Study On Disaster Mechanism Of Water Inrush In Deep Karst Tunnel Based On Damage Evolution

With the development of traffic construction in China,tunnel engineering has become an important part.Tunnel construction is gradually transferred to southwest mountainous areas with complex terrain and geological conditions,and presents a trend of "large buried depth,long tunnel line,high stress,strong karst,high water pressure,complex structure and frequent disasters".This paper takes a actual karst tunnel fault as the research object,establishes a mechanical model of rock stress-seepage-damage according to the basic theory,analyzes the coupling process by numerical software,and studies the water inrush mechanism of tunnel fault in karst area.The main research contents include:(1)The representative element theory is introduced to describe the microstructural changes of rocks.Based on the theory of elasticity,a statistical constitutive model of rock damage based on Weibull distribution is established.At the same time,the evolution equations of porosity and permeability are derived based on the theory of seepage mechanics.The strain variable of the rock element is selected to calculate the damage variable.An evolutionary mechanics model of rock damage is established under the coupled action of stress and seepage.Then the maximum tensile stress criterion and Mohr-Coulomb criterion are used to judge whether every elements damage and its damage value.Conventional rock triaxial compression tests are carried out to verify the reliability of the constitutive model.(2)Based on COMSOL Multiphysics numerical software and MATLAB,the program is written and the finite element numerical algorithm is established.The Wei Bull-distribution is used to describe the natural heterogeneity,strength and permeability of rocks.Through the numerical simulation of rock uniaxial compression,biaxial compression and hydraulic cracking,the laws of crack propagation and microelement damage of rock are analyzed.With the help of literatures,the mechanical model is verified and improved.The simulation results show that the inhomogeneity of rock can affect the stress and damage of rock,and the mechanics model of rock damage is reasonable in some extent.(3)Taking the actual karst tunnel as the research object,a fault water-inrush model of karst tunnel is established.Firstly,the nonlinear seepage mechanism and non-Darcy effect of water inrush under excavation step are analyzed.Then,through tunnel excavation,the stress field,seepage field and damage of surrounding rock,as well as the influence of ground stress on surrounding rock are researched,and the mechanism of water inrush and the cause of disaster are analyzed about karst tunnel fault.The simulation results indicates that the water burst from karst tunnel fault shows nonlinear seepage characteristics.In the process of long-term groundwater erosion,the fault develops into a good water passage gradually,which affects the stability of tunnel surrounding rock.The paper include 71 figures,7 tables and 120 references.