Pile-Soil Parameters Identification Method Based On Field Load Test Of Single Pile

Based on the analysis and comparison of previous studies, and combining with the ultimate purpose of this paper, the load transfer method was chosen as the basic theory for the pile settlement calculation. All the nonlinear problems should be considered in the establishment of load-settlement relation for single pile were analyzed, and then the transfer function models were given. The transfer character of pile shaft was simulated by tri-line model, which could take into the elastic-perfectly plastic, nonlinear elastoplastic and strain softening characteristics simultaneously and could achieve analytical solutions without complicated calculation process. Bilinear hardening model was selected to simulate the character of pile toe.Based on the load transfer method, basic differential equation of transfer function was derived. The true meaning of parameter S in this equation, which was wrested by some researchers, was clarified in this paper, and some improper perception of S was indicated.The whole process of soil state around the pile was divided into five stages. Based on the basic differential equation of transfer function and the transfer model, and according to the overall equilibrium condition and boundary condition of pile, the load- settlement relation of pile was analyzed. And then analytical solutions of load-settlement relations and pile stiffness in different stages were derived.The in situ static load test result, Q-S curve, was also divided into five stages, which correspond to the five soil stages around pile. Making piecewise fitting for the measured Q-S curve and obtaining fitting equations of each stage, we could calculate the tangent gradient for each point in this curve. Combining the inverse of the tangent gradient and the corresponding analytical expression of pile stiffness under the same load, we could calculate relative parameters in the transfer model. Pile stiffness expressions in different stage relate with different model parameters, therefore, different parameters could be determined from different stages. And in this way, the cross-impact problem of different parameters to the result could be avoided, and the identified parameters would be more reliable.Full use was made of the results of field pile static load test, which is time and labor consuming, to determine the model parameters, and this would save a good deal of trouble caused by other parameter determining experiments. Based on the pile-soil load-settlement relation and calculated model parameters, the settlement characteristics of pile and soil between piles in the same project would be predicted, which would provide fundamental basis for predicting post-construction settlement of pile group.