Raft Foundation Design Practices

Abstract

In the recent years, there has been signi cant increase in high rise buildings due to lack of space and requirement of amenities at a particular place. This has necessiated the use of raft foundation. The use of raft foundation tends to reduce the chances of di erential settlement and allow increased pressure at foundation level to be trans- mitted with the concept of Buoyancy Raft. In conventional analysis & design of raft foundation through case studies it has been found that the e ect of soil which supports the structure is generally neglected. Ac- tually behavior of structure depends on soil strata. The design of raft foundation is a soil structure interaction problem. SSI e ect de- pends on many factors like Superstructure sti ness, Loadings, Footing sti ness, Raft Rigidity. The S.S.I has less in uence on low rise buildings. An attempt has been made to understand the behavior of building (5-storey) un- der the e ect of Soil Structure Interaction. The various methods suggested by I.S code and A.C.I code has been considered. Winkler method and Elastic Half Space approach has also been considered for the study of SSI e ect with three type of soils having di erent modulus of elasticity of raft. After detail design to decide thickness of raft and reinforcement provided, the cost analysis has been carried out for com- parisons of di erent approaches of raft foundation design. It has been found that rigid method tends to give higher moments, so overall rigid method is costlier than compared to other methods.