Study On Grouting Mechanism And Meso-characteristics Of Sand Based On CFD-DEM Method

Grouting is a widely used geological improvement method.It has engineering applications such as stratum strengthening and anti-leakage.Sand grouting is essentially the process of movement,diffusion and solidification of viscous fluids in porous solid granular media.It involves fluid-solid coupling,large soil deformation,discontinuities,and complex physical and chemical properties of the slurry.Therefore,the macro-meso and fluid-solid coupling mechanism of sand grouting has not yet been clarified.With the rapid development of modern computer technology and calculation methods from the microscopic view,it has become possible to study the grouting mechanism of sandy soil from the microscopic view.In order to further explore the grouting mechanism of sand,this paper innovatively uses the CFD-DEM method.It can offer micro information at the particle level regarding the fluid-particle interaction.the slurry-water interface is determined by the fluid volume method(VOF),which reproduces the sand grouting process.This paper studied the single particle settlement,circular pipe sand seepage,and three-dimensional sand grouting from the microscopic view.The main research contents and results are as follows:(1)Based on the classic case of single spherical particles falling into water,a gas-liquidsolid coupling model is established,and the particle velocity is compared with the classical numerical solution.Which verified the accuracy of the method.(2)The sand pipe seepage flow was simulated,and the Darcy seepage conditions were simulated by applying a pressure gradient difference dp / dl at the boundary.The average water velocity curves of the pipe section under different pressure gradients were simulated.When pressure gradients is small,the velocity is obviously proportional to the pressure gradient,and the linear correlation reaches more than 98%;when the pressure gradient reaches a certain value,the pressure gradient and the average flow velocity of the circular tube section are nonlinear,which is in accordance with Darcy’s law Basically.This verifies the validity of the sandy soil porous media model.(3)Through the rheological test,the influence of water cement ratio on the rheological properties of cement slurry was analyzed,and both the relationship between yield stress and water cement ratio of cement slurry and the relationship between viscosity and water cement ratio of cement slurry were established.Which provides parameter guidance for the later grouting simulation and indoor grouting test.(4)On the basis of the foregoing,the sand soil grouting numerical simulation test and the indoor model grouting test were carried out.Firstly,the diffusion pattern of the grout during sand grouting were compared with the indoor test.The results show that the numerical simulation and the indoor models are consistent.Secondly,through numerical simulation,the effects of grouting speed,slurry characteristics,soil porosity and other factors on the diffusion pattern of slurry,the spatiotemporal change of grouting pressure,and the radial attenuation of slurry diffusion pressure were analyzed.In addition,the porosity change law of the grouting soil layer and the spatial characteristics of the force chain contact distribution are analyzed from a mesoscopic perspective,which provides theoretical support for clarifying the sand grouting mechanism and macro-microscopic characteristics.