Abstract: The ground bearing capacity of thin layer soil under raft foundation is different from that of uniform ground, and cannot be simply determined by using the usual natural ground bearing capacity method. This article determines the strength index and deformation parameters of the thin layer soil ground through field plate loading tests, and divides the raft foundation into several grids to calculate the foundation stiffness of each grid employing the tangent modulus layerwise summation method. The raft foundation is considered as an elastic foundation plate supported by each grid, and the compressive stress at the bottom of the plate under the joint action of each grid is calculated. The compressive stress of each grid is compared with the ultimate ground bearing capacity predicted using thin layer soil ground strength parameters to judge the safety of the ground bearing capacity, and then according the settlement deformation of the raft, the allowable bearing capacity of this thin layer soil ground is determined by the strength bearing capacity of the thin layer soil ground and the deformation control of the raft foundation. Compared with the finite element method, it has been proven that this is a more suitable method for determining the ground bearing capacity of the thin layer soil under the raft foundation.

Key words: raft foundation, tangent modulus method, ground bearing capacity, thin layer soil, pressure plate load test