$5\mathrm{.}0(30$ marks$)$

Foundation engineers are often challenged by the existence of soft compressiblesoils at the construction site. Figure $4\mathrm{.}0$ shows a soil profile with a silty sand $=17k\frac{N}{m^3}$;${}_{\text{s}\text{a}\text{t}}=19\mathrm{.}2k\frac{N}{m^3})$ underlain by high plasticity clay $(($:${}_{\text{s}\text{a}\text{t}}=18\mathrm{.}8k\frac{N}{m^3}$