| With the vigorous development of national infrastructure construction and the implementation of grand statregy of "One Belt One Road ",the traffic and hydropower project have been extended to western region of China,where karstic and mountain widely are distributed.At present,China has become the largest country in the world in term of the tunnel construction scale,difficulty and quantity.Water inrush disasters occur frequently during tunnels are built in these areas,which has become a serious problem theartening construction safety of tunnels and underground projects.According to flow channel and anti-structure,tunnel water inrush disasters can be divided into two types:progressive failure of fractured rock mass and filling structure seepage instability.The type of water inrush due to instability of filling structure refers to that filling structure is revealed in tunnel construction leading to instability of the filling medium then flows into tunnel to form water inrush disasters.This type of water inrush is more likely to form an instantaneous,high-pressure and large-volume water inrush disaster,and the catastrophic evolution mechanism is extremely complex.In this paper,we focused on the object of the seepage-erosion-stress coupling instability mechanism of filling structure and modelling method of water inrush in tunnels.Water inrush catastrophic evolution mechanism due to strength weakening of filling medium under the action of groundwater seepage and hydraulic erosion were deeply studied,and new hydro-mechanical coupling modeling method based on DEM-SPH(Discrete Element Method-Smoothed Particle Hydrodynamics)was proposed.Series of research results with theoretical significance and application value has been achieved.Taking the Yonglian Tunnel fault water inrush and mud inrush,Shangjiawan Tunnel karst pipeline inrush water and water inrush in 3#TBM tunnel of Yinsong water supply project as cases,3D numerical simulation of water inrush disaster due to instability of filling structure have been carried out.The main research achievements are as follows:(1)Based on assumption of three-phase composition of filling structure including skeleton particles-eroded fine particles-groundwater,control equation for elastoplastic deformation of porous media skeleton considering the effect of water pressure is deduced.Yield failure criterion for the skeleton of filling structure is proposed by introducing the Hyperbolic yield failure model considering the combined effect of normal force(compression)and shear force.Based on the force balance analysis for meso-scale particle,critical hydraulic conditions for fine particle erosion are deduced.The control equation for fine particle erosion rate is introduced and then evolution of porosity and permeability of skeleton under fine particle erosion are deduced.The concepts of hydraulic erosion weakening factor is firstly defined,and a constitutive model that can quantitatively characterize the weakening relationship between cohesion and tensile strength of filling medium and hydraulic erosion of fine particles is established.At the same time,a hyperbolic constitutive model that can describe whole process from initial stage of erosion to instability failure of fluid viscosity is introduced,and the nonlinear dynamics control equation of mud-water mixed fluid is established.At last,from the perspective of three-field coupling of seepage of groundwater,erosion of fine particles and stress and deformation of skeleton particles,the instable mechanism of filling structure of "porosity of skeleton increases,bonding strength of medium decrease and viscosity of fluid increase”is explained.The catastrophic evolution mechanism of water inrush is systematically revealed by the seepage-erosion-stress coupling instability of filling structure.(2)Based on principle of particle discrete element method(DEM),a super-quadratic particle shape representing method and accordingly contact detection algorithm are introduced to realize accurate modelling of real particle shape of geotechnical materials.Based on the mechanism of seepage-erosion-stress coupling instability of filling structure in Chapter 2,a DEM hydraulic erosion softening particle-bonded constitutive model was developed,and programmed into traditional discrete element code through Fortran90.The new model has filled the lack of DEM constitutive model in the effect of hydraulic coupling.Using the DEM method combined with the erosion and softening model proposed in this paper,numerical experiments such as compression and direct shear of rock and soil materials were carried out to investigate the relationship between the macroscopic strength of material and degree of hydraulic erosion.(3)According to non-Newtonian flow characteristics of mud-water mixed fluid,a hyperbolic nonlinear rheological model of fluid viscosity is introduced to quantitatively describe the relationship between dynamic viscosity of mixed fluid and erosion rate of fine particles.The nonlinear constitutive model is programmed into the existing SPH solver code.Thereafter classical 2D cavity shear flow,dam break process of fluid were modelled in order to verify the validity of the existing SPH solver.Besides,numerical experiments of impact process of fluid break on a rigid cylinder under different dynamics viscosity of mixed fluid were investigated.It provides a numerical tool for modelling real flow pattern of groundwater in tunnel water inrush process.(4)Considering the features of two-phase components of rock/soil medium and groundwater in filling structure,a dual-medium coupling model based on DEM+SPH was established that the mechanical deformation and failure process of rock/soil media is simulated by DEM method and flow state of groundwater in porous media is simulated by the SPH method.At the same time,a coupling solution strategy suitable for high-efficiency simulation of large-scale particle-based method was introduced to form two-way fluid-solid coupling simulation analysis method.For simulation of complex engineering models,construction method for complex numerical model,hybrid parallel acceleration algorithm based on Linux clusters and three-dimensional visualization processing technology were proposed.Then simulation of dual-medium rotating drum process,and dam-break process were carried out.The simulation results were compared with related experiments or simulation results in publications so as to validate the accuracy of the proposed coupling method.At last,the process of water inrush and mud inrush caused by instability of filling structure was idealized and simulated under conditions of different filling solid levels,particle sizes,fluid particle separation,and coupling mesh sizes,and their flow velocity and accumulation evolution state of mud-water mixture are studied.(5)Based on three typical cases of water inrush induced by filling structure instability,namely water inrush disaster due to filling water-rich fault of Yonglian Tunnel in Jiangxi Province,water inrush disaster due to filling karst conduit of Shangjiawan Tunnel in Hubei Province and the water inrush disaster of 3#TBM tunnel of Yinsong Water Supply Project in Jilin Province,numerical simulations of evolution process of water inrush disaster were carried out through the proposed dual-medium coupling modelling method based on DEM-SPH.In simulation,multiphase flow state of solid and fluid media as well as their mass flow rate at key monitoring sections during the occurrence of water inrush(mud burst)disasters were monitored and analyzed.Finally,for the case of water inrush disaster in TBM tunnel,the normal impact force of water inrush on TBM Cutterhead and its torque power were recorded and analyzed.It shows that the normal impact force dramatically increase at sudden of water inrush,while the torque power of cutterhead continued to increase as the process water inrush.This conclusion successfully explained on-site phenomenon of jam and abnormal work of TBM cutterhead due to water inrush disaster through numerical simulation tools. |
PDF Full Text Request