Strength and strain quantities under brittle compression process of hard rocks

Purpose. To examine the relationships between strength properties and strain quantities associated with the brittle compression process of hard brittle rocks. Methods. The data used in this paper were obtained from laboratory uniaxial compression tests carried out on 84 different types of hard rocks in accordance with Ulusay (2015) proposed standards. The strength properties and the strain quantities were coordinated so that each of the strain quantities or their ratios is compared individually with the strength properties of the rocks as for their relationship. Findings. In all the cases the relationships between the strain ratios and the strength parameters are stronger than when compared with individual strain quantities. A threshold level for strain ratio Ɛvf /Ɛcd may be assumed as the limit for fracture initiation above which the rock may experience brittle fracture failure. Originality. Scientific sources demonstrate few laboratory studies as for strength properties-strain quantities ratio. Most of the published research has been concentrated on crack damage stress (σcd) and uniaxial compressive strength (σc) of characteristic stress levels during compression. The paper has performed detailed analysis of the problem using experimental results of the relationships between strength properties and strain quantities under the deformation process of hard rocks. Practical implications. The relationships can improve our knowledge to evaluate correctly the stability of excavations, design of stable structures such as tunnels and excavations for mining and civil engineering purposes.