Study On Surrounding Rock Groutability Of Saturated Sand Tunnel Under Moving Water Condition Based On CFD-DEM

At present,the development and construction of underground space in China is very hot,and many projects involve the geology of saturated water-bearing sand layer.Grouting technology is a low-cost and effective measure in stratum reinforcement,so it has been widely used in tunnel construction of saturated water-bearing sand layer.At home and abroad,many research achievements have been made in the grouting treatment of sand layer,but there are few studies considering the influence of groundwater,and the flow scour in saturated water-bearing sand layer has an important influence on the grouting effect,so the study on the influence of flow scour on saturated water-bearing sand layer has an important engineering application value.In this thesis,on the basis of the existing research on grouting injectivity,the PFC discrete element simulation program is used to simulate the grouting process of sand layer,focusing on the influence law of moving water velocity on the grouting injectivity of sand layer,and the influence law of sand permeability and grouting pressure on grouting injectivity.The main research contents and conclusions of this thesis are as follows:（1）By looking at the existing research literature at home and abroad,combing the current system of the saturated sand layer surrounding rock grouting governance issues of research results,this thesis using the discrete element numerical simulation method of sand layer surrounding rock grouting process,the basic principle and method and soil characteristic parameters of the factors affecting the stability of sand tunnel,mainly discusses PFC3 D software related features and using method,The results of previous calibration were used to calibrate the mesoscopic parameters,and the triaxial simulation test and DEM fluid modeling method were used to analyze the macroscopic characteristics of the mesoscopic reaction materials.（2）The influence law of sand permeability,grouting pressure and underground flow velocity on grouting reinforcement in tunnel with saturated water-bearing sand layer is discussed,and its influence on grouting feasibility of surrounding rock with saturated water-bearing sand layer is studied.（3）There is a positive correlation between the permeability of sand and the diffusion of grouting slurry.In the simulation test,the maximum change rate of the equivalent sphere radius of grouting slurry diffusion is 2.02%,the change of grouting slurry diffusion in the longitudinal direction is more obvious than that in the transverse direction,and the slurry has an obvious trend of diffusion along the interface between pipe wall and sand.（4）The increase of grouting pressure is beneficial to the injection of grout in sand layer.The numerical simulation results show that the equivalent radius of grout diffusion range under 1000 k Pa grouting pressure is 7.39% larger than that of the test group under 500 k Pa grouting pressure.（5）The erosion of water flow has an obvious influence on the reinforcement effect of grouting grout,and the grout loss rate in the core area of grouting increases with the increase of water flow velocity.Under the erosion of 5m/d,10m/d and 15m/d,the grout loss rate in the core area of grouting reinforcement is 19.83%,33.47% and 44.42%,respectively.The influence of flow erosion on grouting injectivity is greater than that of grouting pressure and sand permeability.