Question

Which of the following statements is/are INCORRECT?
 

• A. As the depth of the ground water table from the ground surface increases, the effective stress in the soil decreases.
• B. Bulking of the moist sand is due to the capillary action in the sand.
• C. The effective stress in a liquefied soil is almost zero.
• D. The earth pressure at any point in the soil, under all conditions, is always smaller than the vertical effective stress at that point.

Hint:

Effective stress increases as the water table depth increases. Earth pressure can vary with stress condition; don’t assume it's always less than vertical stress.

Answer 1

The Correct Option is A, D

Option (A):
Incorrect. As the water table goes deeper (i.e., increases in depth from the surface), the pore water pressure acting at a point in the soil decreases. Hence, the effective stress \((\sigma' = \sigma - u)\) increases, not decreases.
Option (B):
Correct. Bulking of sand occurs due to moisture forming meniscus at particle contacts, leading to capillary tension and apparent volume increase.
Option (C):
Correct. In liquefied soils, the pore water pressure equals the total stress, leading to near-zero effective stress.
Option (D):
Incorrect. Earth pressure can be greater, equal, or less than vertical effective stress depending on the stress state (active, passive, or at-rest). Therefore, the statement is not always true.