FEM Analysis For Consolidation Behavior Of Composite Foundation With Long-short-piles

The use of composite foundation with long-short-piles in practical engineering is becoming more and more popular. The design of such foundation and its reasonable evaluation has been deeply concerned by engineers. However, the relevant study on the consolidation behavior of such foundation was rarely reported. In this thesis, the consolidation and deformation behavior of the composite foundation was studied by FEM. The main work includes:1. Software ABAQUS was used to analyze one-dimensional consolidation problem. The result shows that ABAQUS can be used as a good tool in numerical analysis of geotechnical engineering problems.2. A great amount of three-dimensional elasto-plastic analyses were performed on the behavior of composite foundation with long-short-piles, and the effects of some factors such as length and stiffness of long and short piles and the thickness of sand cushion on the consolidation behavior of the composite foundation were carefully studied. The following conclusions were drawn:(1) The rate of consolidation of composite foundation with Long-short-piles is very fast, and the settlement of the foundation reaches to a stable state as long as loading completed.(2) There exist optimal values for module of short pile, the length of both short and long piles, and the thickness of cushion. They should be reasonably determined in the design of the composite foundation.(3) The deformation and pore pressure of sub-layer are affected little by the module of short pile. So we can enhance the bearing capacity of foundation through increasing the module of short pile needing not worrying about the increase of the settlement of sub-layer.(4) The increases of the length of short or long pile in the composite foundation will result in transforming load to deep soil. The deformation of sub-layer will be obviously increased with the increase of the length of long pile.(5) Thickness of cushion do not alter much the pore pressure in the composite foundation with long-short-piles.3. A case study was made by using ABAQUS and the results were compared with field measurement. It confirms again the feasibility of ABAQUS in geotechnical analyses.The work of this thesis indicates that the consolidation behavior of composite foundation with long-short-piles is affected by many factors. So it is suggested that the actual project of ground improvement should be analyzed carefully and optional design should be conducted for the purpose of economy and reasonability.