Abstract
Abstract. Plane failure along inclined joints is a classical mechanism involved in rock slope movements. It is known that the number, size and position of rock bridges along the potential failure plane are of prime importance when assessing slope stability. However, the rock bridge failure phenomenology itself has not been comprehensively understood up to now. In this study, the propagation cascade effect of rock bridge failure leading to catastrophic block sliding is studied and the influence of rock bridge position in regard to the rockfall failure mode (shear or tension) is highlighted. Numerical modelling using the distinct element method (UDEC, Itasca) is undertaken in order to assess the stability of a 10 m3 rock block lying on an inclined joint with a dip angle of 40 or 80∘. The progressive failure of rock bridges is simulated assuming a Mohr–Coulomb failure criterion and considering stress transfers from a failed bridge to the surrounding ones. Two phases of the failure process are described: (1) a stable propagation of the rock bridge failures along the joint and (2) an unstable propagation (cascade effect) of rock bridge failures until the block slides down. Additionally, the most critical position of rock bridges has been identified. It corresponds to the top of the rock block for a dip angle of 40∘ and to its bottom for an angle of 80∘.
Highlights
Rockfall hazard is defined as “the probability of occurrence of a potentially damaging rockfall within a given area and in a given period of time” (Varnes, 1984)
To study the phenomenology of rock bridge failure (RB and rock bridge failed (RBF)), the evolution of normal and shear stresses along the joint during the stepwise introduction of open-crack (OC) contacts has been analysed in detail
The distribution of the stresses along the rock joint is presented at Step 0, considering that the joint is only composed of rock bridges
Summary
Rockfall hazard is defined as “the probability of occurrence of a potentially damaging rockfall within a given area and in a given period of time” (Varnes, 1984). The damaging phenomenon generally results from the failure of weakness planes and the fall of one or several rock blocks down to the target area (Corominas et al, 2005). The rockfall hazard can be defined as the failure probability multiplied by the probability of propagation. While different probabilistic methods exist to calculate the probability of propagation (Guzzetti et al, 2002; Jaboyedoff et al, 2005; Bourrier et al, 2009; Levy et al, 2018), the failure probability is more complex to assess. The understanding of the failure process of weakness planes is a major issue for risk assessment as it is responsible for the generation of a rockfall and defines its time of occurrence
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