Study On Determining The Permeability Tensor Of Fractured Rock Mass By One-dimensional Ring Element Model

Rock mass fissures are ubiquitous in rock mass engineering,especially in related fields such as petroleum engineering,nuclear power engineering,waste storage and mineral resources exploitation,as well as major water conservancy and hydropower projects,civil engineering and so on.The mechanical characteristics such as groundwater permeability directly affect the design,construction,operation and maintenance of various rock mass engineering.Therefore,it is very important to study the permeability law of fractured rock mass,and the indirect method to solve the seepage problem of actual engineering is studying the permeability tensor of the rock mass,and the permeability tensor is an important physical quantity for seepage analysis.With the development of eomputer technology,it is widely used to determine the permeability characteristics of rock mass by computer simulation technology.Combined with field test comparison and correction,the permeability tensor reflecting the anisotropy of rock mass is obtained at the macro level.This method is widely used.At present,there are relatively systematic understandings of the properties and seepage systems of fractured rock masses at home and abroad,but there are only two kinds of calculation models:tubular flow model and planar flow model.The tube flow model has been studied by many scholars.The planar flow model is less studied by scholars because of the complexity of mesh division and large computational complexity.In this paper,based on the planar flow model,a spatial one-dimensional ring element is proposed to simplify the calculation.The expression of the permeability tensor can be accurately calculated.The model can also be directly used in the calculation of the fracture network,which makes the calculation scale become a reality.In addition,this article also studied the following:(1)According to the crack statistics parameters of the site survey,the Baecher model was selected,and the three-dimensional random fracture network was used to simulate the rock mass fracture network model based on the Monte-Carlo method.Starting from the calculation principle of permeation tensor,the first-dimensional one-dimensional ring element model for three-dimensional fracture network seepage calculation is proposed.The calculation function of the program is used to directly obtain the diameter of the ring element and perform the seepage calculation.(2)According to the permeation tensor obtained by the computer,the penetration ellipsoid is fitted.The generation of the osmotic spheroid can visually judge whether the permeation tensor calculated by the ring unit is correct or not,and can also provide a graphical verification for the calculation of the subsequent REV method.(3)At the end of the paper,the size of REV is estimated.As the size of the fractured rock specimen increases,the equivalent permeability tensor of the fractured rock mass gradually becomes stable,and the REV of the rock mass considered is finally determined to be 26m×26m×26m.