Failure Mechanism Of Disaster Medium Of Mud Inrush In Tunnel Engineering

Mud inrush disaster is a frequent geological disaster that threatens the construction safety of underground projects such as tunnels and has the characteristics of strong destructiveness and great harm.Large-scale mud inrush disasters(mud inrush amount>10000 m3)are extremely easy to cause serious accidents such as equipment burial and damage,casualties,and even can induce secondary disasters such as surface subsidence.The study of mud inrush disaster mechanism is the basis for preventing and controlling mud inrush disaster.Previous studies on mud inrush disasters have focused more on the inducing effect of geological structure,groundwater,construction disturbance and other external factors on the occurrence of disasters.But neglecting the impact of the mechanical properties of itself of the disaster medium on the can occurrence or not of mud inrush disasters.In this paper,the disaster medium of mud inrush disaster is taken as the research object,and cohesion is taken as the main mechanical index to evaluate its state.The variation of cohesion with void ratio and the critical value of failure cohesion of disaster media were studied theoretically and experimentally.(1)Based on 69 mud inrush cases,the characteristics of mud inrush disaster are studied from the aspects of disaster-causing structure type,mud inrush amount,mud inrush times,medium composition,etc.Reveals the relationship between the mud inrush amount,mud inrush times and the type of disaster-causing structure.Analyzed the solid component of disaster medium,and determined the graded soil properties of disaster-causing medium.(2)The mechanical properties of disaster media are regarded as internal factors,and other factors(in-situ stress,groundwater pressure,construction disturbance,etc.)which affect the process of failure of disaster media are regarded as external factors.Based on the mud inrush cases caused by faults,established the model of mud inrush catastrophe.On this basis,the process of failure of disaster media is analyzed,and it is revealed that the decrease of cohesion caused by the increase of void ratio is the main cause of failure of disaster media.(3)Taken the cohesive force as the main mechanical index for evaluating the state of the disaster medium.Hold soil particles simplified as cubes with different side lengths,and take the arrangement form of soil particles simplified as ordered and equidistant arrangement.A uniform disaster medium structure model is established,and the relationship between soil particle spacing,effective area ratio and void ratio is obtained.The change function of cohesive force of disaster medium is deduced.and the variation law of cohesion with void ratio is revealed.Moreover,the correctness of the function was verified by a direct shear test.(4)Designed and carried out the failure test of disaster media,without considering the influence of external factors,studied the critical cohesion of saturated disaster media.Comprehensive considering the intensity and attenuation characteristics of the disaster medium,a dimensionless index for evaluating the failure risk of the disaster medium,i.e.the " index of mud inrush possibility-k",is proposed.And based on the " index of mud inrush possibility-k" classified the risk level of failure of disaster media.(5)Aiming at the influence of groundwater seepage on the failure of the disaster medium,the hydraulic gradient is used to characterize the seepage,and the influence of seepage on the soil instability is analyzed.The positive correlation between the failure critical cohesive force and the hydraulic gradient is obtained.Then the failure tests and numerical simulations are respectively carried out to verify the results.On this basis,considering the influence of seepage on the failure of disaster medium,the classification method of failure risk of disaster medium is revised.