Gravity-induced collapse of a soft rock cliff due to notch growth

Cliff erosion is an unstoppable natural process increasingly occurring due to climate change and frequently causing crucial georisks on rocky coasts throughout the world. The resilience of a cliff depends on a variety of environmental, geometrical, geological and geotechnical conditions that have been included in several heuristic coastal hazard assessment approaches. In order to provide new quantitative insights into the relationship between some geometrical and structural characteristics of a sea cliff (height, basal erosion, discontinuities) and its stability conditions (failure mechanism, safety factor), this paper investigates numerically how the progressive undermining of a soft rock cliff affects its mechanical behaviour. It has been found that the undermining depth plays a significant role on cliff stability, whose mechanism of collapse changes according to the overhang slenderness. When a vertical joint is present, the higher the persistence, the lower the global safety factor. Moreover, as the joint moves away from the cliff face, the safety factor decreases, the worse condition being found when it is above the notch end. The results obtained can contribute to a deeper understanding of the failure mechanisms of sea cliffs, helping in a reliable assessment of coastal risk and a proper design of the mitigation measures.