Numerical Simulation Of Seepage In Water-rich Pebble Formation With Coupled CFD-DEM

In rencent years the excavation in underwater becomes a new condition in the construction of Beijing Metro.The appearance of this condition add many difficulties to the building of the underground railway,especially in how to effectively restrict groundwater level and the underground supporting.The seepage between coarse particles of this condition is ragarded as a special solid-liquid two-phase flow.Therefore,this dissertation builds the Python-PFC3 D coupled program for this condition accroding to coupled CFD-DEM.In the process of establishing Python-PFC3 D coupled program,the governing equations of the solid-liquid two-phase flow and the forces between solid and liquid are displayed respectively.The forces acting on the particles are analyzed and selected emphasically,while the solution of the Navier-Stokes equation is discussed.After establishing the Python-PFC3 D coupled program,the examples are applied in validation of the program,which include the solidification of single particle in a static fluid,the migration of particulate material in a low Reynolds number porous flow and the accumulation of particulate material through a funnel.The verifications show that the results of the coupled program are the same as those the examples given.Therefore,the Python-PFC3 D coupled program established can simulate the phenomenon in the actual conditions of engineering.After verifying the accuracy of the Python-PFC3 D coupled program,a numerical simulation of the seepage in water-rich pebble formation of metro station is carried out.By establishing the particle-fluid coupled model below the bottom of the diaphragm wall,seven different kind of conditions of solid-liquid coupled are simulated,which takes the pressure of inlet surface and the thickness between the bottom of the diaphragm wall and the lower aquifuge as variables.And the particle displacement and velocity distribution in the solid-liquid coupled field were analyzed.The results show that with the pressure of inlet surface increasing the particle displacement increases in the value of displacement and the number of particles.The velocity of flow field increases as well as the particle displacement.On the outlet surface,the larger values of particle displacement and velocity of flow field are located near the bottom of diaphragm wall.For the model established in this paper,generally,the maximum average displacement of particle located in the area which is at 0.1m distance from the bottom of diaphragm wall along the Y-axis of the outlet surface,while it is gradually stable around 0.5 ~ 0.6m.Therefore,attention should be paid to the displacement of strata near the diaphragm wall during the process of underwater excavation.The thickness between the bottom of the diaphragm wall and the lower aquifuge affects the simulation results.According to the simulation results in this paper,the larger the thickness between the bottom of the diaphragm wall and the lower aquifuge,the larger the numerical value of particle displacement will be.Generally,the velocity of the flow field increases with the increase of the thickness between the bottom of the diaphragm wall and the lower aquifuge,but opposite near the bottom of the diaphragm wall.Therefore,when choosing this parameter,the increase of the thickness between the bottom of the diaphragm wall and the lower aquifuge should be fully considered.