A theoretical model for the effect of porosity on the relation between uniaxial compressive strength of rocks and point load index

Point load test (PLT) is one of the most adopted indirect ways to estimate uniaxial compressive strength of rocks. Yet, the estimation can be interfered by rock porosity that has rarely been considered in model development. In this study, a theoretical model for the interpretation of results of PLTs considering the effect of porosity is proposed. The model was developed using the elastic stress field inside diametrically loaded sphere within the framework of linear elastic fracture mechanics and requires only basic physical parameters including porosity and Poisson's ratio. Apart from the point load index (PLI), an extra parameter, subtended angle, is included in the interpretation, which accounts partly for the wide range of the ratio between PLI and uniaxial compressive strength observed in experiments. The predictions of the proposed model compare reasonably well with data for a variety of rocks, which demonstrates the validity of the model.