Expansion Of Water Inrush Channel In Tunnel By Water Erosion And Seepage

Water and mud inrush is a common geological disaster in tunnel construction,which occurrence frequency,economic loss and casualties rank first among all kinds of geological disasters.The key to the study of water and mud inrush is the mechanism of water and mud inrush.The expansion of water inrush channel is the main reason for the further development of disasters,and the loss of side wall particles is the key factor leading to the expansion of water inrush channel.Therefore,in this paper,the expansion mechanism of water inrush channel is systematically studied by means of theoretical analysis,laboratory test,numerical simulation and engineering example.(1)In terms of the mechanism of water inrush channel expansion in tunnel,Taking full account of the position relationship between particles,the three-dimensional stress state of the particles on the water inrush channel side walls under the action of water scour and seepage is analyzed,and the dynamic model of the particle starting is established.The critical starting velocities of particle for sliding instability,rolling instability,and lifting instability are deduced.The determination method of particle starting is proposed,and the mechanical mechanism of water inrush channel expansion is revealed.The main conclusions are as follows:(a)The particle starting velocity first decreases and then increases with the increase of particle size,and it is the minimum when the particle size is about 0.6 mm.The starting velocity of sliding instability is obviously greater than that of rolling instability.The particle starting velocity increases with the increase of particle density and friction coefficient.(b)The particle starting velocity generally decreases with the increase of three-dimensional relative exposure.The particle starting velocity first decreases and then increases with the increase of slope dip angle and seepage force direction,and decreases linearly with the increase of hydraulic gradient and pore ratio.(2)In the laboratory experiment of water inrush channel expansion,the basic physical and mechanical parameters of sample are obtained by conventional triaxial and other basic mechanical tests.The physical model test of water inrush channel expansion is designed,and the expansion standard of water inrush channel is determined according to the three motion states of particle(individual movement,ounce movement and universal movement).Finally,the experiments of water inrush channel expansion under different particle size groups are carried out.The main conclusions are as follows:(a)The critical state of individual movement and ounce movement is set as the standard for the expansion of the water inrush channel.(b)With the increase of particle size.the channel shape deformation is more obvious,while the sample content of gushing water first increases and then decreases.(3)In the numerical simulation of water inrush channel expansion,the DEM-CFD coupling is used to realize the numerical simulation of water inrush channel expansion.Based on BP neural network.the nesoscopic parameters of granite particles are inverted and calibrated through the discrete element simulation of conventional triaxial test.The expected value of the particle staring velocity considering the randomness of the particle position is obtained by calculating the probability distribution of 3D relative exposure in different slope dip angle.Finally,the expansion of water inrush channel under different particle size groups and different slope dip angle is simulated.The main conclusions are as follows:(a)Particle starts mainly along sub-surface two particles.For the region(0°～30°),the distributions of two relative exposures in the x direction basically conform to weibull distribution.For the region(30°～60°).the distributions of two relative exposures in the x direction basically conform to the uniform distribution and weibull distribution respectively.For the region(60°～90°).the distributions of two relative exposures in the x direction basically conform to weibull distribution and exponential distribution respectively.The joint distribution of two relative exposures in the y direction shows the characteristics of "multi-peak".(b)The results of numerical simulation and experiment are close to the expected theoretical starting velocity under rolling instability in the region(0°～30°),which indicates that the critical instability of particle is mainly rolling,and the critical velocity of water inrush channel expansion is determined by the starting velocity of particle near the bottom of the slope.