Skin friction is a very important factor in civil engineering construction. In so many mega-structures, skin friction concept is used including the great “Burj-Al-Arab” to solve the impediments imposed during the construction. But negative skin friction is a factor we should always aware of. It can cause serious damage to the structure because of improper knowledge.
Negative Skin Friction in Piles
When the soil layer surrounding a portion of the pile shaft settles more than the pile, a downward drag occurs on the pile. The drag is known as negative skin friction. It occurs in the soil zone which moves downward relative to the pile. The negative friction imposes an extra downward load on the pile. So, clay will settle downward and relative pile settle upward.
How To Solve Negative Skin Friction
Negative skin friction can be eliminated by providing protective sleeve or a coating on the section surrounds the settling soil.
Qu = Skin friction (Qs) + End bearing (Qp)
Q = Qs + Qp
For negative skin friction,
Q = – Qs + 0 (End bearing = 0)
so, Q = – Qs