填土对既有浅埋隧道的安全影响及容许填土厚度确定

摘要

既有浅埋隧道上方填土可能导致其衬砌变形、安全系数降低，甚至发生破坏，危及行车安全。以长枪岭隧道上方某拟建公园填土工程为例，选取若干典型断面，对既有浅埋隧道受不同厚度的填土影响进行数值分析，并确定容许填土厚度。结果表明：既有隧道上方填土将导致衬砌整体下沉，左右两侧沉降基本对称，位移值自上而下逐渐减小；填土后的安全系数降低，但幅度不大，拱脚及仰拱处安全系数偏小，可能出现开裂；既有隧道拱顶位移值随着填土厚度的增加而近似线性增大，为满足位移控制要求，容许填土厚度应为0.3H~0.4H(H 为原覆土厚度)。根据若干断面的分析结果可得整个填土区域的容许填土线，在此范围内进行填土施工，并采取相应的工程措施，既有隧道的运营安全可得到保证。本分析方法简单易行，满足工程精度，可用于指导工程实践，对类似工程有一定的借鉴意义。%Soil filling above an existing shallow-buried tunnel probably leads to deformation of tunnel lining and reduction of the safety factor and even leads to destroying of tunnel lining and detriment to traffic safety.The filling proj ect of a planned park to be executed above the Changqiangling Tunnel of the Yangpingguan-Ankang Railway was taken as an example.Selecting some typical sections,the influence of different filling thicknesses on the existing shallow-buried tunnel was analyzed numerically and the allowable filling thickness was deter-mined.The research results indicate as follows:Filling above the existing shallow-buried tunnel causes mono-lithic lining settlement and basically symmetrical lining settlement on both left and right sides and produces gradually reduced displacements from vault to invert of the tunnel;the post-filling safety factors of the mono-lithic lining are decreased but by a not-large magnitude,however,the safety factors of the abutment and vauet become so low as to cause cracks possibly to occur;the displacement at the vault increases almost linearly with increasing of the filling thickness,so the allowable filling thickness should be sets as 0.3H~0.4H(H represen-ting the covering depth of the existing tunnel)to control displacements;by analyzing a number of sections,the curve of allowable filling is obtained for the fill zone,then filling within the range of this curve and adoption of corresponding engineering measures can insure the operation safety of the existing tunnel.The proposed meth-od is simple,easy to execute and accurate in meeting engineering requirements,so it can be used to guide engi-neering practice and provide reference to similar engineering proj ects.