Piled Raft and Compensated Piled Raft Foundations for Soft Soil Sites: Fid-Bau Portal

Piled Raft and Compensated Piled Raft Foundations for Soft Soil Sites

Poulos, Harry G.

This paper re-visits the compensated piled raft foundation system, and outlines a simplified approach to the analysis of both conventional piled rafts and compensated piled raft foundations for the support of structures on very soft clays. Two cases are considered: the first where only applied load acts on the foundation, and the second where both applied load and externally imposed ground settlements act. It is demonstrated that the use of compensation, via excavation of the soil and embedment of the raft, can lead to significant reductions in settlement compared to normal (uncompensated) piled rafts. Importantly, when ground settlements occur, the use of compensated piled rafts can lead to significantly reduced differential settlements between the structure and the ground, compared to the case where the structure is supported by end bearing piles. Indeed, the latter may be counter-productive and lead to the not uncommon situation where the building stands well above the surrounding ground. A simplified design approach is proposed, and it is demonstrated that this simplified approach can lead to a computed behavior which is consistent with past experience in Mexico City.