Stability Analysis Of Soft Surrounding Rocks By Full Face Construction Of Railway Tunnels

With the development of railway construction, more and more railway tunnels are built on mountain areas under great depth and complicated geological conditions.It is very important to control construction time by different excavation methods of long large tunnels. The key technical problems need to be solved during the construction of railway tunnel is to maintain the stability of surrounding rock near the excavated surface and accelerate construction speed.This paper’s research method combines laboratory test, numerical simulation and field monitoring based on Dunhuang-Geermud railway of Dang Jinshan Tunnel. We research different excavation methods and bottom plate preliminary support on influence of surrounding rock’s deformation and stress. It can provide technical support for full face excavation method. The main achievements are as follows:(1)With rock mineral composition laboratory test, it detects mineral composition and contents. Combining monitoring surrounding rock’s deformation, we research mineral composition and content on the influence of surrounding rock’s engineering properties and deformation. The detection results show that the nonmetallic elements contents run up to 70%, much higher than metallic elements contents. Different sample locations have different mineral composition. The total content of quartz and feldspar run up to 73.3% in main tunnel, much higher than parallel and inclined shaft. On the other hand, the contents of illite and clinochlore in main tunnel are much lower than parallel and inclined shaft. With high content of hardness mineral in main tunnel, there is small deformation of surrounding rock. With much low hardness mineral in parallel and inclined shaft, such as chlorite and illite,there is big deformation of surrounding rock.(2)We establish a three dimensional numerical model of tunnel based on floor-load analysis method. In view of Dang Jinshan tunnel surrounding rock of class five, the tunnel are excavated by full face excavation method, benching tunnelling method or core-keeping ring cut method. The result shows that when the tunnel wasexcavated by full face excavation method, the surrounding rock displacement and lining’s stress was bigger than the other excavation methods, but in the controllable range. When the lining is supported by tunnel floor, there is small horizontal displacement at arch springing and lining stress.(3)When the tunnel was excavated by full face excavation method, the field monitoring shows the surrounding rock’s clearance convergence curve and vault settlement was generally align with numerical simulation result. The surrounding rock’s displacement and stress, the lining and bolt’s stress are in allowable range, but we need take some advance support technology to keep the stability of surrounding near the excavated surface.