MODEL TEST AND NUMERICAL ANALYSIS OF BEARING CHARACTERISTIC OF NEW RAFT FOUNDATION UNDER SEASONAL FREEZE-THAW CONDITION

The strength of foundation in island frozen soil decreases sharply as the frozen soil thaws,which leads to uneven settlement of the subgrade. Hence,we propose a new raft structure for the highway in island frozen soil area in this paper. In order to study the bearing characteristics of the new raft foundation,the freeze-thaw cycle,ramp load tests and numerical simulation method are applied on the new raft foundation model. We analyze the bearing characteristics of the new raft foundation and how the freeze-thaw cycle affects the deformation and the stress distribution of foundation model and the strain of the new raft structure. The results show that the bearing effect of the new raft greatly alleviates the foundation deformation and reduces the foundation stress within a certain depth,which indicates that the raft exists as a "reinforced structure" of the foundation. The larger stiffness of the new raft allows the load to be transmitted to the periphery,reducing the foundation reaction force at the center of the raft. The strain of the new raft presents a U-shaped distribution with large in the middle and small on both sides. Meantime,the longitudinal strain is higher than the transverse strain,indicating that the deformation is transmitted more along the longitudinal direction of the raft. The soil structure is seriously damaged by the freeze-thaw cycle,resulting in a significant increase in settlement of foundation. The raft-soil system shares the upper load,and the raft strain increases while the soil strength decreases. Besides,the increase of stress in a certain depth range of the foundation caused by freeze-thaw cycle is consistent with the depth range of freeze-thaw cycle action,and the degree of influence becomes more obviously with the increase of the load level. In addition,the numerical simulation results are in good agreement with the experimental results,which indicates that the numerical simulation method can be used to analyze the mechanical characteristics of the new raft foundation in island frozen soil area.