Problem $4(15\%)$:

For a dry sand specimen in a direct shear test box, the following are given:

Angle of friction: ${}^{\text{'}}=33$

Size of specimen: $2$ inch $2$ inch $1\mathrm{.}2$ inch $($height$)$

Normal stress: $30l\frac{b}{?}$ inch ${?}^2$

Part a $(10\%)$ : Determine the shear stress $(l\frac{b}{i}{n}^2)$ required to cause failure.

Part b $(5\%)$ : Determine the shear force $T(lb)$ required to cause failure.