Research On Seepage Characteristics Of Complex Rock Mass Fissure Based On Lattice Boltzmann Method

Rock mass fracture seepage research plays an important role in underground engineering,such as mining engineering,nuclear scrap save engineering,underground tunnels,nuclear power plant foundation.a lot of cracks inside the rock,affected by geological action and later unloading.the existence of cracks not only affects the strength of the rock mass,but also becomes the main channel for seepage inside the rock mass,the direction of the cracks is random and uncertain in the in the rock mass,the fracture width and surface profile distribution are heterogeneity and discontinuity,according to the form,there are Connected single fractures,intersecting fractures,and even connected fracture networks within the rock mass.based on this,this article through numerical simulation generated a single fracture,intersecting fractures,and fracture network of porous media,combined with lattice Boltzmann method simulation the seepage of different fractures the research results as fallow;(1)Simulate the seepage flow of flat fracture driven by the pressure,and verify the classic Poiseuille flow by comparing the velocities in the horizontal direction.for the cubic law,consider using multi-plate equivalent model seepage flow.comparison of numerical and analytical solutions,verified the method of simulation correctness,the height of the step and the length of the crack will cause errors through analysis.(2)Comebined with the method of midpoint generation to generate single fracture model with different roughness,simulated different roughness fracture seepage under the velocity boundary condition.the analysis showed that;near the fracture wall the fluid flow is blocked by the solid raised wall,fluid flow line bending and occurs around the flow phenomenon,as the distance from the rough fracture surface increases,the degree of bending of the streamline gradually decreases.Since the fracture raised wall Obstruction the average pressure drop at adjacent points get changes,and the pressure drop changes are particularly significant in places where the fluctuations along the path change suddenly.The average pressure drop of adjacentpoints has a similar trend with the fluctuation of the surface,the average pressure drop is increasing at the raised position of the wall surface,while the concave position is showing a decrease.(3)Simulate the intersecting fractures seepage driven by the pressure drop,analyze the effect by angle,gap width and differential pressure for the loss pressure drop ratio.affected by the change of the fracture angle,flow trajectory becomes curved in the flow direction of the fracture from left to right,as the angle increases,the degree of curvature increases,and the flow is blocked,the loss pressure drop ratio increases with the increase of the fracture angle.affected by the width of the fracture Single fracture and bifurcated fracture are the flow capacity in the fracture increases,the velocity of flow increases,the loss energy at the crack corner decreases,and the loss pressure drop ratio decreases As the fracture width increases.Because of increasing the gap width along the flow direction,the cross-fracture increases its loss pressure drop ratio when increasing the gap width,while increasing the gap width along the non-flow direction increases its loss pressure drop ratio.the increasing the fracture width along its flow direction,the criss-cross fracture will reduce its loss pressure drop ratio,while increasing the fracture width along the non-flow direction will increase its loss pressure drop ratio.(4)According to the random distribution of real fractures in nature,a two-dimensional complex fracture network structure was generated using matlab software,and combined with the lattice Boltzmann method to simulate the fracture network seepage Based on the mean Thiessen polygons,as the number of points in the area increases,the flow channels in the fracture increase and the porosity increases,resulting in an increase in permeability.Due to the random distribution of fractures,The permeability increases irregularly.affected by the area distribution,as the fracture increase,the width of the fractures changes.When the number of points increases,the permeability decreases irregularly due to the changes in the fracture width.For the non-mean Thiessen polygons,as the points are concentrated in the designated area,the fracture permeability shows a downward trend.