Question

Due to capillary rise in soil, the effective stress ...........

• A. decreases
• B. does not change
• C. increases
• D. becomes infinity

Hint:

Remember: Capillary water creates suction, which increases the effective stress — this is crucial for understanding shear strength in unsaturated soils.

Answer 1

The Correct Option is C

Capillary rise occurs when water moves upward through the soil pores above the groundwater table due to surface tension.
This results in the development of negative pore water pressure (also known as suction) in the capillary zone.
The effective stress ($\sigma'$) in soil is calculated as:
\[ \sigma' = \sigma - u \]
Where:
$\sigma$ = total stress
$u$ = pore water pressure
In the case of capillary rise, the pore water pressure $u$ becomes negative.
So, subtracting a negative value (i.e., $-u$) leads to an increase in effective stress.
Hence, capillary action causes the soil particles to be held together more tightly, increasing the effective stress.