Analysis of Pile-Raft Foundations with 3D Finite-Element Method

One of the most challenging problems in soil-structure interaction is the piled raft. Piled-raft foundations for important high-rise buildings have proved to be a viable alternative to conventional pile foundations or mat foundations. The concept of using piled raft foundation is that the combined foundation is able to support the applied axial loading with an appropriate factor of safety and that the settlement of the combined foundation at working load is tolerable. In some instances the piles are spaced uniformly and in other cases are spaced strategically to achieve a more uniform settlement of the mat. Two strong reasons dictate the use of the 3D Finite Element Method (FEM): (1) the problem is so complex that simplified methods cannot model the problem correctly; and (2) codes for the FEM are available, powerful, and capable of being run on the personal computer. Thus, the modeling of the raft, piles, and supporting soil as a soil-structure-interaction problem using FEM is a feasible method. Two piled-raft foundations were analyzed using the FEM program. Comparisons were made between experimental and analytical results and the FEM was shown to yield excellent results for the cases analyzed.