AN ANALYTICAL MODEL TO ESTIMATE LOAD CAPACITY POSSESSED BY SUPPORTING SOIL FOR PILED RAFT FOUNDATIONS

While piled raft foundations are widely adopted in the construction of tall or multistory buildings, an accurate estimation and control of load capacity possessed by supporting soil become essential for the safety of buildings and construction cost reduction, especially in the case on soft soil subgrades. This paper presents an effective analytical model to estimate load capacity possessed by supporting soil for piled raft foundations. In this approach the bending plate is approximately assumed to have linear elastic properties and is modeled by the generalized conforming finite element method while the supporting soil subgrade is modeled by the finite layer method(FLM). Each pile is represented by a single element, and its nonlinear stiffness is evaluated through a load vs. pile head displacement curve obtained from static loading tests, resulting in the governing system of equations for plate-pile-soil interaction problems. The FLM is not only capable of representing the layered subgrade behavior, but it is also of low computation cost. Several real piled raft foundations on the soft soil subgrade have been analysed. The numerical results indicate that, in general, for tall buildings, the load capacities possessed by supporting soil are about 8~15% of the whole one; and that for multistory buildings, where the piles are often used to prevent excessive settlements, are often more than 25%. It can be seen from the numerical results that the load capacity possessed by supporting soil is more affected by stiffness of piles, and increases with the settling of the building, its full utilization in design would evidently reduce the cost of a piled raft foundation construction.