The figure shows an element of soil at the interface between two dry sand layers on a 28 slope. The interface is 10 ft below

The figure shows an element of soil at the interface between two dry sand layers on a 28° slope. The interface is 10 ft below the ground surface, and for both sand layers the friction angle is 34° and Ko = 0.44. Assume that the shear stress is zero on both the vertical and horizontal planes.

(a) Draw the Mohr circle for this point, and determine the pole location.

(b) Determine the normal and shear stresses on the soil interface (i.e., on the 28° plane).

(c) What is the shear stress on the failure plane (T f) and what is the shear stress on the failure plane at failure (T ff)? Use these values to determine the factor of safety.

Dry sand Yd= 112 pcf 28 10 Dry sand Yd 105 pcf