Experimental Study on the Shear-Flow Coupled Behavior of Tension Fractures Under Constant Normal Stiffness Boundary Conditions

Abstract

This study experimentally investigated the effects of fracture surface roughness, normal stiffness, and initial normal stress on the shear-flow behavior of rough-walled rock fractures. A series of shear-flow tests were performed on two rough fractures, under various constant normal stiffness (CNS) boundary conditions. The results showed that the CNS boundary conditions have a significant influence on the mechanical and hydraulic behaviors of fractures, during shearing. The peak shear stress shows an increasing trend with the increases in the initial normal stress and fracture roughness. The residual shear stress increases with increasing the surface roughness, normal stiffness, and initial normal stress. The dilation of fracture is restrained more significantly under high normal stiffness and initial normal stress conditions. The hydraulic tests show that the evolutions of transmissivity and hydraulic aperture exhibit a three-stage behavior, during the shear process—a slight decrease stage due to the shear contraction, a fast growth stage due to shear dilation, and a slow growth stage due to the reduction rate of the mechanical aperture increment. The transmissivity and hydraulic aperture decreased, gradually, as the normal stiffness and initial normal stress increase.

Controls on the intrinsic flow properties of mudrock fractures: A review of their importance in subsurface storage

“…Ultimately, increasing shear displacement increases both the mean and standard deviation of the aperture (i.e. alteration in the relative roughness) (Frash et al, 2017;Wang et al, 2019;Yeo et al, 1998). Additionally, enhanced void space nucleation through aperture dilation has been shown to form channels aligning perpendicular to the shear direction, altering permeability by up to two orders of magnitude (Council et al, 1996;Esaki et al, 1991;Gale, 1990;Liu et al, 2020;Yeo et al, 1998).…”

Experimental investigation on nonlinear flow properties of fluids through rough-walled shale fractures after shear

“…Rong et al (2018) presented an improved ow model for calculating nonlinear ow behaviors in rock fractures during shear, and the linear and nonlinear coe cients in the Forchheimer equation were determined by mechanical aperture and fracture roughness coe cients. Wang et al (2019) experimentally investigated the effects of fracture surface roughness, normal stiffness, and initial normal stress on the shear-ow behavior of rough-walled rock fractures. Chen et al (2021) proposed a simpli ed modeling algorithm to quantitatively characterize the asperity degradation and gouge accumulation within the fracture during shear, based on which a series of numerical simulations were conducted to analyze the link between fracture geometries and ow behaviors during shear.…”

Effect of joint roughness coefficient and size on shear and characteristic strengths of structural planes

“…Scholars have used shear flow tests to study the influence of the JRC on shear strength. For example, Wang et al [ 13 ] conducted a shear flow test on two rough cracks to study the effect of fracture plane roughness on the shear of rough wall rock cracks. Scholars have studied the relationship between the JRC and shear strength based on field tests.…”