Study On Response Surface Method Of Soil Excavation On Additional Displacement Of High-Speed Railway Pier

With the development of road network in China,the crossing between road and railway is becoming more and more common.It is necessary to analyze the influence of new road construction on the displacement of existing railway piers.This thesis takes the existing bridge of High-Speed Railway underneath a road in Jiangsu as the engineering background and established a spatial finite element model.Considering the influence of soil parameter uncertainty on numerical simulation,the parameter sensitivity analysis is carried out,and the form of response surface function is established and analyzed,so as to study the failure probability of pier top displacement within the specification limit.The main work is as follows:(1)The numerical calculation model of the influence of road undercrossing on existing piers is established,and the influence of soil parameters on the displacement of pier top is analyzed by combining the single factor method and orthogonal test method.The results show that the change of pier top displacement is more sensitive to the parameter change of miscellaneous fill layer and silty clay layer,and the influence of unloading modulus in silty clay layer is the most obvious.(2)Using Latin hypercube sampling and Nataf transformation to obtain the sample combination of main soil parameters,and using least squares regression fitting to obtain the second-order and third-order response surface functions representing the implicit relationship between pier top displacement and soil parameters.Through statistical feature diagnosis and accuracy verification,the results show that the calculation error of the second-order and third-order response surface functions is within 2%,which can replace the finite element model,and the second-order function is better than the third-order in terms of fitting cost and function complexity.(3)The excavation depth is used as the independent variable to fit the displacement function of pier top by polynomial response surface.The results show that the prediction accuracy of response surface function considering excavation depth decreases greatly,and the maximum relative error is 14.8%;the influence of parameter correlation on displacement response is analyzed,and it is found that the correlation affects the mean value of the displacement response by less than 1%.The overall influence is small and can be ignored.(4)Based on the second-order response surface function,combined with the MCS method,10~6 calculations were carried out to obtain the failure probability of the pier top displacement under excavation of 1 m,2 m and 3 m.The results show that:under the stricter 2mm limit of pier top displacement,the failure probability of the pier top displacement is close to 0 when excavating 1m and2m,which is relatively safe;when the excavation is 3m,the horizontal failure probability is about 43%,and the security risk is high.(5)The influence of the main distribution types and variation coefficient of soil parameters on the failure probability of the pier top displacement is considered.The main distribution types of parameters have little effect on the displacement failure probability,and the variation coefficient of different soil parameters have a large influence on the displacement failure probability,and the variation amplitude of failure probability is about 6%.With 37 figures,20 tables and 80 references.