Study On Size Effect Of Permeability For A Single Rough-walled Fracture

The size effect of fractured rock mass permeability is a key issue concerning the results of indoor small-size test in engineering application.In order to study the laws of the size effect of rock mass permeability and its influencing factors,radial seepage research was conducted for a single rough-walled fracture with a series of size via an independently developed single rough-walled fracture permeability test system.In the process of test,dyeing solution was used as permeability media,and transparent organic glass was used as sample,so as to achieve visualization research.Moreover,the study of a series of size was expanded by using COMSOL,and the critical size was obtained.Meanwhile,the permeability tests of variable roughness,variable fracture width,variable normal stress and variable hydraulic gradient were performed,and the factors influencing the size effect of single rough-walled fracture permeability were studied.The specific research work in this paper was as follows:(1)First of all,large-size single rough-walled fracture sample was established by using modeling software,and numerical simulation software was imported.A consistent model was established by using organic glass.The numerical simulation verification test of single rough-walled fracture permeability was carried out by using the visualization of organic glass and the shooting of high-speed camera,so as to verify the reliability of numerical model.(2)Single rough-walled fracture model with a series of size was established via numerical simulation software.The numerical simulation test of the size effect of single rough-walled fracture permeability was conducted,and the following results were obtained: the permeability coefficient of single rough-walled fracture increased as the sample size increased,namely there had size effect,and it tended to be stable when the size is r=11m(JRC=1.476,b=2mm,r is the sample size radius).(3)The permeability test of single rough-walled fracture was conducted under the variable conditions of fracture roughness,fracture width,normal stress and hydraulic gradient,and the results showed: the roughness had an obvious influence on permeability,its permeability coefficient decreased as the roughness of single roughwalled fracture increased,and its critical size increased as the roughness increased;the fracture width of single rough-walled fracture had a significant influence on fracture permeability,the fracture permeability increased as the fracture width increased,and its critical size decreased as the fracture width increased;the normal stress had a great influence on fracture permeability,the fracture permeability decreased gradually as the normal stress increased,and its critical size increased as the normal stress increased;and the hydraulic gradient had an influence on fracture permeability,the fracture permeability increased gradually as the hydraulic gradient increased,and its critical size decreased as the hydraulic gradient increased.(4)Sensitivity analysis was performed for the factors influencing the size effect of single rough-walled fracture permeability,and the results indicated: the fracture width had the biggest influence on its critical size,followed by the normal stress,and the hydraulic gradient had the smallest influence on its critical size.