Correct option is B
When the soil surrounding a pile settles at a greater rate than the pile itself, it creates a downward drag force on the pile. This phenomenon is referred to as
negative skin friction. It occurs because of consolidation of the soil or due to fill being placed over soft compressible soil layers.
The downward drag induced by negative skin friction reduces the effective load-carrying capacity of the pile, as the pile needs to bear not only the structural load but also the additional drag from the soil movement. This drag force acts along the shaft of the pile and can result in structural stress on the pile.
This negative skin friction typically occurs in soft clays or loose soils, especially when there is settlement due to consolidation or placement of additional loads on the soil surface. Proper design considerations are necessary to mitigate this effect and ensure the stability of the pile foundation system.
