Question

A smooth rigid retaining wall moves as shown in the sketch causing the backfill material to fail. The backfill material is homogeneous and isotropic, and obeys the Mohr- Coulomb failure criteria . The major principal stress is

• A. Parallel to the wall face and acting downwards
• B. normal to the wall face
• C. oblique to the wall face acting downwards
• D. oblique to the wall face acting upwards

Answer 1

The correct option is B normal to the wall face

Smooth rigid wall moves towards the backfill till backfill material fails so passive earth pressure will act on the wall. Passive earth pressure, ${\sigma }_3={\sigma }_1{K}_p$

Where major principal stress is ${\sigma }_3$ which is acting normal to the wall face (because top surface of backfill is horizontal)