n tan f f c sn Determination of soil strength parameters ( c and f ) in the lab 1 - Direct Shear Test 2 - Unconfined Compression Test 3 - Triaxial Compression Test

Direct Shear Test Normal Force N Shearing Force T t = T/A D = Horizontal Displacement s = N/A T Failure D

Direct Shear Test t t s 1 t s 2 t Failure D s 3 D D Test # 1 2 3 Normal Stress (sn) √ √ √ Shear at Failure (t) √ √ √ t s t= c + n c t 1 s 1 f tan f t 2 s 2 t 3 sn

Unconfined Compression Test Deviator Stress Ds Ds Failure e t t= cu Cu = qu/2 s 1 qu = Unconfined compressive strength Cu = Unconfined shear strength qu = s 1 sn

TRIAXIAL COMPRESSION TEST Failure Surface By Kamal Tawfiq, Ph. D. , P. E.

Triaxial Compression Test Deviator Stress 1 - Consolidated Undrained Test (CU) Step 1 Ds s 2 Step 2 Ds Failure e t s 1 = Ds + s 2 Confining Pressure Ds Ds s 2 s 2 s 2 + t= c s 2 cu s 2 Ds s 2 s 1 - s 2 fu nf s n ta s 1 - s 2 s 1 sn

Triaxial Compression Test 2 - Consolidated Drained Test (CD) Deviator Stress Ds Step 1 s 2 Step 2 Ds Failure e s 1 = Ds + s 2 Confining Pressure s 2 s 2 s 2 t Ds s 2 Ds + t= c cd s 2 s 1 - s 2 fd nf s n ta s 1 - s 2 s 1 sn

Triaxial Compression Test 3 - Unconsolidated Undrained Test (UU) Deviator Stress Ds Step 1 s 2 Step 2 Ds Failure e t s 1 = Ds + s 2 Confining Pressure s 2 Ds s 2 t= c s 2 s 2 Ds cu s 2 s 1 - s 2 s 1 sn

Triaxial Compression Test 1 - Applying Confining Stresses 2 - Loading )F F 2 Each Circle = One Test F 2 F 2 + F 2 3 - At Failure Axial = F 1 stress Deviator stress = )Ff F 2 J F 2 2 F 2 + F 1 = Major Principle Stress F 2 = Minor Prencipal Stress + Confining stress = F 2 Failure Surface + )F )F= deviator stress )Ff = F 1 Failure Surface Cohesion = c F 2 2 F 2 F 1 F 1 Fn By Kamal Tawfiq, Ph. D. , P. E.