Question

Study the statements listed below

(1) Negative skin friction is developed when the pile is driven through a recently deposited clay layer

(2) Negative skin friction is developed when the pile is driven through a layer of dense sand

(3) Negative skin friction is developed due to sudden drawdown of the water table

Out of these statements

1. 1 alone is correct
2. 2 alone is correct
3. 2 and 3 are correct
4. 1 and 3 are correct

Answer 1

Correct Answer - Option 4 : 1 and 3 are correct

Concept:

Negative skin friction is a downward drag acting on a pile due to downward movement of surrounding compressible soil relative to pile.

Negative friction also occurs when settlement of surrounding soil is more than that of pile.

Negative skin friction reduces the load-carrying capacity of the pile.

Negative skin friction may develop under following conditions

• It happens when the surrounding soil has been recently filled or formed. As the soil consolidates the earth fill moves downward developing friction forces on the perimeter on the perimeter of pile which tends to carry pile further into ground.
• Negative skin friction may develop due to lowering of water table. When water table is lowered the effective pressure increases causing consolidation of soil, with the resultant settlement and friction force being developed on the pile.