Triaxial test question

[ketanco]

Triaxial test for saturated cohesionless soil

Max vertical load - 121 lb

sample diameter 3 in

chamber pressure 16.4 psi

pore water pressure 10 psi

for drained conditions, what is the effective friction angle?

can someone solve and explain. can not understand the solution either...

right answer is 35 degrees

 

[civilized_naah]

Added axial load = 121 lb

Added axial stress = 17.12 psi

Total axial stress = 17.12 + 16.4 = 33.52 psi (sigma_1)

Effective axial stress = 33.52-10 = 23.52 psi(sigma_1_prime)

Total radial stress = 16.4 psi (sigma_3)

Effective radial stress = 16.4-10 = 6.4 psi(sigma_3_prime)

Friction angle phi is found from:

sin phi = ( sigma_1_prime - sigma_3_prime) / (sigma_1_prime + sigma_3_prime)

sin phi = ( 23.52 - 6.4) / (23.52 + 6.4) = 0.572

phi = 34.9 deg