Changes in Effective Stress

Q. Consider the following statements:
1. Effective stress in a sand layer below a lake with standing water does not alter as the water level fluctuates.
2. Regarding water table below the ground surface, any rise in the water table causes equal changes in both pore pressure and effective stress.
3. Capillary saturation will cause the effective stress in increase.
Which of the above statements are correct?

1. 1, 2 and 3
2. 1 and 2 only
3. 2 and 3 only
4. 1 and 3 only

Q. At a site where sand deposit extends to a great depth, the ground water table is lowered from 2 m below G.L to 3 m below the G.L. The increase in effective stress is
$({\gamma }_d=16kN/m^{3}and{\gamma }^{\prime }=10kN/m^3)$

1. $16kN/m^2$
2. $10kN/m^2$
3. $26kN/m^2$
4. $6kN/m^2$

Q. In a deposit of silt, the water table originally at a depth of 1 m below ground level was lowered to 3 m below ground level and got capillary saturated. The saturated unit weight of soil is $20kN/m^3.$ The change in effective pressure at a depth of 2 m is $(Assume{\gamma }_w=10kN/m^3)$

1. $10kN/m^2$
2. $20kN/m^2$
3. $30kN/m^2$
4. $10kN/m^2$

Q. Assuming that a river bed level does not change and the depth of water in river was 10m, 15 m and 8m during the months of February, July and December respectively of a particular year. The average bulk density of the soil is $20kN/m^3$. The density of water is $10kN/m^3$. The effective stress at a depth of 10 m below the river bed during these months would be

1. $300kN/m^{2}inFebruary$ , $350kN/m^{2}inJulyand$ , $320kN/m^{2}inDecember$
2. $100kN/m^{2}inFebruary$ , $100kN/m^{2}inJulyand$ , $100kN/m^{2}inDecember$
3. $200kN/m^{2}inFebruary$, $250kN/m^{2}inJulyand$, $180kN/m^{2}inDecember$
4. $300kN/m^{2}inFebruary$ , $350kN/m^{2}inJulyand$ , $280kN/m^{2}inDecember$