Question

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?

• A. 1, 2 and 3
• B. 1 and 2 only
• C. 2 and 3 only
• D. 1 and 3 only

Answer 1

The correct option is D 1 and 3 only

When water level fluctuation takes place above a lake, total stress $\left(\sigma \right)$ and pore water pressure (u) changes with same value in a sand layer below a lake, hence effective stress does not change. But when the WT is below the ground level, any rise or fall in the WT causes different and unequal changes in both $\sigma$ & u.
Capillary saturation leads to development of negative pore pressure (i.e. -u)

Effective stresses, $\overline{\sigma }=\sigma -(-u)=\sigma +u$

$\therefore$ Increment is observed in $\sigma$.