3. (a) A soil profile consists of two layers: a layer of silty sand 6 m

deep, underlain by a 5 m layer of saturated clay. The properties

of the two layers are:

Layer I (silty sand):

Saturated unit weight ysat = 19 kN/m³.

Layer II (clay):

Saturated unit weight ysat=18 kN/m³

Determine and plot the pore pressure and the total and effective

stresses at z=0 m, z=2 m, z=6 m and z=11 m depth for the

following two cases:

(i) the water table is at the ground surface

marks)

(ii) the water table is at 2 m below ground surface but the silty

sand is saturated with capillary water to a height up to the

ground surface.

(6

marks)

(6

(b) A uniformly distributed load of 60 kN/m² is applied to a 3m

deep layer of clay. The clay is free to drain at both the top and

the bottom. The coefficient of volume compressibility m, of

the clay is 0.2 m²/MN. The coefficient of permeability of the

clay is 2x10-¹0 m/s.

i) calculate the coefficient of consolidation of the clay layer

(2 marks)

ii) calculate the final settlement of the clay layer

marks)

(2/niii) calculate the settlement of the clay when the degree of

consolidation is 90%

(2

marks)

iv) calculate the time when the settlement is 20% of the final

settlement

(2

marks)

Take the unit weight of water Y'w = 10 kN/m³

Total 20 marks