Theory And Application Of Rigid Pile Composite Foundation Under Embankment Loads

The rigid pile composite foundation (RPCF) with individual pile caps combined geosynthetic-reinforcement have demonstrated excellent performance characteristics in ground treatment for highway engineering. RPCF owns technical and economical advantages over other methods, for example , convenient alternating construction, little post-construction and differential settlements, fair consolidation, deep depth of ground improvement, high load capacity and savings of construction time and costs. This type of ground improvement is already taken account into soft ground improvement in highway engineering in China. But it is lack of comprehensive theoretical analysis.The state art of RPCF in soft ground improvement in highway engineering in china is discussed and the key issues are put forward in the paper. Based on the previous researcher's work , the thesis studied the behavior of RPCF under embankment loads via theoretical analysis, numerical simulation and field test. The main contents are as follows(1) The state art of conventional RPCF(composite pile foundation)under rigid loads is reviewed, and the different performance of RPCF under rigid loads and embankment loads is pointed out. The problems need to be solved in the paper are brought out.(2) The proposed model is implemented in an axisymmetric finite element code and numerical simulations are made for the behavior of single rigid pile composite foundation without and with cap under embankment loads. The simulated results indicate that"the plane of equal settlement"and"Soil arching effect"exist in embankment fills. The results also show that the proportion of the magnitude of pile cap size and pile spacing is the key factor to control the load distribution between pile caps and soils between piles. According to the vertical force equilibrium, the equations computing the vertical soil stress acted on pile caps and soils between piles are concluded using multi-arch theory. The equation of computing the stress coupled the geosynthetic-reinforcement is also presented and the equations of calculating strain and stress of are obtained. Finally, the factors affecting the ratio of load carried by pile caps are discussed.(3) Using semi-analytic-numerical method of finite layer method and finite element method, the formulation of the interaction among pile-pile cap-soil in RPCF under embankment loads is put forward. The computing program is made for investigating the behavior of RPCF. From the calculated cases of RPCF under rigid loads and embankment loads, it is pointed out that the behavior of RPCF under embankment loads is distinctly different from that under rigid loads. The soil pressure distribution underneath raft under rigid loads is similar with saddle .But under embankment loads,it increases faster the vicinity of the pile than that in the middle and edge of the pile. At the same load level , the friction along pile shaft is larger than that under rigid loads. The settlement is larger and the load carried by soils underneath pile caps is smaller than that under rigid loads.(4)The Prestressed Tubular Concrete Pile (PTC pipe pile) installation using hammering method causes the increase in pore water pressure of surrounding clays, and the maximum excess pore water pressure is nearly 2 times the effective overburden stress in ground soils. Diameter, length of pipe piles and open-ended or close-ended all affect the excess pore water pressure during pile installation. The excess pore water pressure increases with time during pile installation and dissipates with time after installation. The dissipation time of excess pore pressure varies with the time and the distance from the pile. The dissipation rate initially is larger than later. The longer the dissipation time, the closer the distance is. Cone penetration tests were performed on...