基于数值模拟隧道仰拱开挖对初期支护的影响分析

在山岭隧道施工过程中,施作仰拱虽能很好地控制洞室位移,抑制底鼓现象发生,但隧道仰拱的开挖一般都在初期支护基本稳定之后,其开挖会使上部支护结构底角短暂悬空,底角应力释放,从而引起开挖段洞周位移的急剧增加。通过对阎家庄隧道开挖过程的实时监测,分析仰拱开挖前后拱顶下沉和净空收敛的变形量和变形速度,结合ANSYS有限元软件,分析隧道开挖前后初期支护内力的变化。仰拱的施作能使围岩内力分布更加均匀,避免应力集中,但隧道仰拱开挖引起的洞室围岩的变形约占总变形量的25%,需引起施工注意。

Analysis on Influence of Initial Support on Tunnel Invert Excavation Based on Numerical Simulation

In the construction of mountain tunnel, the work of inverted arch may control the cavern displacement and inhibit the floor heaving well. However, the excavation is carried out generally after the initial support is stable basically, which may lead to suspended floor of the supporting structure in the support part and the stress release therewith, then sharp increase of the cavern displacement around the excavated section. Through the real-time monitoring on the excavation of Yanjiazhuang Tunnel, the degree and speed of the deformation of vault settlement and clearance convergence before and after excavation of inverted arch were analyzed and, with ANSYS finite element software, the change of force inside the initial support before and after excavation of tunnel was studied. The work of inverted arch gives more uniform distribution of force inside the surrounding rock and prevents from stress concentration, but the deformation of rock surrounding the cavern caused by the excavation there takes about 25% of the total deformation, which should be paid attention to in the construction.