深埋大断面黄土隧道围岩失稳试验研究

Failure modes of surrounding rock of deep-buried large-section loess tunnel

以兰渝铁路黄土隧道工程为依托,采用室内模型试验研究深埋大断面黄土隧道失稳机理,结论表明:①首先边墙部位沿最小主应力方向形成楔形滑移体,然后围岩破坏向拱顶、拱底蔓延,较弱抗拉强度引发黄土拱部围岩松动塌落;②黄土隧道围岩失稳过程:局部裂隙产生→局部裂隙扩展→裂隙急剧贯通→残余强度四个阶段,拱顶围岩松动塌落是边墙剪切滑移破坏基础上出现的;③随着荷载的增大,拱部松动区径向应力先增大后减小,其他测点的径向应力随荷载的施加而增大;边墙处切向应力均随荷载增加而增大,距洞周越近切向应力值增长的幅度越大;④围岩深部存在切向应力升高区,此部分围岩承担着自重与外部土体荷载形成显著压力拱效应,自洞壁向围岩深部依次可分为:松动区→压力拱区→原岩应力区。

Based on the loess tunnel of Lanzhou-Chongqing Railway, mode tests on the instability mechanism of the surrounding rock of large-section loess tunnel are performed. The results show that:(1) The wedge slip is formed on the side-wall parts along the direction of the minimum principal stress firstly and then spread to the vault and arch bottom. The weak tensile strength leads to the loosening collapse on the vault.(2) The instability process is as follows: initiation of local fracture→extension of local fracture→rapid coalescence of fracture→residual strength. The loosening collapse on the vault is on the basis of shear slip on the wall.(3) The radial stress increases as the load applied firstly and then decreases on the vault. The shear stress on the wall increases with the consecutive loading, and the growth rate of tangential stress is greater far away from the hole.(4) The tangential stress-increasing area exists in the deep rock, which bears the self-weight and external soil load and a significant pressure-arch effect is formed. The rock from the wall to the deep part can be divided into three zones: loose zone, pressure-arch zone and initial stress area.