Suffusion Mechanisim Of Water And Mud Inrush Through Filling Medium In Tunnels

Water and mud inrush geological disasters have always been a huge challenges faced by underground engineering construction such as tunnels,and its manifestations are closely related to the types of structure for prevention of water inrush.The filling medium in filled disaster structure has dual properties of structure for prevention of water inrush and catastrophic structure.The nature of water and mud inrush induced by the instability of filling medium is the seepage damage.According to the chronological order,the whole process of water and mud inrush can be divided into incubation stage,germination stage,and outbreak stage.Among them,the incubation stage is also known as the hidden danger period,and the form of catastrophic change is relatively low degree of variable mass seepage damage—Suffusion.Suffusion is highly concealed and has serious consequences.Clarifying the suffusion mechanism of the filling medium has important significance for the prevention and control of water and mud inrush.This paper studies the suffusion process during the hidden danger period of water and mud inrush in the filling medium of tunnels,including research on continuous nondestructive monitoring,geometric criteria,and multi field coupling of suffusion.A test device for continuous nondestructive monitoring of suffusion was developed,and the spatiotemporal evolution of pore distribution during suffusion was monitored by nuclear magnetic resonance,and the grain size distribution,morphological characteristics and composition sources of fines lost during suffusion were measured based on self-programming.The influence of pore structure parameters on fines loss was analyzed using gray system theory,and the internal stability of the sample was evaluated gradually.In addition,the representative elementary volume of the filling medium was simplified into a two-phase four-component,and a multi field coupling mathematical model for water and mud inrush in the filling medium was constructed.Based on the weak form of equation modeling,the established multi-field coupling numerical model was applied to case engineering,and the spatiotemporal evolution law of various parameters in the suffusion process were analyzed.The main research achievements are as follows:(1)The lower the initial fines content is,the more serious the suffusion is.When the hydraulic gradient is constant,the suffusion process can be divided into development,slow erosion and equilibrium stage.The cumulative fines loss percentage increased exponentially with time.The sensitivity of fines to suffusion increases with the decrease of grain size,while the influence degree of surface morphology on the migration of fines decreases with the decrease of grain size.Suffusion is a complex soil-water interaction process,and the intensity of the interaction is positively correlated with the initial fines content and hydraulic gradient respectively.The d85f of the protected fines decrease linearly with the increase of hydraulic gradient.And the lower the initial fines content,the greater the decrease of d85f.(2)The pore size distribution of the sample has three peaks,and the change amplitude of pore size distribution can reflect the severity of fines migration.For samples with initial fines content of 30%and 40%,overall,the connectivity and heterogeneity of constriction size distribution gradually increase,the complexity gradually decreases,and the equivalent opening size gradually increases during the suffusion.The influence of pore structure parameters on fines loss from large to small is:fractal dimension,nonuniform coefficient,controlling constriction size,and most probable pore size.(3)Through the definition and description of the variables in the change process of the two-phase four-component filling medium representative elementary volume from reference configuration to real-time configuration,a four field multi-parameter strong coupling model was constructed to investigate the mechanism of suffusion during the hidden danger period of water and mud inrush in the filling medium.It was found that the change in the porosity during the suffusion was caused by the joint action of soil skeleton deformation and fines loss.(4)Structural deformation cannot be ignored in the study of the disaster mechanism caused by water and mud inrush in the filling medium.The location with the strongest fluid solid coupling effect is the location with the most severe suffusion.The porosity did not show significant numerical changes and did not fully increase during the suffusion.The locations with the most severe suffusion and the highest increase in porosity are not always spatially consistent.Suffusion and mechanical behavior of the filling medium are mutually causal.The stiffness change of the filling medium during the suffusion was not strictly monotonous.