浅埋冻土隧道“抗滑桩+冠梁”塌方处治技术研究

Study on“Anti-slide Pile+Crown Beam”Collapse Treatment Technology for Shallow Frozen Soil Tunnel

处于高寒高海拔地区的浅埋隧道,由于冻土退化形成水(泥)囊,使得砂砾层被地下水不断侵入,导致隧道塌方,而采用普通的维护方案难以有效地进行风险控制。为解决这个问题,以景阳岭隧道出口浅埋段塌方事故为例,提出了“抗滑桩+冠梁”围护结构的处治方案,采用现场监测、有限元模拟等方法对该方案进行了验证与效果评价。还原围护结构施工的部分工序时,把模拟值与对应的现场实测值进行了对比。结果表明:结合地勘资料、超前地质探测报告及现场实际工况,认为围岩条件差、施工干扰是导致景阳岭隧道发生塌方的主要原因;模拟结果与实测结果吻合,表明数值模拟合理,具有对实际工程的可参考性;在增设抗滑桩+冠梁的施工方案后,初支结构的拱顶下沉、拱腰和拱脚的收敛分别为8.9,3,3.1 mm,原塌方轮廓线内的围岩变形最大值也不超过0.18 m,变形均符合设计规范的要求;初支结构受到的最大拉应力位于拱顶,为1.61 MPa,最大压应力位于拱腰,为2.75 MPa,受力均满足设计规范要求;初支结构的拱顶下沉、拱腰和拱脚的收敛分别为5.9,4.3,4.3 mm,最大变化速率0.1 mm/d,均满足原设计要求,表明该方案在实际工程中的治理效果良好;在现设计的基础上,将抗滑桩桩长再减少1.88 m可获得更优性价比。

Shallow tunnel in high cold altitude area,due to the degradation of frozen soil and the formation of water(mud)bags,the gravel layer is constantly invaded by groundwater,resulting in tunnel collapse.However,it is difficult to effectively control the risk with ordinary maintenance scheme.To solve this problem,taking the collapse accident of the shallow section at the exit of Jingyangling Tunnel for example,the treatment scheme of“anti-slide pile+crown beam”enclosure structure is proposed,which is verified and evaluated by means of field monitoring and finite element simulation.When restoring part of the construction process of the enclosure structure,the simulation values are compared with the corresponding field measured values.The result shows that(1)combining with geological exploration data,advanced geological detection report and field working condition,it is considered that poor surrounding rock condition and construction interference are the main causes of the tunnel collapse;(2)the simulation result is in good agreement with the measured result,indicating that the numerical simulation is reasonable and has reference value for practical engineering;(3)after adding the construction scheme of“anti-slide pile+crown beam”,the vault subsidence,arch waist and arch foot convergences of the primary support structure are 8.9,3,3.1 mm respectively,the maximum deformation of surrounding rock in the original collapse contour does not exceed 0.18 m,the deformation meets the requirements of design specifications,and the deformation meets the requirements of the design specification;(4)the maximum tensile stress of the primary support structure is located at the vault,which is 1.61 MPa,and the maximum compressive stress is located at the arch waist,which is 2.75 MPa,the stresses meet the design specifications;(5)the vault subsidence,arch waist and arch foot convergences of the initial support structure are 5.9,4.3,4.3 mm respectively,and the maximum change rate is 0.1 mm/d,which all meet the original design requirements,indicating that the scheme has good treatment effect in practical engineering;(6)on the basis of the current design,reducing the length of anti-slide pile by 1.88 m can obtain better cost performance.