西南地区变余砂岩浅埋偏压铁路隧道初期支护大变形机理及整治方案

Primary Support Large Deformation Mechanism and Remediation Scheme of Blastopsammite Railway Tunnel Under Shallow-buried and Unsymmetrical Loading in Southwest China

针对西南地区一变余砂岩浅埋偏压铁路隧道洞口段出现的局部大变形、开裂、掉块等问题,通过现场监测和三维数值模拟,分析了初期支护大变形机理,并提出整治方案。结果表明:连续降雨、洞口段偏压严重、围岩等级低是初期支护大变形的主要诱因;右拱腰变形是深埋侧岩体滑动挤压力引起的拉应力和岩层间相对位移产生的剪应力共同作用的结果;左拱腰变形是由于浅埋侧岩体无法抵抗偏压荷载而向外膨胀变形引起的拉应力产生的。采用临时支护+增设排水沟和防水板+喷混凝土护坡+反压减载+长短锚杆组合支护的综合方案进行整治后,初期支护大变形得到很好控制。

In view of the problems of local large deformation,cracking and block falling in the tunnel entrance section of a blastopsammite railway tunnel under shallow-buried and unsymmetrical loading in Southwest China,the large deformation mechanism of the primary support was analyzed,and a remediation scheme was proposed. The results show that continuous rainfall,serious unsymmetrical loading in the portal section and low grade of surrounding rock are the main reasons of large deformation of primary support. The deformation of the right arch waist is the result of the combined action of the tensile stress caused by the sliding compression force of the rock mass at the deeply burden side and the shear stress of the relative displacement between the rock strata. The deformation of the left arch waist is caused by the tensile stress caused by the outward expansion deformation of the rock mass at the shallow burden side,which can not resist the unsymmetrical loading. After the comprehensive scheme of temporary support,additional drainage ditch and waterproof board,shotcrete slope protection,back pressure and load reduction,and combined support of long and short anchor is adopted for treatment,the large deformation of primary support is well controlled.