| With the acceleration of urbanization in China and the gradual densification of subway lines in many cities,it is inevitable for new tunnels to pass under existing lines and there are more and more cases.At present,the characteristics and control standards of each city crossing project show many differences.It is necessary to summarize the existing undercrossing cases,studying the response rules of existing tunnels in different undercrossing forms,and summarize the existing experiences to provide guidance for future projects.Taking 61 undercrossing projects in China as the background,this paper summarizes the characteristics of each project and analyzes the deformation law of existing structures by means of case statistical analysis.Furthermore,according to the typical cases,by means of numerical simulation and monitoring data analysis,Suggestions for optimizing the soil thickness between the old and new structures,the section type of the new station and the net distance between the two lines of the separated tunnel are put forward,and the following main results are obtained:(1)Through the statistical analysis of the basic information of 61 undercrossing projects in major metro cities in China,the differences and generality of undercrossing projects in the aspects of stratum,burial depth,crossing Angle,double-line net distance and soil thickness are studied.(2)Based on the analysis of deformation data and settlement control standards in some cases,the deformation law of existing tunnels was studied,and the influence of various influencing factors on the deformation amount of existing tunnels was analyzed.This paper analyzes the difference of settlement control standard in different places and analyzes the adaptability,and thinks that the control standard in Beijing is the most strict at present.(3)Based on the numerical simulation method and the theory of contact surfaces,respectively,in view of the existing tunnel for the integral tunnel deformation cracks and modeling of shield tunnel,in between the old and new structure of soil layer thickness and double separate new tunnel is reasonable from double net through different conditions was studied,analysis the rule of both the response of the tunnel,and connecting with the practical applicability of the method of optimizing Suggestions were put forward.It is concluded that under the premise of adopting reasonable auxiliary measures to control the soil thickness between the old and new tunnels should be reduced as much as possible.On the premise that the new tunnel is not affected by the existing underground structures and the type of station,when the existing tunnel is an interval tunnel with deformation joints,the net distance between the two lines of the new tunnel is reasonable within the range of 1.5d to 2.0d.When the existing tunnel is a shield tunnel,it is reasonable to set the net distance between 2.0D and 3.0D.(4)Based on the typical cases,establishing deformation cracks and contact between the track and tunnel effect through the method of numerical simulation.The first analysis of single hole under the large cross section tunnel in both the tunnel and the deformation characteristics of the ballast,see rigid deformation features of the tunnel of the union,but as a result of the orbit constraint presents the flexible deformation,ballast and release tunnel structure.And compared with the monitoring data by stages.Then the advantages and disadvantages of single tunnel large section and double tunnel separated station underwear are compared and analyzed,and Suggestions are put forward for the selection of new station section type according to the current development trend. |
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