Three Dimensional Nonlinear Finite Element Modeling Of CFG-Lime Pile Composite Foundation

Soft clay strata are often found unable to bear the load transferred from the superstructure to the foundation. The reason behind this low bearing capacity may be low shear strength and high compressibility of the soil in in-situ condition. Ground improvement technique plays an important role in such cases. The problem of constructing highly loaded structures on soft soil can be overcome by adopting ground improvement techniques. Different techniques for ground improvement are available in geotechnical field, but the use of these techniques depends on the type of the project. In order to mobilize shallow soil to participate in the interaction of pile sufficiently, the concept of pile is extended to a new type of foundation named multi-pile composite foundation. In the system of multi-pile composite foundation, more than one type of piles with different lengths and diameters can combine to form the composite foundation. CFG and lime piles are two commonly used ground treatment methods and have been used effectively in many applications of ground improvement in China to increase the bearing capacity and reduce the settlements of ground. When CFG and lime piles are combined to form multi-pile composite foundation, there are always some difficulties when dealing with this type of multi-pile composite foundation in design and construction. The research results at home and abroad of multi-pile composite foundation are summarized. The reinforcement mechanism, characteristics of bearing capacity and deformation of CFG and lime pile composite foundation are respectively introduced. The advantages formed by CFG and lime piles are introduced. The calculation methods of bearing capacity and settlement and testing methods of CFG and lime piles composite foundation are put forward. The main focus of this thesis is to study the load-settlement behavior of this new type of composite foundation subjected to different uniformly distributed load using three dimensional nonlinear finite element analyses by changing the values of the parameters, including the piles length, piles diameter, and cushion thickness. Also study the stress distribution of the composite foundation and influences of the cushion on load-settlement behavior and stress ratio of piles to subsoil. The results show that the settlement is greatly affected by the length and diameter of the CFG pile. Moreover, it is noted that the load-sharing ratios of piles to subsoil is noticeably affected by the cushion thickness. Several suggestions have been made for the further research on multi-pile composite foundation formed by CFG and lime piles.