1 Introduction

Stability and serviceability of brittle rocks or rock masses is mainly governed by load level and strength, whereby three processes can be distinguished: sub-critical crack and critical crack growth under constant or slowly changing load and dynamic triggered failure. Some selected recent research results with respect to (1.) continuum and discontinuum based numerical approaches considering subcritical and critical crack growth under constant load (Chen et al. 2014, 2015, 2016; Konietzky et al. 2009, 2015; Li et al. 2014, 2015, 2016; Tan et al. 2016) and (2.) first results of the stability of discontinuities under complex dynamic loading obtained by dynamic shear box tests (Dang et al. 2016a,b) are presented.

2 Damage evolution due to subcritical and critical crack growth

Macroscopic fracturing is considered as the result of the growth and coalescence of microcracks. Based on fracture mechanics, (based on Charles or Charles-Hillig equations) and critical crack growth (linear elastic fracture mechanics) can be distinguished and used to determine the life time of rocks under loading using stress and crack-size dependent crack propagation velocity. Exemplary, Fig. 1 shows numerical simulation of damage evolution over time in terms of failed zone counts and axial deformation of a rock sample under uniaxial compression, which reveals primary, secondary and tertiary creep phases. This model assumes the existence of a huge number of microcracks with different length and orientation following certain stochastic distributions.

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