Experimental Research On Pre-hole Isolation Pile-soil Interaction For Integral Abutment Bridges

Integral abutment bridges is one typical kind of jointless bridge which is the most widely used and has largest number in the world.Compared with the conventional jointed bridges,the expansion joints and bearings on the abutments are eliminated in integral abutment bridges,which could not only fundamentally resolve the durability problem of bridge expansion joint and bearings,but also have better seismic performance than that of conventional jointed bridges due to high redundancy and better integrity.However,because the superstructure and substructure in integral abutment bridges are rigid connected,the pile will carry larger seismic force and become one of the weakest components of integral abutment bridges during earthquake.In order to improve the seismic performance of integral abutment bridge,pre-hole isolation pile was proposed.The pre-hole isolation pile could be constructed by drilling a hole with the larger diameter than the pile cross-section along a certain length of the pile head in integral abutment bridges and filling some typical types of damping materials into the pre-hole.This new technology could reduce the lateral stiffness and increase energy dissipation capacity of integral abutment bridge to improve the seismic performance under earthquake.Based on an integral abutment bridge in China,the pile foundation model test,numerical simulation and formula fitting were carried out.The major work of this paper includes the following aspects:(1)The quasi-static test of four pre-hole isolation pile specimens with scaled ratio of 1:12.5 were carried out in the laboratory,considering pre-hole dimension and filling material as parameters.The hysteresis curves,skeleton curves,energy dissipation capacity and stiffness properties of pre-hole isolation pile was obtained under low cyclic load.The test results show that the shape of hysteresis curve of pre-hole isolation pile filled with rubber particles is full bow,and the hysteresis curve of pre-hole isolation pile filled with foam is more full than that of the pile without pre-hole.The energy dissipation ability of both types of pre-hole isolation pile is good.Compared with the pile without pre-hole,the ultimate resistance of pre-hole isolation pile increases a little,however,the ductility of pre-hole isolation pile decreases a little.The stiffness degradation,displacement and bending moment distribution of different types of piles are similar.(2)According to the measured date of model test,the test p-y curves with different pre-hole dimension and filling material were obtained by the soil counterforce calculation theory.Comparing with API curve and Kim hyperbolic p-y curve,it could be found that the initial stiffness of test p-y curves are changed according to different pre-hole dimensions and filling materials,which are between those of p-y curves of sand and those of p-y curves of filling material.Comparing with the test p-y curves,the initial stiffness of API curve is larger,however,the ultimate resistance is smaller,and the initial stiffness of Kim hyperbolic p-y curve along the pre-hole depth is similar,however,the ultimate resistance is smaller.(3)The finite element models of pre-hole isolation pile with different pre-hole dimensions and filling materials were established by finite element software ABAQUS.The accuracy of the finite element model was verified by the test results.Based on the finite element model,the parametric analysis was carried out.The results of parametric analysis show that the pre-hole isolation pile could effectively increase the energy dissipation ability and reduce the lateral stiffness of pile.(4)According to the results of test and finite element analyses,a hyperbolic p-y curve which is suitable for pre-hole isolation pile was proposed by modifying the initial stiffness and soil resistance of p-y curves.A single pile model was established by finite element software Midas Civil.The stiffness of lateral spring were calculated by the proposed hyperbolic p-y curve and "m" method for single pile horizontal force analysis,respectively.Compared with the results using hyperbolic p-y curve,it could be found that the internal force of pile is larger when "m" method is used.The difference between the results using hyperbolic p-y curve and those using "m" method is small under the small displacement.Therefore,"m" method could only be used to analyze the pile under small displacement.