Abstract

In mining operations, rocks are subjected to dynamic loading due to moving vehicles, material loading, drilling-blasting, and mechanical excavations. Therefore, rocks fail prematurely because of the repeated loading-unloading cycles. Variations in the ultimate strength of rocks result in experimental tests difficult to investigate the effect of cyclic loading on rock fatigue behavior. On the other hand, numerical modelling is a feasible option to simulate rock fatigue damage. We simulated rock fatigue damage in three-dimensional finite element analysis (FEA) and introduced a new damage assessment model. Comparison of the results with laboratory test results verified that new damage assessment model is capable of capturing fatigue damage. Based on results from the series of parametric study, it was shown that as maximum loads increase, rock material tends to have shorter fatigue life and is more likely to fail prematurely. Besides, larger amplitudes could lead to shorter fatigue life and earlier rock failure.

1 Introduction

Mining is widely accepted as one of the most risky industries (NSW Government 2009). A large variety of potential risks can be observed in mining operations and rock fatigue damage is the most dominant cause (Mortazavi & Molladavoodi 2012) of rock failures. Therefore, rock fatigue behavior has become a major concern for most mining practices and its understanding is necessary to improve safety in the mining environment.

It is understood that rock fatigue behaviour differs under various loading conditions (Stavrogin & Tarasov 2001). In this research, the effect of cyclic loading on rock fatigue behaviour is focused on for two reasons. Firstly, the fatigue behaviour of rock materials subjected to cyclic loading is more significant and complicated than that of static loading (Dehmoobed-Sharifabadi & Joseph 2010). Secondly, cyclic loading best represents the stress on rock materials in mining situations which is mainly caused by mining excavations and large mobile mining equipment (Joseph & Dehmoobed-Sharifabadi 2007).

This research investigates rock fatigue behavior under various cyclic loading conditions of different amplitudes and maximum loads. A progressive damage model was constructed in order to observe the effects of cyclic loading characters on the rock fatigue behavior in the three-dimensional finite element analysis (FEA). To verify the simulation model, results were compared to those obtained from experimental tests, in which the material properties and scenarios of both the simulation and the laboratory experiments were identical.

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