Abstract
Mechanical properties of rock masses are dominated by the nonlinear response of joints and their arrangement. In this paper, combined influences of joint spacing (s) and joint inclination angle (β) on mechanical behavior of rock mass models with large open joints under uniaxial compression were investigated by PFC modeling. With a large amount of local measurement circles placed along the pre-defined measurement lines (ML), stresses and joint response parameters at different scales (the measurement circles, the MLs and the whole specimen) were defined and calculated. It was found that macroscopic behaviors of the jointed specimens, such as four types of deformation behaviors, four failure modes, strength, deformability modulus and ductility index, are dominated by nonlinear response of the joint system, especially the interaction between the joints and rock bridges. The joints may experience three stages, i.e., starting to close, closed and opening again. On the joint plane, the peak stresses of the rock bridges and those of the joints may not be reached at the same time; i.e., joint strength mobilization happens with the loss of the rock bridges’ resistance. The influence of s on specimen behavior is little for β = 90°, obvious for β = 0° or 30° and significant for β = 45° or 60°, and this can be related to their different microscopic damage mechanisms.
Highlights
Evaluation of mechanical properties of rock masses is of great importance for safe, efficient and sustainable exploitation of underground energy resources
Figure it can be seen that: (1) at each joint spacing s, a increase with β in general while Rcj and Fnj decrease with β, and the curves of Fsj vs. β are inverted V-shaped with the maxima at β = 30◦ ; (2) for a given joint inclination angle β, a decrease with s while Rcj, Fnj and Fsj increase with s; (3) joint strength immobilized for β = 90◦ or 60◦, while slightly, moderately and significantly mobilized for β = 45◦, N
The response of joint system can be measured by evolution of the four joint response parameters, i.e., average aperture, ratio of closed number, and normalized average normal and shear forces of smooth joint (SJ) contacts in the whole specimen (a, Rcj, Fnj and Fsj )
Summary
Evaluation of mechanical properties of rock masses is of great importance for safe, efficient and sustainable exploitation of underground energy resources (coal, oil and gas, geothermal etc.). Designation) [1], RMR (Rock Mass Rating) [2], Q [3] and GSI (Geological Strength Index) [4,5]. In these rock mass classification systems, a few of the key geometrical parameters of joint network are taken into account individually, such as the number of joint sets, the joint spacing and orientation of joints relative to the structure. Based on the above-mentioned rock mass classification systems, some empirical relations have been proposed to estimate strength and deformability of jointed rock masses. Hoek and Energies 2020, 13, 6698; doi:10.3390/en13246698 www.mdpi.com/journal/energies
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