A retaining wall $4$ m high is shown below. The unit weight of the backfill material is $19k\frac{N}{m^3}.$ The

friction angle is $25.$ The coefficient of concrete friction with soil is $0\mathrm{.}45.$ The unit weight of concrete is

$24k\frac{N}{m^3}.$

a$.$ Draw the variation of Rankine's active earth pressure on the wall with depth.

b$.$ The factor of safety against sliding.

c$.$ The factor of safety against overturning.