Water Inrush Mechanism Of Subsea Tunnel Constructed By Drill-blasting Method And Its Application

ABSTRACT:Concerning the feature of subsea tunnel, this study summarizes three different modes of water inrush by the statistical analysis of calamity accident. The method of theoretical analysis, numerical simulation and field test are used to study the water inrush mechanical mechanism of three different modes and the techniques to control the occurment of disaster. The main research results are as follows:(1) Some statistic analysis of tunnel water inrush accident is involved, and the geological conditions, hydrologic conditions, water inrush development process and its mechanism are described when water inrush occurs. We summarize three kinds of water inrush models based on the mechanism of the formation of water inrush channel: hydraulic fracture, formation collapse and structural plane slipping.(2) The paper uses conformal mapping function to solve the stress field of surrounding rock based on complex function method, and the solution concerns the influence of dead weight and water. We take the construction period into account and obtain the effective stress of both short term and long term.(3) The strength factor formula of crack tip of both tensile-shearing crack and compression-shearing crack in surrounding rock is obtained, and the mechanical criteria of tunnel surrounding rock crack based on fracture mechanics is given. We establish fluid-structure interaction model on jointed rock’s cracking, and perform the simulation of hydraulic fracture water inrush, concluding the evolution rule of cracking area and deformation in crack initiation period, fracture propagation period and water inrush channel formation period.(4) A method is put forward to calculate the formation slip angle and judge wether the formation collapse water inrush occurs based on the stress field of the surrounding rock of shallow tunnel. We establish the strain softening model concerning deformation modulus degradation, and by performing simulation of formation collapse water inrush, we get the evolution rule of the failure zone and deformation of surrounding rock during the tunnel contruction.(5) This thesis establishes the tip mutation model of structural plane slipping water inrush in weak-fracture zone, and we get the critical length of slipping plane when the structural plane lose its stability. Based on the contact surface theory, the interaction of different materials on both sides of the structural plane slips were simulated, through which we find the mechanical mechanism of the water inrushes into tunnel in this mode is the relative slipping caused by uneven deformation of the surrounding rock on both sides of the structural plane.(6) Based on the research above, we come up with some control methods of subsea tunnel water inrush including determining the slab thickness, making program of formation reinforcement and reducing construction disturbance, and finally controlling the deformation precisely in the construction of undersea tunnel to reduce the risk of water inrush in undersea tunnel construction.