GATE Civil Engineering (CE) 2018 Shift 1 Solved Paper

A rigid smooth retaining wall of height $7\mathit{m}$ with vertical backface retains saturated clay as backfill. The saturated unit weight and undrained cohesion of the backfill are $17.2\mathit{k}\mathit{N}∕{\mathit{m}}^3$ and $20\mathit{k}\mathit{P}\mathit{a}$, respectively. The difference in the active lateral forces on the wall (in $\mathit{k}\mathit{N}$ per meter length of wall, up to decimal places), before and after the occurrence of tension cracks is_______