ANS:B - minor principal stress is vertical

Deposit variability:

Because of variations in soil types, gradations, particle arrangements, and dry density values, the effective friction angle is rarely uniform with depth. It takes considerable judgment and experience in selecting an effective friction angle. In passive earth pressure, two sets of failure planes are formed each inclined at an angle (45 ÷ 2) to the horizontal plane which is the direction of minor principle plane, as we know minor principle stress acts on minor principle plane so minor principle plane is in a vertical direction.