Numerical Analysis And Study Of CFG Pile Composite Foundation

With the merits such as economy, simple technics and good reinforcing effect, CFG pile composite foundation obtains the rapid promotion in our country, and has gained the good social and economic efficiency. But the theoretical study was far behind the practice, the theory of design and computation was still not mature. There was great difference in some simplification models and computational method, which was difficult to unify. To advance the development of CFG pile composite foundation, the three dimensional model was constructed based on FLAC-3D, and in-depth analysis and study was performed for the work character of CFG pile composite foundation. Besides, LS-SVM was applied to predict the bearing capacity of CFG pile composite foundation. The main task of this thesis are as follows:Firstly, the developing and researching situation of CFG pile composite foundation is reviewed in this paper, and its basic theory is summarized. Besides, the computational method and theory of finite-difference as well as constitutive model adopted in the thesis are introduced.Next, according to the influence factor of the work character of CFG pile composite foundation, the three dimensional model was constructed based on finite difference program FLAC-3D. The bearing capacity, settlement and stress distribui(?)(?) of CFG pile composite foundation are analyzed. Factors influencing axial stress of piles and settlements of CFG pile composite foundation under vertical load are studied. The influence factors include cushion thickness, cushion modulus, soil modulus, replacement ratio, pile length, etc. Some valuable conclusions are made as follows:(1) The settlement of CFG pile composite foundation increases along with the improving of load and cushion thickness;and decrease along with the rise of cushion modulus, soil modulus, pile length and replacement ratio.(2) The pile-soil stress ratio of CFG pile composite foundation increases along with the improving of the load, cushion modulus and pile length;and decrease along with the rise of cushion thickness, soil modulus, and replacement ratio.(3) For the rigid foundation under the vertical load, the distributing rule of axial stress at the same depth are as follows: the biggest is the corner pile, next is the side pile, and the smallest is the center pile.(4) For the rigid pile composite foundation under the vertical load, the cushion can adjust the stress ratio and make both soil and pile put into good use. For one thing, choosereasonable cushion thickness. In addition, cushion modulus can also adjust stress ratio.(5) Under certain load, there is critical length for CFG pile. If pile length is larger than this value, bearing capacity of pile can not improve.(6) Under certain load, the load born by pile increase according to the rising of replacement ratio. Therefore, bearing capacity of composite foundation is increased, and settlement is reduced.Finally, there is great difference between the calculation and site tests. To get reasonable design result, an approach applied to prediction of bearing capacity of CFG pile composite foundation is presented based on LS-SVM. The forecast bearing capacity of composite foundation is in good agreement with the measured data by loading test. The comparison indicates that the accuracy and reliability of the proposed method are better than of BP neural network method.