Three-Dimensional Numerical Investigation of Coupled Flow-Stress-Damage Failure Process in Heterogeneous Poroelastic Rocks

Abstract

The failure mechanism of heterogeneous rocks (geological materials), especially under hydraulic conditions, is important in geological engineering. The coupled mechanism of flow-stress-damage should be determined for the stability of rock mass engineering under triaxial stress states. Based on poroelasticity and damage theory, a three-dimensional coupled model of the flow-stress-damage failure process is studied, focusing mainly on the coupled characteristics of permeability evolution and damage in nonhomogeneous rocks. The influences of numerous mesoscale mechanical and hydraulic properties, including homogeneity, residual strength coefficient, loading rates, and strength criteria, on the macro mechanical response are analyzed. Results reveal that the stress sensitive factor and damage coefficient are key variables for controlling the progress of permeability evolution, and these can reflect the hydraulic properties under pre-peak and post-peak separately. Moreover, several experiments are conducted to evaluate the method in terms of permeability evolution and failure process and to verify the proposed two-stage permeability evolution model. This model can be used to illustrate the failure mechanics under hydraulic conditions and match different rock types. The relation of permeability with strain can also help confirm appropriate rock mass hydraulic parameters, thereby enhancing our understanding of the coupled failure mechanism in rock mass engineering.

A Coupled Gas Flow-Mechanical Damage Model and Its Numerical Simulations on High Energy Gas Fracturing

“…As illustrated in Figure 1, the elastic damage-based constitutive law is used to evaluate the mesomechanical damage of elements with the maximum tensile stress criterion for tensile damage and the Mohr-Coulomb criterion for shear damage. The criteria can be expressed as [30][31][32][33][34][35]…”

“…The impact of elements damage on mesomechanical parameters is also considered. The elastic modulus and strength of a mesoelement degrade monotonically as damage evolves and can be expressed as [30][31][32][33][34][35]…”

“…The macromechanical parameters of shale reported by Hou et al [6] with an elastic modulus of 17 GPa, uniaxial compressive strength (UCS) of 107 MPa, tensile strength of 10 MPa, and Poisson's ratio of 0.32 are chosen in this study. In addition, a Weibull distribution as defined in the following probability density function is used here to characterize the heterogeneity of shale [30][31][32][33][34][35]:…”

“…where m is the homogeneity index reflecting the homogeneity degree of shale, c 0 is the scale parameter related to the average value of the mechanical parameter (for example, tensile strength), and c is the mesomechanical parameter of each mesoscopic element in the numerical model. More detailed description about this function can be referred in [30][31][32][33][34][35]. For a numerical sample (50 mm wide and 100 mm high) with mesomechanical parameters listed in Table 1, its elastic modulus evolution and complete stress-strain curve under uniaxial compressive condition is shown in Figures 3 and 4, respectively.…”