ABSTRACT

Based on mesoscopic damage mechanics, numerical codes RFPA2D is developed to simulate the Complete failure process of seven transversely isotropic rock samples subjected to uniaxial loading. The rock samples are composed of two different rock materials and they are formed with different dip angles between the rock layer orientation and the loading direction. Complete stress-strain curves are obtained and the deformability and failure behaviors are described. Numerical results show rock layer dip angle of transversely isotropic rocks has significant influence on the fracture during the progressive failure process, such as peak strength, failure manners, and deformational behavior et al. It is suitable to apply different failure criteria according to different failure modes caused by layer dip angle.

INTRODUCTION

Many types of rocks such as sedimentary rocks and metamorphic rocks containing fabric with preferentially parallel arrangements of flat or long minerals may be transversely isotropic. Isotropic rocks cut by regular discontinuities may also exhibit obvious trans- Versely isotropic properties, such as granite and basalt (Wittke 1990). In civil and mining engineering, such as In the analysis of stability of slope, underground excavation and boreholes for mining, many failures results from the anisotropy can be found. The mechanics properties of transversely isotropic rocks are the same along any orientations on one plan and different on the perpendicular plan. Significant errors may occur if anisotropic rocks are treated as isotropic rocks. In the last several decades, considerable efforts are made on the study of anisotropic rocks, from both experimental and theoretical points of view (Donath 1964; Borecki et al 1981; Brady & Brown 1993; Hoek 1964' Jaeger 196 0; Duveau & Shao 1998; Cazacu et al 1998).

Many scholars have developed failure criteria for the transversely Isotropic rocks to get variation of rock mechanics properties with the orientation angles under various confining pressures. Jaeger (1960) introduced a basic analysis on rocks containing well-defined, parallel discontinuity. He considered that if the rock failure does not occurred along the discontinuity, the rock can be treated as isotropic rocks. Duveau & Shao (1998) provided modification by replacing the Mohr-Coulomb criterion with a non-linear model to express the strength along the discontinuity. The strength criteria for the transversely isotropic rocks developed by McLamore & Gray (1967), Hoek & Brown (1964) and Ramarnurthy (1993) generally provide fairly accurate simulation of the experimental data. A more general criterion was proposed by Hill (1950) based on Mises's isotropic criterion. Pariseau (1972) and Cazacu (1998) et al. extended Hill's criterion to account for the effect of the hydrostatic stresses. As pointed out by Tian (2001), both of their criteria describe the continuous variation of strength with the orientation angle, which is referred to herein as the continuous model and the continuous model is not suitable for the shoulder and undulatory type of rocks.

Though a lot of constitutive laws and failure criteria have been proposed based on experimental results, the parameters used in the theoretical models, have considerable dependence on the experimental results.

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