Study On Pile-soil Interaction Of Bridge In Unsaturated Loess Region Based On Shaking Table Test Of Centrifuge

The fundamental characteristics of loess are under pressure density and unsaturated,and the obvious anisotropy and subsidence in water and earthquake.In the past,most of the research on this aspect focused on the static properties under the vertical load,while the research on the pile-soil dynamic interaction in the loess area under the horizontal dynamic load was very insufficientIn order to study the dynamic interaction of bridge pile-unsaturated loess in Shanxi Province,this paper takes typical Q3 loess from a bridge engineering site in Shanxi Province,applies different excitation forces and vibration waveforms to the vibration table of a geotechnical centrifuge,and studies the dynamic response of the pile foundation of a bridge group.From the test results,the dynamic earth pressure and the pile bending moment show the same mechanical behavior along the burial,that is,the buried depth increases first and then decreases,which indicates that it is reasonable to determine the soil resistance of the pile according to the earth pressure sensor.Method based on mechanics of materials,through processing bending moment of pile and pile lateral soil pressure test data,get the pile lateral soil resistance under dynamic action,namely,relation between p and the relative displacement of piles and soil y power p-y curve,from the point of the results,the power p-y curve shape and the amplitude and vibration time are related,with the increase of the hysteresis loop back area increase gradually,gradually degraded soil stiffness.In addition,there is hysteresis between soil resistance p and pile-soil relative displacement y,and the larger the input amplitude,the more obvious the hysteresisThere are two main unknown parameters pultandy₅₀ in the dynamic p-y model.In this paper,based on the method of reduction coefficient and the static p-y curve of unsaturated loess,the shaft curve of the dynamic p-y curve is obtained,so as to obtain the resistance pult andyso of the limit soil on pile side,and the verification shows that the reduction coefficient PZ=1.4 is applicable to different deptIn order to further verify the correctness and applicability of the dynamic p-y model of unsaturated loess established in this paper,based on the professional anti-seismic analysis software OpenSees,the experimental single-pier model and full-bridge prototype models were built respectively,and the seismic responses of three different pile-soil interaction models（m method,static p-y method,dynamic p-y method）were compared,and the applicability of the three methods in the unsaturated loess area was evaluated respectivelyThe results show that the dynamic p-y model of unsaturated loess can better simulate the properties of soil in practice,and the calculation error of each working condition is within 30%.From the seismic response of the full bridge model,the displacement and internal force response of the pile are mainly affected by different pile-soil interaction models.When the internal force（bending moment,shear force）is the control factor,the m-method model is more conservative,safe and uneconomical.When the displacement is the controlling factor,the m-method model is risky and unsafe,and with the increase of load,the m-method’s displacement response error is larger than the other two models.The calculation results of the static p-y model are closer to that of the dynamic p-y model,which has the advantage of considering the difference of soil properties and the nonlinearity of soil.In addition,the dynamic p-y model is more suitable for the analysis of fine models.The static p-y model can be regarded as a simplification of the dynamic p-y model and is easier to be used in the general finite element software.