Research On Excavation Methods And Supporting System Of High Water Pressure And Water-enriched Soft Rock Tunneling

The construction of high water pressure and water-enriched soft rock tunnels are an engineering problem.As the country invests heavily in transportation construction,there will be more and more tunnels crossing the type of stratum.Therefore,they have important engineering and social significance about researching the tunnel stress-seepage coupling effect,tunnel excavation methods and supporting system,under the high water pressure and water-enriched soft rock geological conditions.Based on the Dazhaiyuan tunnel in Yinchuan-Kunming Expressway,this paper uses numerical simulation,in-situ testing and theoretical analysis to study whether the deformation and mechanical properties of high water pressure and water-enriched soft rock tunnels under fluid-solid coupling are considered.Based upon the fluid-solid coupling,the tunnel excavation methods,initial support structure deformation and mechanical properties,selection of preliminary support and rational support timing of secondary lining are studied.The main achievements are summarized as follows:(1)Using the numerical simulation method to study whether the deformation and mechanical properties of high water pressure and water-enriched soft rock tunnels under fluid-solid coupling are studied.They are obtained that the deformation of tunnel surrounding rock and the stress of supporting unit under two working conditions.(2)The applicability of step-by-step excavation method,CD method and unilateral pilot tunnel method under high pressure and water-rich geological conditions are studied by numerical simulation method.The practical situation of Dazhaiyuan Tunnel is combined.It is suggested that the step-by-step excavation method can be adopted.The stress and displacement of surrounding rock and supporting structure during the construction process are measured in-situ testing.Compared with the results of numerical simulation,the in-situ testing results have the same changing trend,which shows the reliability and feasibility of the method used in this paper.(3)Combining the characteristics of high water pressure and water-enriched soft rock tunnels,the analytical formula of the surrounding rock-supporting characteristic curves is derived,which based on the degradation damage effect of water on surrounding rock,the reinforcement effect of anchors on surrounding rock and the additional damage of water pressure under the high water pressure and water-enriched soft rock geological conditions.The applicability and stability of three initial support structures are analyzed by the convergence-confinement method.(4)The optimal supporting timing of the secondary lining of the tunnel is studied through the theoretical analysis.Using the strength theory and the convergence-confinement method the theoretical analytical formula are derived the optimal support timing of the secondary lining.When the initial support methods of "steel-shotcrete ","grid-shotcrete ","steel,gird and shotcrete" are used,the optimal time period of tunnel secondary lining is 22 d to 28 d,13d to 21 d and 17 d to 24 d.(5)The numerical simulation method is used to optimize the support parameters and the sensitivity analysis of the factors affecting the deformation of surrounding rock is carried out by using the grey relational analysis principle.Combining with the actual situation of Dazhai-yuan tunnel,the optimal support parameters and the main factors affecting the deformation of surrounding rock are obtained.