Numerical analysis of interaction of superstructure-piled raft foundation-the foundation soil and optimal design for variable stiffness of the pile raft foundation

In this paper, finite element method was used to study the interaction and common effect among superstructure-piled raft foundationfoundation interaction. The research results show that when the interaction of superstructure-the pile raft foundation-foundation and the influence among them occur, the foundation settlement of overall and differential subsidence with the increase of the floor change nonlinearly, the upper structure existing in secondary stress and the bending moment and axial force are larger than those with the conventional design method. With the increase of the floor, the pile body load sharing ratio reduces and the soil sharing ratio increases along with the increase of the upper structure stiffness and the load concentration on the corner pile and side pile. Increasing raft thickness can reduce certain differential subsidence and the average base settlement, thus reducing the secondary stress of the upper structure and improving of the load sharing ratio of foundation soil. At the same time the underraft reaction distribution on top of pile is more uneven, so it is needed to force from the raft and consider raft under the stress of the piles and soils forces comprehensive to determine a reasonable thickness of the raft, which makes the design safety and economy. With the increase of foundation soil deformation modulus, the upper load-sharing by the foundation soil increases, the top of the pile reaction tends to be average, and the maximum bending moment of the raft gradually decreases. Piled raft foundation under the conditions of uniform cloth pile was at the middle edge of the small "dish type" distribution. Differential settlement is due to the upper structure of the secondary stress and raft internal force. Through adjustment of five pile foundation stiffness of foundation soil and pile length, pile diameter, pile spacing, etc, the influence of different foundation stiffness to differential subsidence can be learned. Change in pile lengths of pile form of cloth and combination with the center cloth pile of the foundation soil stiffness adjustment in the form are the optimal design for high-rise building pile raft foundation.