The Bearing And Stability Characteristics Research Of CFG Composite Ground Under Flexible Infrastructure

Along with the development of high-speed railway, highway, and dam construction, because of the low cost and good effect, CFG pile composite ground has been widely used, research about bearing properties on composite foundation under the flexible foundation is increasingly valued. At present, the research on design method of composite foundation under the flexible foundation is not yet mature in our country, it causes some difficulties for our country to design and implement the design specifications on road-bed of railway. Therefore, systematic comparative study on the bearing properties of composite foundation between rigid foundation and flexible foundation, improve the design method of composite foundation under flexible foundation is a problem to be solved urgently.In this paper, we compare and analyze the similarities and differences about the settlement, loading sharing of piles and soil and the loading transfer of the CFG pile composite foundation under different influencing factors through literature investigation, centrifugal model test, numerical simulation, we make a deep analysis on the bearing properties about the CFG pile composite foundation under the flexible foundation, obtain some main results as follows.1. Foundation stiffness has a great influence on subsidence deformation of the CFG bearing pile composite foundation, the upward pierce of pile under rigid foundation is more significant than that under the flexible foundation. The design of thickness and strength of the cushion layer should be paid sufficient attention, so that the cushion layer can have a good adjustment in the pile-soil loading share.2. Under the same loading level, pile-soil stress ratio and pile-soil loading share ratio are closely related to the foundation stiffness in the CFG bearing pile composite foundation. The bigger the foundation stiffness, the bigger the pile-soil stress ratio, the more the pile loading, the strength of the pile can exert more adequate.3. The settlement of CFG friction pile composite foundation are greatly influenced by the foundation stiffness and pile spacing, the scope of reinforcement has limited influence on the settlement of CFG friction pile composite foundation. In situations where geological conditions enabled or request of post-subsidence is not high, we can try to narrow the reinforcing scope of CFG pile, it won’t bring larger increment and can reduce the engineering budget.4. The neutral point of bearing pile is lower than that in friction pile, that is to say, bearing pile undertakes more negative friction than friction pile, too much negative friction can reduce the safety degree of the strength of pile body, which in turn failure occurred. Therefore, it is necessary pay enough attention to the negative friction for bearing pile in the design of the high-speed rail.5. Piles of different location play different role in composite foundation stability, in subgrade center, pressure is the main, in slope toe, bent-resistant is the main, between them, bending and shearing resistance is the main. As a result, the destruction of the composite foundation is not an overall destruction, but a gradual destruction, namely local destruction causes the overall instability.