Abstract:

An improved understanding of rock bridge failure is a significant factor in future mining and geotechnical studies, particularly as open pits increase in depth. The progressive failure of rock bridges is an important process during damage development and brittle crack propagation in rock slopes. This paper investigates the importance of pre-existing discontinuities and rock bridges at the micro scale on rock strength. Mechanisms of rock crack initiation, coalescence and propagation in rock with an emphasis on rock bridge failure are analyzed using 2D finite-discrete element (FDEM) numerical models. The scope of this study is to simulate the behaviour of a homogeneous and isotropic Barre Granite under standard laboratory uniaxial compression test. The capability of the code to accurately model the mechanical behaviour of homogeneous rock is validated against results published in the literature. In addition, new methodologies are suggested for processing the numerically-generated cracks at the laboratory-scale models. Discrete Crack Network techniques are employed to monitor crack development, locate crack nucleation sites and investigate crack coalescence and propagation associated with rock bridge failure.

Introduction

Step-path failure in rock slopes involves brittle crack initiation, propagation, coalescence and final failure. Stability analysis approaches for high natural or engineering rock slopes should account for brittle failure due to high stress concentrations that may exist leading to the development of stress-induced rock cracks (Hajiabdolmajid and Kaiser, 2002). These stress-induced cracks may provide kinematic freedom for a previously stable block and result in slope failure. The stochastic character of geometric parameters, persistence and water pressure need to be considered in various rock bridge configurations as well as computation of an overall probability of slope failure. The partially-controlled failure occurs through a combination of different mechanisms such as tensile cracking and sliding on preexisting structures in the rock mass. In these cases, development of the stress-induced cracks is required for failure as the rock mass is not kinematically free to move out of the slope. This type of failure often occurs at larger scales where high stress levels may cause the development of secondary, stress-induced damage zones.

Due to the importance of rock bridge formation in geotechnical engineering studies, the cracking stages and the rock bridge response should be investigated at the laboratory-scale. Determination of the cracking levels during crack propagation is one of the key challenges in rock mechanics.

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