Example $13\mathrm{.}5$: A smooth backed vertical wall is $6\mathrm{.}3$ m high and retains a soil with a bulk unit

weight of $18k\frac{N}{m^3}$ and $=18.$ The top of the soil is level with the top of the wall and is

horizontal. If the soil surface carries a uniformly distributed load of $4\mathrm{.}5k\frac{N}{m^2},$ determine the

total active thrust on the wall per lineal metre of the wall and its point of application.