超浅埋隧道施工变形特征实测研究

Field measurement study on deformation characteristics of a constructing ultra-shallow tunnel

当隧道埋深达到超浅埋隧道标准时,围岩应力状态和支护结构内力状态会变得极其复杂,严重降低隧道施工安全性,因此,有必要针对超浅埋隧道施工过程中的各项变形特征开展研究。以胡营西山隧道为工程背景,对净空收敛、拱顶沉降、地表沉降、钢拱架应变及二次衬砌应变进行全程监测及实测数据分析。主要结论如下:1)超浅埋隧道地表沉降均呈沉降槽分布,最大值在隧道顶部;2)周边收敛和拱顶下沉均随时间递增,且前期增速较大,后期趋于平稳;3)钢拱架初期应变值增长较快,每一台阶开挖都会对应变造成一定的影响,使应变发生重分布;4)因为混凝土凝结过程放热,二次衬砌的初期应变值都由拉应变转变为压应变,前期拉应变快速增长。

When the buried depth of a tunnel reaches the standard of ultra-shallow,the stress state of surrounding rock and internal force state of the supporting structure will become extremely complicated,which seriously reduces the safety of the tunnel construction.Therefore,it is necessary to study the deformation characteristics of ultra-shallow tunnel construction.In this paper,taking Huying Xishan tunnel as the engineering background,the perimeter convergence,vault settlement,surface settlement,steel arch strain and secondary lining strain were monitored and analyzed.The main conclusions are as follows:1)The surface settlement of ultra-shallow buried tunnels is distributed in a settlement groove,and the maximum value is at the top of the tunnel;2)Both the perimeter convergence and the vault settlement increase with time,and the growth rate is large in the early stage,and tends to be stable in the late stage;3)The strain value of a steel arch increases rapidly in the initial stage,and each step excavation has a sudden influence on the strain,resulting in the redistribution of strain;4)The initial strain of the secondary lining changes from tensile strain to compressive strain,and the early tensile strain increases rapidly,which is caused by heat release in the concrete setting process.