Research On The Load-Transfer Mechanism And Interaction Of Long Concrete Piles

The pile is one of the foundations used extensively in civil engineering. Aiming at the problems existing in the engineering applying of the long pile, based on the data of the in-situ pile load tests and the results of the model tests, the systemic study of the bearing capacity behavior and the deformation characteristic of vertically or horizontally loaded piles is carried out. The main contents of this paper include the testing study of the physical and mechanical feature of the interface between the pile and soil, the investigation of the vertical bearing mechanic and the ultimate bearing capacity determination of the single pile, the analysis of the mechanic and the calculating methods of the piles, and the research on the bearing and deformation behavior of laterally loaded piles.To begin with, the physical and mechanical characteristic of the interface between the pile and soil determines the bearing behavior and the deformation feature of piles directly. Therefore, the shearing model test of the interface between the concrete block and the silt is performed. The test results show that the load-deformation (Ï„-z )curve of the pile-soil changes from the single humped curve to the hyperbolic curve, along with the increasing of the vertical pressure. That implies, under the lower pressure, the load transfer characteristic of the soil interface is intenerated, otherwise, it is strengthened. Meanwhile the water content and the voids ratio influence the mechanical feature of the interface mostly. There exists the optimum water content, where the friction of the pile-soil is peaked. On the other hand, at the initial stage of shearing, the shearing modulus is maximal. However the modulus decreases with the shearing deformation increasing. According to the analysis of the tests, the nonlinear-plastic load transfer model is put forward to simulate the interaction mechanic between the pile and soil.Consequently, based on the analysis of the field load tests, it is concluded that the load transfer behavior of the super-long friction pile is similar to that of the end-bearing friction pile, for its P-S curve is smoother than the pure friction pile's. Coupled with the intenerating and strengthening effects and considering the influence of the overburden pressure, the calculating method of the pile ultimate bearing capacity recommended by the actual technical codes is modified. On the basis of the statistical analysis of substantive pile load tests, the intenerating and strengthening coefficient of soil with different buried depth, and the end bearing modifying coefficient are presented. Furthermore, the double-coefficient method, with the initial shearing modulus and the water content, is suggested to evaluate the ultimate friction of the pile side, which improves the disfigurement of actual evaluating methods.Furthermore, combined with the finite element method of one-dimensional rod structure and the classic load transfer approach, the hybrid method is presented to analyze the single pile settlement. In this method, the nonlinear-plastic load-deformation model is applied to simulate the load transfer feature along the whole pile in non-linear soil. At the same time, to compare the calculating precision, the trilinear load-deformation model is also used. The results computed by the two models keep good relationship with the field test data. However, the nonlinear-plastic load transfer model is more advantageous for its concision and non-linearity. Considering the interaction of the pile group, the layered soil model is referred, which makes calculation of the interaction coefficient much more convenient. More ever, the mechanic of"restrain"action among piles is studied fully, and the iterative method is established to compute the"restrain"action. Then the approaches mentioned above are applied to several cases, and the rule of the settlement of pile group influenced by the different pile designing coefficients, is summarized.Finally, the combination approach of the soil's p-y curve method and the finite method of elastic beam member is utilized to analyze the laterally loaded piles. To simplify the calculating process, the shallowest depth presented by Briaud, where the shear force in the pile is zero, is cited. For the pile group under lateral load, the interaction mechanic has been analyzed deeply. It is pointed out that, under the horizontalload, there coexist the'subtract'action and the'superpose'action. Therefore, the'front-subtract and back- superpose'model is established to analyze the interaction between piles. And the calculated results of two cases keep an excellent accordance with the field data.