Thickness-Rigidity Relationship of Mat or Raft Foundation

In the previous post we tried to find answer of different query about mat foundation. Here we will try to make relation between mat thickness and its rigidity. In normal condition an uniformly thickened mat foundations are common. But foundation engineer may change thickness to have economy of construction.

The thickened portion of mat is located below columns as it provides maximum economy. Case studies of many mat foundations show that a reduction in thickness of 40% can be allowed away from individual column faces. 

But in this purpose with variable thickness and applying all factors, its effects on mat rigidity have to be investigated carefully. Though the impacts of thickness were found little on maximum settlement or load sharing, it affects bending moments and differential settlement. The thickening of raft up to certain limit renders a greater bending capacity. But above 1.5m thickness a little effect on maximum bending capacity are observed.

It is found that negative bending moment is reduced with increment of raft thickness whereas it simultaneously produces a increased positive bending moment.