In-situ Stress Experiment And Surrounding Rock Stability Research In Deep-buried Part Of Micangshan High-way Tunnel

Micangshan Tunnel has a length of 13.827 km, which is the longest tunnel building right now. It is also the third longest highway tunnel all around the world. The largest buried depth of Micangshan Tunnel is more than 1000 m, and most part of the tunnel is buried more than 500 m beneath surface.When the right side of Micangshan Tunnel reached K40+805, the upper bench of the tunnel was uplifted by rock burst. In the process of excavating, the main tunnel and inclined shaft were influenced by rock burst many times.In order to study the influence of high in-situ stress to surrounding rock, in-situ stress experiment, geo forecasting, monitoring measurement and many other methods in practical field were permitted. According to the results of field and indoor experiment, FLAC3 D was used to analyze the stability of surrounding rock.According to the results of stress relieving method and Kaiser Effect, there exists high in-situ stress situation in surrounding rock. Furthermore, the rock burst happened inside the tunnel was under the influence of high in-situ stress.According to the result of geo forecasting, there is a big influence for surrounding rock in front of excavating surface, and there exists failure of surrounding rock in front of excavating surface. According to geo foresting and field observation, rock burst will not happen in failure and water-containing area. According to monitoring experiment, when excavating, the displacement of tunnel was greatly influenced by rock burst, and there is little influence to the displacement of surrounding rock.Based on FLAC3 D, displacement and stress contours of different excavating methods were obtained. The results showed two-step excavation method is a lot better than one-step excavation method, while three-step method is not a better choice when excavating Micangshan Tunnel compared with two-step excavating method.