Inclined Surface Under The Conditions Of The Tunnel Face Stability And Surface Subsidence Control Study

In the construction of mountain tunnels, the portal section has bad surrounding rock conditions, which consists mainly of terrene surrounding rocks and the completely-weathered surrounding rocks with the help of the mountains'longitudinal thrust and bias pressure, leading to accidents of roof falling and the cave-in of the heading face at the tunnel portal section. Therefore, the tunnel portal section is always an important and difficult part in tunnel construction.Focusing on geological and engineering characteristics of the portal section, this article goes on field investigations and document retrievals in details about the tunnel heading face's features of collapses, and at the same time uses FLAC3D to do numerical simulation and research on its collapse as well as puts forward related the advance strengthening measures. The mainly research contents are as followings:(1) Specifically analyze engineering projects of collapses of He Yuandong and Shi Zilong tunnel heading face, introducing the process and morphological feature of the collapses, analysing the reasons of collapses, summarizing the project cases of working face collapses at the entrance sections of certain tunnels and the collapse rules;(2) Through FLAC3D, focuse on different working conditions and do numerical simulation for the collapse of heading face of tunnel portral, study its related ground settlement, heading face displacement, distribution of plastic zone, stress redistribution and so on, obtain the morphological feature of the working face unstability at the tunnel entrance section;(3) Put forward the advance strengthening measures to ensure the working face stability, evaluate its effects through numerical simulation, draw a conclusion on the reasonable measures to ensure the heading face stability according to a contrast and analysis.