Question

For the soil strata shown in figure, the water table is lowered by drainage by 2 m and if the top 2 m thick silty sand stratum remains saturated by capillary action even after lowering of water table, the increase in effective vertical pressure in kPa at mid-height of clay layer will be

• A. 0.2
• B. 2
• C. 20
• D. 200

Answer 1

The correct option is C 20

Effective stress = Total stress - Pore water pressure

After lowering of water table, soil above water table still remains saturated so total stress will not change. Water table lowers by 2m

So decreases in pore water pressure,

= 2${\gamma }_w$

= 20kN/$m^2$

Hence effective stress increases by 20 kN/$m^2$