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Strong anisotropy of tensile behaviros and spatial anisotropic deformation have been found in transversely isotropic rock discs. There is seldom attention paid for the insightful analysis of anisotropy and spatial variability of tensile behaviours for jointed rock masses. In the paper, an index termed as the “directionality” was proposed to quantitatively assess both the directionality and spatial variability of tensile strength of jointed rock masses. Experimental Brazilian tensile tests were carried out on stratified biotite granulite rocks. Corresponding to the configurations of laboratory tests, numerical simulations of rock specimens with different joint distributions and discrete fractures network (DFN) models were then performed using PFC2D code. The results indicated that the stratified rock discs displayed distinct anisotropy and directionality in tensile strength, manifested by the decreasing strength with inclination angle. The maximum directionality of the stratified rocks measured in laboratory was 2.40/0°, which was perpendicular to the layered discontinuities, while the tensile strength determined by DFN models showed a lower anisotropy and directionality (1.38/30°). Obvious anisotropic characteristics were observed in the fracture patterns of failure in DFN models. This paper implies the necessity of consideirng the anisotropy and directionality for the study of failure mechanisms of surrounding rocks in underground tunnels. [ABSTRACT FROM AUTHOR]

Anisotropy is one of the most distinct features of stratified rock mass and it must be considered in engineering design and stability analysis. On the basis of linear elastic theory and displacements equivalence, a computational model considering elastic anisotropy was established. The equivalent elastic modulus and equivalent Poisson's ratio of the stratified rock perpendicular and parallel to the loading direction were discussed. The relations of material properties and geometry parameters with the equivalent elastic modulus and equivalent Poisson's ratio in two directions were studied. Uniaxial compressive test was conducted and the elastic modulus and Poisson's ratio in the proposed model agreed well with experimental results. The comparison between a comprehensive set of experimental data and theoretical analysis data proves that the proposed constitutive model can effectively characteristic the mechanical behavior of stratified rocks. The proposed model can consider the effects of material parameters and geometry parameters of rock and joints on the mechanical behavior of stratified rock mass. Moreover, the elastic anisotropy was considered in the model. Thus, the model can supply some valuable reference in studying deformation of stratified rock mass and engineering design. [ABSTRACT FROM AUTHOR]

• Fractal joint network quantitatively evaluating the joint roughness was proposed. • An index termed as directionality for surrounding rock of tunnels was proposed. • Peak strength anisotropy and directionality of jointed rock mass were evaluated. • Clear linear correlation between rock strength and excavation sizes was obtained. The influence of the fractures on the anisotropic mechanical behavior of excavated fractured rock mass is important for the stability of rock tunnels. Rough joints were generated using fractal principles, and the Monte Carlo method was employed to create joint network faces. Biaxial compression numerical simulations were conducted using the discrete element method to analyze the behavior of the rock mass containing these networks. Quantitative analysis was carried out to evaluate the strength variability and total number of cracks in the jointed rock mass. A linear regression analysis was conducted to establish the relationship between rock strength and excavation size. The findings demonstrate significant disparities between the linear and fractal models regarding rock damage mode, stress–strain curves, and crack evolution patterns. Tensile rupture and local shear damage were found to be the primary fracture modes for the fractured rock tunnels, forming a V-shaped damage zone within the central tunnel. The shape of this zone was influenced by fracture direction and excavation ratio. Excavation at the center of the rock mass substantially impacted the variability of rock strength and the occurrence of internal cracks. An increase in the slope ratio led to a greater variability of rock mass strength, transitioning from nearly isotropic to weakly anisotropic behavior. The total number of cracks exhibited a W-shaped trend, initially increasing and later decreasing as the slope ratio decreased. Additionally, a clear linear correlation was observed between rock strength and excavation ratio at the center of the rock mass. [ABSTRACT FROM AUTHOR]

The characteristics of the anisotropy and directionality of jointed rock masses are the key to simplifying it as a transversely anisotropic material. Experimental direct shear tests were performed on stratified rocks cored from granulite rocks. The influence of normal stresses and joint orientations was tested and the anisotropy and directionality of the shear strength were evaluated. Numerical shearing tests on stratified rock models and discrete fractures network (DFN) models were subsequently conducted. In addition, the shear anisotropy and directionality in the DFN models were tested and discussed. The results demonstrate that the peak shear stress was more sensitive to the inclination angles than the normal stress. The stratified rocks in the experimental test showed apparent shear anisotropy and directionality. The maximum value of directionality coincided with the direction of the strike of the bedding plane. The more apparent the anisotropy was, the higher the directionality became. The failure patterns of stratified rocks exhibited more complex characteristics under higher normal stress. Significant variation of the shear strength distribution occurred due to the different orientations of fractures relative to the directions of the shear load. The failure patterns of DFN models of varied scales differed, and no apparent convergence was discovered. The shear strength of the DFN model showed an apparent principal direction. The numerical results presented in this paper are valuable for evaluating the prediction of the failure behaviour of rock masses, and can be further applied to the study of the failure mechanism of surrounding rock in engineering. [ABSTRACT FROM AUTHOR]