DEM-CFD Simulation Method Of Strength Evolution Characterisrics Of Fault Fillings

With the development of traffic infrastructure construction in China to the Midwest with complex geological conditions,tunnel and underground engineering construction inevitably encounter fault fracture zones,water-rich karst caves,underground rivers and other adverse geological structures.The disasters such as water inrush,mud burst,collapse,landslide,etc.encountered in the construction seriously threaten the safety of the constructors and the quality of the project.Water-rich fault fracture zone is one of the main geological structures inclined to disasters in engineering geology.The research on the evolution characteristics of the filling structure in the process of seepage failure are deficient.Previous studies on seepage failure through laboratory tests have failed to systematically reduce the evolution of physical field information of filling body.And the numerical method is diff-icult to simulate the strength evolution of filling body.Therefore,it is of great significance to propose a simulation method that can quantitatively describe the seepage effect on the weakening of filling body,and realize the simulation of the catastrophic process of seepage failure of filling body.In this paper,the simulation method of strength evolution characteristics of filling body is the main research content.The variable strength discrete element model is established to quantitatively characterize the seepage failure by means of experimental analysis,macro and micro parameter calibration,and the fluid solid coupling simulation of the seepage failure of filling structure is realized.The evolution law of physical field information in the process of seepage failure is analyzed,and the research results with theoretical value and engineering significance are obtained,mainly including:(1)Based on the analysis of the influence of particle loss on the physical and mechanical properties of the filling body,the erosion rate Caw is introduced to quantify the weakening effect of seepage on the strength of the filling body.Based on the parallel bond model,the DEM model for describing strength evolution characteristics of filling body is proposed.The DEM calculation method of erosion rate Csw is established by integrating particle position retrieval method and bond number retrieval method.(2)Based on the indoor test,the particle gradation of filling medium sample under the condition of erosion rate of 0.0%,4.09%,12.08%,21.88%is studied,and the priority of different particle size in the process of particle loss is obtained.On the basis of previous studies,the functional relationship between erosion rate Csw and permeability coefficient K,cohesion c,internal friction angle ? was established.(3)The three-dimensional discrete element model of consolidation and direct shear test is constructed to carry out the discrete element simulation study,and the particle displacement law,contact force chain change law and stress-strain law in the simulation process of consolidation and direct shear test are analyzed.The relationship between micro parameters such as micro tensile strength ?,micro cohesion c,micro friction coefficient ? and macro parameters such as cohesion c,internal friction angle ?,compression modulus av is studied by using variable control method.(4)The DEM-CFD coupling calculation model is established to simulate the indoor test of seepage failure.Combining the relationship of "erosion rate-shear strength"function and "DEM micro parameter_shear strength" function,the DEM model for describing strength evolution characteristics of filling body is developed.We embed this model into DEM-CFD coupling calculation to realize the seepage failure simulation of filling body,analyze the evolution rule of physical field information such as erosion rate,displacement of filling structure,porosity,stress and strain in the process of seepage failure.And we divide different evolution stages of seepage failure of filling structure.Based on the laboratory test of domestic scholars,the seepage failure law of fault fillings is analyzed,and the reliability of this method to simulate the seepage failure of fault fillings is verified by comparison.