Research On The Influence Of Water Content On Stability Of The Surrounding Rock Of Tunnel In Xigeda Strata And The Controlling Techniques

The "Xigeda" strata is a kind of silty mud-stone that peculiarly distributed in the Pan-Xi area, Sichuan Province. It is characterized by the highly weathered rock, which would disintegrate and dissolve to slurrying state upon water encountering. The calcareous siltstone is sandwiched into the taupe pelitic siltstone, which is highly weathered and quite soft. The surrounding rock could not be self-stabilized and has an extremely low compressive strength. It is a kind of argillaceous sandstone that is extremely unstable. The experience of the transportation construction in the Xigeda strata indicates that, the construction activities may induce several disasters, such as landslide, collapse, water percolation, softening, rheology, and the deformation of the surrounding rock, etc. At present, the projects that cross the Xigeda area are facing increasingly prominent geological problems. The technological immaturity in several aspects has been lagging behind the regular construction of the highway and railway, which cannot meet the requirement of the rapid development of the transportation construction.This thesis is based on the capacity expansion project from Miyi to Panzhihua, a segment of the newly built Chengdu-Kunming railway. Methods including In-situ investment, data access, numerical simulation, indoor soil test are combined to proceed the research. Aiming at the special engineering property of the Xigeda strata, which would disintegrate and soften upon water encountering, the indoor soil test is adopted to study the influence of the water content on the mechanical property of the surrounding rock, and the existing domestic results are combined to determine the sub-classification of 5 kinds of surrounding rock in the Xigeda strata.The strength reduction method is introduced to serve as the stability assessment method of the surrounding rock. The criteria of instability is whether a sudden change of the displacement at the characterized point of the tunnel occurs. The numerical simulation is combined to study the influence of the water content on the stability of the surrounding rock, and quantitative stability assessment method of the surrounding rock of the tunnel in the Xigeda strata is proposed.Finally, the feasibility of the the existing common stability-controlling construction method to the tunnels in the Xigeda strata is analyzed. According the feedback from the designing and the construction company, the study emphasizes on the stability controlling effect of the short step based and super-short step based three-step method with the feet-lock bolt combined.