Consider the planar block slide in the sketch. 

(a) Show algebraically that reduction of the slide mass volume from V_o to V₁ by excavating a relieving bench near the crest necessarily increases the safety factor, provided the water table is lowered below the toe. 

(b) Show that placing a berm of weight W₁ at the toe of the slide, where cohesion c₁ and friction angle φ₁ are mobilized at the berm bottom, necessarily increases the safety factor, other factors remaining the same.

he VI hw WT , wi