Effect of discontinuities on the survival probability of spherical blocks upon impact

The fragmentation of rocks upon impact is a complex and not well-understood phenomenon. To model this fragmentation accurately, the first question to address is whether a falling block will fragment upon impact. This can be determined if the survival probability of the rock, i.e. the probability that the rock block does not fragment, is known. However, predicting this probability is challenging, as no existing model or method can accurately forecast the survival probability of natural rocks. Recently, the authors have developed a model that can predict the survival probability of brittle rocks under collinear impact, building on a preliminary breakthrough for brittle spheres. However, natural blocks may contain discontinuities, which can increase the probability of fragmentation occurring not only due to breakage but also due to the disaggregation of the rocks along these discontinuities. The present work introduces an experimental campaign in which fully persistent and filled discontinuities were inserted into mortar spheres. The angle of the discontinuities with respect to the impact surface, as well as the impact velocity, was varied to obtain an experimental survival probability for blocks with discontinuities. The results were compared with the survival probability of intact blocks, showing how the discontinuities significantly reduce the range of energy required to break the spherical block.