Numerical Research of Fluid Flow and Solute Transport in Rough Fractures under Different Normal Stress

الملخص EN

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 (eh/em) decreases with the increasing of normal stress.

The smaller the H value, the effect of the normal stress on the ratio eh/em is more significant.

The variation of transmissivity of fractures with the flow rate exhibits similar manner with that of eh/em.

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.