ANALYSIS OF THICK-RAFT FOOTINGS BY BEM AND LAYER-WISE SUMMATION METHOD

Thick-raft footings are common type of building foundations. They can be analyzed by boundary element or finite element method on the base of elastic foundation soil model, but the elastic foundation soilmodel cannot represent the real behavior of foundation soil and finite element method needs to define a lot of soil elements. The authors propose a way to analyze thick-raft footings by nonsingular boundary element method(BEM)and layer-wise summation method in this paper. Nonsingular BEM is utilized to calculate the deformation of the raft footing and ground reaction on it at first with an initial elastic coefficient of foundation soil. Layer-wise summation method, in which the action on the ground is equal to the balance pressure of the ground reaction, ithen adopted to estimate the foundation soil settlement. The settlement is used to modify the initial elasticcoefficient of foundation soil. Then the new deformation of the raft footing and ground reaction on it acalculated by non-singular BEM again. Consequently, a new settlement would be also estimated by the layer-wise summation method. This iterative process continues until a reasonable result is obtained. The proposed strategy is easy for programming and applicable to footings with different forms and boundary conditions. Two examples are provided to verify the present method.