| The permeability of rock mass varies with the size of the sample.The exploration of the rule and mechanism of the size effect of rock mass permeability is an engineering scale application of the results of laboratory experiments on small size,which has important scientific significance and practical value.Rock mass consists of rock blocks and fracture network mainly,and the fracture network is the main channel for seepage in rock mass,while the single fracture is the basic element of the rock mass fracture network.Therefore,the key in analyzing the size effect of seepage of rock mass is that the size effect of seepage in the single fracture should be researched.In order to study the size effect of single fracture seepage,based on three kinds of rock fracture surfaces with different roughness,the rough single fracture is reconstructed by 3D scanning technology.According to the distribution law of fracture aperture,a large-scale single fracture numerical model is constructed,and the size effect of single fracture seepage and its influencing factors are studied.The main research contents and conclusions are as follows:(1)Based on three rock surface of different roughness(R1,R2,R3),the scanned rock surfaces are clipped and processed by regular point cloud using softwares after scanning by three-dimensional scanner.The softwares include Polyworks,Wrap and Matlab,and calculated their roughness,respectively.And the regular point cloud is to construct a rough single fracture with a height of 0.2 mm by using the way of“lifting”and“dislocation”.The aperture distribution of the rough single fracture after construction was calculated,and the mathematical statistics of the aperture data were conducted.The results show that the three sets of aperture data basically conform to the normal distribution.meanwhile,in order to obtain the statistical data of different aperture,the“lifting”height was changed during the construction of single crack.The“lifting”height is 0.05 mm,1 mm,2 mm,a total of 9 sets of aperture statistical data,the research results show that the“lifting”height is 1 mm and 2 mm of the aperture data most obeys the normal distribution.(2)In order to explore the size effect of coarse single fracture permeability,the large-scale fracture surface with normal distribution of fracture aperture is generated by using Matlab software,which is imported into COMSOL software for modeling,and the rough single fracture is constructed by“lifting”and“merging”fracture surface,and then the size effect of large-scale single fracture permeability is studied.The simulation results show that the permeability of rough single fracture increases with the increase of sample size.When the sample size reaches 14 m×14 m,the permeability coefficient no longer increases with the increase of sample size,but fluctuates around a certain value.The certain value is 5.55246×10-6m/s,so 14 m is defined as the critical size.In order to further study the influence factors of the size effect of single fracture permeability,the fracture aperture and roughness are selected as the influence factors to carry out the single fracture permeability simulation research under different fracture aperture and roughness.The results show that with the increase of the aperture,the increase of the seepage flow rate is more obvious under different aperture.The permeability coefficient increases and the critical size decreases with the increase of the aperture.With the increase of roughness,the seepage flow rate decreases under different roughness.The permeability coefficient decreases and the critical size increases with the increase of roughness. |
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