Study Of Analysis Of Water Inflow And Risk Prediction Method Of Water Inrush From Water Bearing Faults In Subsea Tunnel

Unlimited water supply is the distinctive feature of subsea tunnel.In particular,when tunnel gets cross the worse geological section such as fault fracture zone and concentrated joint band,excavation unloading and groundwater cause the instability of surrounding rock,and there will be water inflow,water inrush and other geological disasters.Therefore,it is necessary and crucial to predict the tunnel water inflow and analyze the risk of water inrush scientifically and accurately.Based on the engineering practice of Qingdao Kiaochou Bay subsea tunnel,this paper discusses the analysis of water inflow and risk prediction method of water inrush from water bearing faults in subsea tunnel by the means of theoretical analysis and numerical simulation.Firstly,this paper summarize the research status and advances of the prediction method of tunnel water inflow,the disaster-causing mechanism of water inrush from water bearing faults,and the tunnel risk analysis method.Through the statistical analysis of the safety accident,we know that water inflow and water inrush is the main type of subsea tunnel construction safety accidents.Fractures is developed and surrounding rock is broken and of low stability in the fault fracture zone.So it is necessary,important and urgent to have a study of analysis of water inflow and risk prediction method of water inrush from water bearing faults in subsea tunnel.Secondly,the multi-physics coupling software COMSOL Multiphysics is used to simulate the water inflow from water bearing faults in subsea tunnel.The Darcy equation and the two-medium model of pore-fracture are used to research the influence to tunnel water inflow under the conditions of different rock cover thickness,water depth,the surrounding rock permeability,crack dip and joint spacing.Thirdly,a cusp catastrophe model of water inrush from faults is built to analyze the disaster-causing mechanism of water inrush caused by fault reactivation and water-resisting structure instability.The cusp catastrophe potential function of water inrush from water bearing faults is built and water inrush criterion based on cusp catastrophic model of water bearing faults in subsea tunnel is put forward by the means of the equation of equilibrium surface and the coordinate transformation.Four water bearing faults of high water inrush risk is chosen to calculate the water inrush index in order to predict whether the water inrush happen or not.Meanwhile the advantages and disadvantages and feasibility of this prediction model are discussed.Lastly,based on the Delphi-ideal point method and the catastrophe progression method,nine aspects are chosen as the influence factors including the weathering degrees of the faults,the permeability coefficient of the fillings in fault plane,the fault dip,the width of the faults,the velocity ratio of primary wave to shear wave,the apparent resistivity,thickness of overburden,the distance from the tunnel to the sea level,the construction disturbance.The risk analysis model and assessment system of water inrush of the water-bearing faults in subsea tunnel is built and used to assess the water inrush risk of the 18 large regional faults in Qingdao Kiaochow Bay subsea tunnel.The risk assessment results are consistent with the engineering practice.