黄土隧道围岩压力拱效应分析

Analysis on Pressure-arch Effect of Surrounding Rock in Loess Tunnel

以兰渝铁路大断面黄土隧道工程为背景,采用数值计算和模型试验对黄土围岩压力拱效应进行分析,可得结论:(1)由于荷载传递路线发生偏转,拱部围岩切向应力因承担径向传来的荷载而增加,且离隧道边界越近应力增幅越大,压力拱边界向围岩深部扩展。(2)靠近隧道洞周,边墙处应力路径切向应力、径向应力低于原岩应力,切向应力表现出较强的应力集中,径向应力只有小幅增加。(3)相对于黏性土,黄土抗剪强度较小,需要更大范围的土体参与承受围岩压力,致使压力拱外边界远离隧道断面;黄土围岩压力拱边墙处最大,拱顶处次之,拱底处最小。(4)黄土围岩破坏过程表现为局部裂隙产生、局部裂隙扩展、裂隙急剧贯通、残余强度等4个阶段;拱顶松动塌落出现在边墙剪切滑移破坏基础上。(5)数值分析与模型试验所得黄土围岩压力拱的范围基本相符,验证了压力拱的客观存在;压力拱承担着自重与外部土体荷载,自洞周向围岩深部依次为松动区、压力拱、原岩应力区。

Taking the large-section loess tunnel proj ect of the Lanzhou-Chongqing Railway as the background, the pressure-arch effect of loess surrounding rock was analyzed by model tests and finite element numerical cal-culations.The results show as follows：（1）Due to deflection of the load transfer path ,the tangential stresses of the portion of the pressure arch ring bear radial loads and so increase;the closer to the tunnel boundary ,the greater the increasing magnitude of the tangential stresses,and the pressure arch boundary develops to deep surrounding rock.（2）Keeping to the stress paths in side walls at the tunnel ring,the tangential stresses and ra-dial stresses are lower than the original rock stresses,the tangential stresses show strong stress concentration and the radial stresses increase slightly.（3）Compared with clay soil,the shear strength of loess soil is rela-tively small,thus requiring a wider range of soil body to bear surrounding rock pressures and causing the out-side boundary of the pressure arch to get far away from the tunnel section;referring to the loess surrounding rock pressure arches,the pressures are the largest at side walls and the smallest at arch bottoms and lie in be-tween at arch tops.（4）The fracturing process of loess surrounding rock：undergoes four stages,i.e.,genera-tion of local fractures,expansion of local fractures,rapid through fracturing and retention of generation of re-sidual strengths;vault loosening and collapsing occur upon side wall shear slide.（5）Numerical calculations and model tests yield the basically identical ranges of loess surrounding rock pressure arch,thus proving the exist-ence of the pressure arch;the pressure arch bears its self weight as well as the external soil loads over the areas of loosening,pressure-arch and initial stressing from the tunnel ring to deep surrounding rock.