The Influence Of The Boundary Effect On The Seepage And Its Correction Method In Homogeneous Porous Medium Experiment

In recent 20 years,the study of media heterogeneity had attracted people's attention,and made great progress.Many researchers had been concerned on the theoretical study of boundary effect in fractured media,while the boundary effect in the homogeneous porous medium had not attracted enough attention.It is of great importance to study the nonuniform seepage under the influence of the wall effect in the porous medium.This paper based on the project of National Natural Science Foundation of China.The effect of the boundary effect in the homogeneous pore media under different rough edges of the wall was studied by systematic laboratory experiment.The quantitative correction equation of boundary effect seepage flow velocity was established,based on the combination of numerical simulation and statistical analysis.The research results of this paper are as follows:1.In the homogeneous porous medium experiment,the boundary effect was existed under different side wall roughness conditions.Under different rough edges,the effect of boundary effect on seepage was different.In this experiment,three experimental schemes were set up from the perspective of side wall conditions which affect non-uniform seepage that were the smooth organic glass plate wall,the rough edge wall of 0.3mm and the rough edge wall of 0.7mm.The influence of the roughness of the wall in the homogeneous porous medium could be found by analyzing the three different schemes.Under different wall roughness,there were non-uniform seepage phenomena in which the solute transport near the side wall was faster than the middle main flow moved upwards.The concentration on both sides of the same section was higher than the middle main stream upward concentration value.Under the same medium and hydraulic gradient condition,the more rough edge conditions,the longer the seepage time,and the more obvious non-uniform seepage.2.According to the experimental results,the nonuniform distribution characteristics of seepage velocity were determined by theoretical analysis method,and then the spatial heterogeneity of permeability coefficient was determined.The flow velocity of the observation points in the experiment was difficult to be measured,so the velocity of each space point was determined by the tracer concentration field.The real-time conductivity of the Cl-was obtained by online monitoring device.The conductivity value was converted into concentration value according to the relationship between the concentration and the conductance value.The parameters such as actual flow rate,Darcy velocity,permeability coefficient were calculated according to the change of the peak concentration.The seepage characteristic value was the basis for establishing the seepage flow velocity correction equation under the influence of boundary effect.3.The velocity correction equation was solved by means of numerical simulation and statistical analysis.The Feflow software was used to establish the percolation numerical model system,which was in accordance with the experimental conditions.Adjusted and determined the spatial heterogeneity distribution of the permeability coefficient values according to the experiment,by comparing the concentration field of the numerical simulation with the actual concentration field of the experimental observation data.Then the spatial nonuniform distribution of the corrected seepage velocity was solved by Darcy's law.Then,the seepage velocity correction equation was solved combined with the SPSS statistical analysis method.4.The temporal and spatial evolution characteristics of the concentration field under the influence of the boundary effect are predicted and analyzed,according to the convective dispersion equation of the coupled seepage correction equation.The seepage correction equation was established by coupled to establish the seepage correction equation.The spatial distribution of the tracer concentration at different times was simulated.Compared with the observed pore concentration distribution,the correctness of the established seepage flow rate correction equation was verified.Calculated the difference between the actual flow rate and the theoretical flow rate,and plotted the contour of the difference of velocity and analysis the characteristics of the non-uniform flow.5.The quantitative effect of the boundary effect on seepage flow could be used for the reference.In this paper,the seepage flow in the homogeneous porous medium was analyzed by means of theoretical analysis,numerical simulation and statistical analysis.The seepage velocity correction was established,under the influence of different boundary effect.The research idea and the method provided the reference for the study of indoor nonuniform seepage.