This study introduces a new hydromechanical model to estimate both shear and nonlinear flow behaviours of a single rock fracture, taking into account the effects of fracture surface morphology on the fracture flow behaviours. The model incorporates a multi-scale roughness shear constitutive model that considers the adhesion and abrasion wear theories to predict the shear behaviours of a fracture due to shear deformations. The fracture permeability is estimated using the Forchheimer-based equation, which accounts for the combined effects of the fracture void spaces, aperture distributions, and fluid flow tortuosity. Laboratory shear-flow experiments under different hydraulic pressures and normal loading conditions are conducted to validate the proposed model. The model is in good agreement with experimental data and can be applied to sheared aquifers.
Fluid flow through rock fracture is a crucial issue in seepage-related engineering projects and has been extensively studied over a few decades (Olsson and Barton, 2001, Xiong et al., 2011, Rong et al., 2018, Wang et al., 2020). One of the simplest conceptual models to estimate fracture permeability is the cubic law, which assumes that the fracture consists of two smooth and parallel plates. This model is valid for low flow rate conditions and states that the fracture flow rate is proportional to the cube of the fracture aperture, as proposed by Witherspoon et al. (1980).
In a shear process, the evolutions of fracture surface morphology result in the occurrence of nonlinear flow. Experimental observations show that the linear cubic law deviates from the nonlinear flow behaviours with increasing applied water pressures and inhomogeneity of surface geometries (Rong et al., 2018). However, only a few models have been developed to estimate shear-flow behaviours of a fracture. Olsson and Barton (2001) estimated shear behaviour using the Barton-Bandis shear model and hydraulic behaviour using modified cubic law. Later, Rong et al. (2018) extended this model to solve the nonlinear fracture flow by a Forchheimer-based equation. However, determining a unique JRC value on an irregular fracture is difficult. Besides, a single JRC or JRCmob cannot explain the influences of complex surface morphology, e.g., various aperture, contact distributions, and flow tortuosity, on fracture flow behaviours. Xiong et al. (2011) developed a flow model to predict the fracture hydraulic properties during shearing. They proposed an empirical equation between mechanical aperture em and hydraulic aperture eh by considering the mean and standard deviations of the local apertures, which were estimated by a fracture void space model. However, the fluid flow governing equation is the cubic law, which has limitations in solving nonlinear fracture flow problems.
