黄土地区高速公路隧道洞口滑坡变形机理分析

Analaysis on deformation mechanism of landslide at tunnel entrance of expressway in loess area

黄土地区修建高速公路隧道时,时常会遇到由于隧道洞口的施工造成上覆黄土发生蠕滑,使隧道因滑坡滑动而产生变形、开裂等病害,造成隧道无法正常运行。基于上述问题,通过收集黄土地区已发生的隧道洞口滑坡资料,选取6组典型案例分析该类型滑坡的诱发因素与形成条件,结合地质结构模型对隧道洞口滑坡的变形发展过程和运动特征进行了理论分析,并利用数值模拟方法研究隧道洞口开挖对上覆黄土的影响规律,确定隧道在滑坡体中的受力模式,结合典型工程实例对该规律进行验证。研究结果表明:黄土地区隧道洞口滑坡多发生于黄土塬梁地区,坡脚常有冲沟存在,滑坡体主要为第四系风积黄土与马兰黄土,其中人工扰动与降雨入渗为滑坡主要诱发因素。诱发机理为隧道施工坡脚出现邻空面,坡体内部开挖,造成坡体应力重分布,同时坡体在降雨条件下降低了岩土体的力学性质。根据诱发原因,滑坡的破坏机理与形成过程分为4个阶段:隧道开挖应力调整、蠕滑剪切与拉裂、变形加速阶段和坡体失稳。有限元数值模拟案例也很好地反映了滑坡体内的变形场、应力场及破坏区分布,且隧道与滑坡的空间位置关系控制滑坡的性质和规模,研究结果可为后续类似的隧道洞口滑坡提供实践经验与理论指导。

When constructing expressway tunnels in loess area,creep of overlying loess caused by tunnel opening construction often oc⁃curred,which caused deformation and cracking of tunnels due to landslide sliding,and made the tunnels unable to operate normally.Based on the above problems,collected the data of tunnel entrance landslide in Loess area,selected six typical cases to analyze the indu⁃cing factors and forming conditions of this type of landslide,combined with geological structure model to analyze the deformation develop⁃ment process and movement characteristics of tunnel entrance landslide.The influence law of tunnel opening excavation on overlying loess was studied by numerical simulation method,and the stress mode of tunnel in landslide was determined,which was verified by typical en⁃gineering examples.The results show that the landslides at the tunnel entrance in the loess area mostly occurred in the Loess Plateau Beam area and the gullies often existed at the foot of the slope.Landslide body was mainly Quaternary Aeolian Loess and Malan loess.Artificial disturbance and rainfall infiltration were the main inducing factors of landslide.The inducing mechanism was that there was an empty sur⁃face at the foot of the slope in tunnel construction,and the excavation inside the slope caused the redistribution of stress in the slope body.At the same time,the mechanical properties of rock and soil mass were reduced under the condition of rainfall.According to the induced causes,the failure mechanism and formation process of landslide can be divided into four stages:stress adjustment stage of tunnel excava⁃tion,creep shear and tension crack stage,deformation acceleration stage and slope instability stage.The case of finite element numerical simulation well reflects the distribution of deformation field,stress field and failure area in landslide body,and the spatial relationship be⁃tween tunnel and landslide controls the nature and scale of landslide.The research results can provide practical experience and theoretical guidance for similar tunnel entrance landslide.