Research For Bearing Capacity Of CFG Pile Raft Composite Foundation Of Road On The Permafrost

The majority of frozen soil in the Chinese northeast is island permafrost, and its instability of mechanics and heat transfer will pose a great threat to the stability of buildings built in this area. Highways built in island permafrost area have suuffered varied destructions such as settlement, cracking, frost heaving and so on. Thus, how to solve these problems has become the primary issue to many domestic and foreign researchers.This paper relies on the project of Yi-Sui Highway in Heilongjiang Province. The CFG pile-raft composite foundation is combined with the insular permafrost and highway subgrade built in high latitude insular permafrost area are treated with CFG pile-raft composite foundation.Meanwhile, the The bearing capacity test of CFG pile-raft composite foundation and finite element analysis are under way. Here are the main contents and achievements:(1) Test scheme is designed to test the temperature distribution according to the characteristics of CFG pile and permafrost. The test results show that the CFG pile has little effect on frozen soil around the pile and the permafrost freezes quickly after construction. CFG pile and frozen soil bear the static load together after the interaction with a small pile end force. The bearing capacity of single pile CFG is mainly provided by freezing force of permafrost. Thus, frozen soil CFG pile is typical of friction pile. At the beginning of loading time, the relationship between pile end force and settlement is nonlinear, development speed of sedimentation value is faster than the pile end force value. The elastic compression of pile body part is produed, so that the displacement of pile top increases rapidly.(2) According to the results of CFG single pile test, combined with the actual situation of Yi-Sui Highway in Heilongjiang Province, the bearing capacity test method of CFG pile-raft composite foundation are established to test temperature distribution of CFG pile, raft and permafrost. The test results show that frozen soil around the pile will freeze slowly under simultaneous influence of pile and raft.(3) Bearing capacity characteristics of CFG pile-raft composite foundation in high latitude insular permafrost conditions are tested. The test results show that the CFG pile force mode of CFG pile-raft composite foundation is different from single pile force mode. The pile end force of CFG pile-raft composite foundation is about50%of the load.(4) Models of CFG single pile is established with the help of finite element analysis software ABAQUS.According to the numerical modeling analysis, changing characteristics in bearing capacity of the insular permafrost are summarized. Based on the analysis of settlement characteristics of pile and permafrost under different loads, the influence of elastic modulus of pile and permafrost on settlement is confirmed. (5) According to the test results of the CFG pile, raft and permafrost temperature distribution, the boundary conditions on which the frozen soil will melt around CFG pile and soil at the bottom of CFG pile will freeze are concluded. Models of CFG pile-raft composite foundation are created by using finite element analysis software ABAQUS. The proportion of the load of CFG pile to that of the soil is obtained through the analysis on the loads of CfG pile and the soil around the pile. The conclusion of the research on settlement of the whole CFG pile-raft that there is little settlement of CFG pile-raft during the loading process has been drawn.