Composite Foundation And Finite Element Analysis Of The Size Effect Of The Load

With the prosperity of Chinese economy, there are infrastructures in large scales, and the techniques to treat soft soil have developed quickly at the same time. Especially composite foundations are used widely. But the theory is behind the practice in this field. Based on the FEM analysis and load tests in site, some performances of composite foundation are studied.In this research how the length of pile, the rigidity of pile and area replacement ratio of composite foundation affect the stress in the pile, the siding friction transfer law of pile and the deforming characteristics and bearing capacity of the entire foundation is studied. Meanwhile the load transfer laws and the deforming characteristics of single pile composite foundation and group piles composite foundation are researched. Additionally, the deference between the load transfer laws of the inside piles and the side piles and the effect of group piles are analyzed.In the engineering the static load test usually is used to determine the bearing capacity of composite foundation, but the relative specifications in the "The criterion of building foundation treatment(JGJ79-91)" are not so clear. Starting from the effect of group piles in the composite foundation, the size effect in the load test of large area composite foundation, composite foundation of single row piles and composite foundation of double rows piles are researched through FEM analysis. And these are verified by load test in site to validate the conclusion that the testing result on four piles area is closed to the result with the group piles effect in large area composite foundation and to determine the bearing capacity of composite foundation of single row piles and double rows piles, the result from single pile composite foundation is acceptable. Moreover the question of predicting settlement after the engineering finished based on the settlement of load test is discussed.Meanwhile, how the soft interlayer of different place or different thickness affects the load transfer laws and the deforming characteristics of composite foundation are studied, to get the academic basis of the opinion that the hard surface layer should be protect to be utilized and the bearing layer should be good soil.In the end, according to the characteristics of cement mixing piles composite foundation, a practical settlement concluding method for composite foundation is recommend based on theMindlin solution for the centralized force in a half elastic space.