Problem $4$: A vertical retaining wall $25ft$ high supports a deposit of sand having a level backfill.

Soil properties are as follows: $=115$ pcf and $=32.$ Using Rankine theory, calculate the $($a$)$ total

active earth pressure $($psf$)($b$)$ total active earth force $($plf$)$per foot of wall and $($c$)$ location $($ft$)$ of the

resultant force from the base of the wall.