Abstract
The effects of roughness and normal stress on hydraulic properties of fractures are significant during the coupled shear flow test. Knowing the laws of fluid flow and solute transport in fractures is essential to ensure the nature and safety of geological projects. Although many experiments and numerical simulations of coupled shear flow test have been conducted, there is still a lack of research on using the full Navier-Stokes (N-S) equation to solve the real flow characteristics of fluid in three-dimensional rough fractures. The main purpose of this paper is to study the influence of roughness and normal stress on the fluid flow and solute transport through fractures under the constant normal stiffness boundary condition. Based on the corrected successive random addition (SRA) algorithm, fracture surfaces with different roughness expressed by the Hurst coefficient ( H ) were generated. By applying a shear displacement of 5 mm, the sheared fracture models with normal stresses of 1 MPa, 3 MPa, and 5 MPa were obtained, respectively. The hydraulic characteristics of three-dimensional fractures were analyzed by solving the full N-S equation. The particle tracking method was employed to obtain the breakthrough curves based on the calculated flow field. The numerical method was verified with experimental results. It has been found that, for the same normal stress, the smaller the fracture H value is (i.e., more tough the fracture is), the larger the mechanical aperture is. The ratio of hydraulic aperture to mechanical aperture ( e h / e m ) decreases with the increasing of normal stress. The smaller the H value, the effect of the normal stress on the ratio e h / e m is more significant. The variation of transmissivity of fractures with the flow rate exhibits similar manner with that of e h / e m . With the normal stress and H value increasing, the mean velocity of particles becomes higher and more particles move to the outlet boundary. The dispersive transport behavior becomes obvious when normal stress is larger.
Highlights
In some rock masses with low permeability, fractures are the main channels for fluid flow
The fracture surface of the natural rock mass is generally rough [1], causing the rock fractures to be composed of void spaces and contact areas, rather than many studies assumed that fractures are composed of two relatively smooth parallel plates
It has been demonstrated that the fluid flow and transportation process in a single fracture are heavily influenced by the roughness of the fracture surface, and the mechanical aperture of a rock fracture is usually larger than its hydraulic
Summary
In some rock masses with low permeability, fractures are the main channels for fluid flow. The characteristics of void space geometry and the contact area distribution have significant effects on the hydraulic properties of a fracture [1]. It has been demonstrated that the fluid flow and transportation process in a single fracture are heavily influenced by the roughness of the fracture surface, and the mechanical aperture of a rock fracture is usually larger than its hydraulic. Li et al [3] implemented a series of coupled shear flow tests to analyze the influence of geometric features of fracture on rock mechanical behavior and proposed the empirical correlations to evaluate the effects of surface roughness and contact area on the behavior of fluid flow through rough fractures. A number of numerical simulations by solving the full 3D Navier-Stokes equations were adopted to investigate the fluid flow behavior and solute transportation through fractures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
