| With the needs of economic development, road and rail line selection tend to be in the form of a long tunnel through the mountain areas, and the long tunnel is likely to be through complicated geological conditions. GuanJiao tunnel, the emphases and difficulties project of the newly built qinghai-tibet railway second line,32.605km long (entrance at the height of3378.72m, exit at the height of3324.10m), is the world's longest plateau railway tunnel at present. In GuanJiao tunnel region, groundwater, rock joints and fissures rock are well developed, the length of fault fracture zone is2782m (single line), medium rich water area17.760km, water bursting pressure up to2.6MPa, and the Maximum water inflow up to9000-9500m3/h. Collapse, deformation and cracking of supporting structure, large-scale sudden flood water phenomenon were frequent in construction. The construction of GuanJiao tunnel is very difficult and dangerous. This paper studies the disaster causing mechanism and control technology of Guanjiao tunnel unfavorable geology, and obtains the following research results:(1) Starting from the data research and engineering practice, water inrush mechanism of GuanJiao tunnel is studied, based on qualitative analysis method. With the surface runoff water test and water link test, supply of water inrush is made clear, On account of geological data, forecast data, design and construction of typical examples of water inrush, hydro geological model of GuanJiao tunnel is summarized. According to the development characteristics of Guanjiao tunnel karst area and the drainage-inrush characteristics of long distance reverse slope inclined shaft, the tunnel face and excavated section inrush mode are put forward. According to the mechanism of water inrush mode, with the theoretical analysis and numerical calculation method, the corresponding countermeasures is put forward. Eventually, a set of comprehensive control technology of water inrush suitable for the long tunnel in northwest karst region is formed.(2) Using the experience summary and field test methods, the conclusion that the pressure on secondary lining of Fissure karst water has the characteristics of local high pressure and increase for a long time is made. Using ANSYS to establish the load structure model, the mechanical characteristics and safety of straight wall and curved wall lining from single track railway tunnel standard drawing under local high water pressure is studied. With analysis of the effect on improving measures to safety factor, the lining design parameters under local high pressure are put forward. The research results fill a gap in lining design basis under local high water pressure.(3) Through research and experience summary, qualitative analysis of the influence of groundwater on rock mechanical properties, revised provisions of groundwater on surrounding rock mass grade from commonly used code are summarized and some useful suggestions are given for the improvement of the revised provisions. Using the method of theory analysis, elastic-plastic solution considering seepage force on tunnel is derived. Through a numerical simulation using the ABAQUS, based on the fluid solid coupling theory, the stress distribution and deformation law of surrounding rock and support structure, with a difference of underground water level, buried depth, preliminary support stiffness and supporting time, are obtained. Based on the theory of loose ring, the design length of bolts is get. Based on the theory of thick wall cylinder, supporting characteristic curve of shotcrete, grid steel frame steel, steel frame and combined support system is get. In the end, combined with the feature of supporting force, the supporting measures in water rich and broken surrounding rock stratum is put forward.(4) Through field test, supporting structure characteristic of the tunnel in water rich and broken surrounding rock stratum is obtained. Based on the loose circle theory, the design length of the bolt is get. Based on the theory of thick wall cylinder, support characteristic curve of shotcrete, grid steel frame, steel frame and composite supporting system is get. Combined with the supporting structure characteristic, some supporting countermeasures for rich water and broken surrounding rock tunnel are put forward.(5) Aiming at the instability phenomenon of fault fracture zone, using field test method, the mechanical characteristics of support and surrounding rock is get. According to the experimental data and theory analysis, the improvement measures of support scheme are put forward. The improved scheme can effectively limit surrounding rock deformation, reduce the damage and geological disasters. It is demonstrated by using FLAC3D to establish a numerical model. Based on the principle of ensuring safety, saving cost and shortening the construction period, further optimization of the radial grouting method in improving scheme is made and a longitudinal partition radial grouting method is put forward. By means of numerical simulation, using FLAC3D to establish the three-dimensional elastoplastic model, three main design parameters of longitudinal partition, grouting distance behind tunnel face, grouting length and grouting spacing, is calculated, and design parameters group satisfying different deformation control effect is obtained. |
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