Macro-scale And Meso-scale Study Of Settlement Mechanism Of Pile Foundations In Sand

The calculation of the pile foundation settlement problem is a hot issue of geotechnical engineering studies, especially the question of the total applied load carried by pile-soil-cap. It's a very complex problem that has been paid attention to by internal and international civil engineers. Under the background of settlement-control composite pile design theory being widely accepted by academics and the engineering, research on the load transfer mechanism at the pile and soil interface and the development of the tip resistance with the pile tip penetration displacement, and how to calculate the settlement of pile foundation, which is the key to optimize settlement-controlled composite pile design theory. According to this subject, this paper does systematic researches on settlement mechanism and load distribution of single pile and pile groups by combinating macro and meso methods. The results are as follows:(1) Based on the plate-shell theory, a pile testing method is established. through affixing the strain gauge on the inside wall of steel tube pile, a perfect numerical analysis method to back-calculate the tip resistance, skin pressure, lateral pressure during the pile driving and static loading process is discussed. Finally it is applicated successfully in Zhengzhou. This method is also used to simulate the single pile and pile group with different density sands in lab meso-scale model test. Microscopic digitization technique for tracing and digital photography deformation measure system is introduced to collect the macro and meso images during each test. The Macro phenomenon of the soil displacement field and stress change field are analyzed during driving and static loading process.(2) The particles flow code analysis models of the single pile and pile group are established, which are introduced to analysis the meso phenomenon of the soil displacement field, friction resistance, tip resistance changing during the single pile driving and static loading process. Finally the influence of pile group behaviors when the distance of pile-pile and the stiffness of cap changing from the micros level are analysised.(3) Based on laboratory tests, particles flow code simulation results and the previous study conclusions, the settlement form of the single Pile in sands is aggregated. Then one nonlinear transfer function of the single pile which can consider the state of sands is proposed. The soil near-field and far field effects are considered in the transfer function, which can be introduced to analysis the relationship of the different density sands and piles interaction. At last the transfer function is verificated by laboratory tests.(4) Stiffness matrix of single pile is established to research the settlement law by introducing the transfer function. After the method being certificated, the load distribution of single pile, the behavior of single pile in different density sands are studied.(5) Based on the analysis of single pile, the stiffness matrixs of pile groups, soils and plate are introduced. Then, the total stiffness matrix of pile-soil-cap is established. The settlement of pile groups and contact pressure of the cap can be solved by the static equilibrium using the total stiffness matrix in the end.(6) Certificated the settlement calculation method of pile groups by laboratory tests results and the previous study conclusions, the settlement mechanism is analyzed of pile group. The different forms between the settlement of single pile and pile group are discussed. Finally the influence of pile group behaviors while the changing of the distance of pile-pile, length-diameter ratio, stiffness of the cap are analyzed.