Evaluation of volumetric strain quantities and types of volumetric strain curves under failure-deformation process of hard brittle rocks

Purpose. The aim of this work is to show whether or not a relationship exist among the different volumetric strain quantities and to assess also whether the volumetric quantities are related to the different types of volumetric strain curves under failure-deformation process of hard brittle rocks. Methods. Tests were conducted to determine the post failure stress-strain curves of different 83 rocks types under uniaxial compression using a closed loop servo-controlled testing system in accordance to ISRM (International Society for Rock Mechanics) suggested standards. Findings. The result show that the volumetric strains quantities are related by power form law. It was established that there is a connection between the volumetric strains quantities and the types of the volumetric strains curves. The first type volumetric strain curves contains the Class I and progress to Class II while the type three volumetric strain curves are entirely Class II rock. Originality. No experimental results have been published, which describe the connection between the type of volumetric strain curves and volumetric strain quantities or attempt to relate the volumetric strain quantities with type of post-failure stress-strain characteristic curves response of rocks under uniaxial compression. Most researchers in rock mechanics studies have so far been focused on the crack damage stress (σcd) and uniaxial compressive strength (σc) of characteristic stress levels during compression in which σcd = Ɛcd and σcd = σc to study deformation behavior of rocks. Practical implications. It was also observed that the difficulty in obtaining the post-failure curves increases from type one to type two and type three volumetric strain curves respectively. It could guide personnel conducting tests using closed-loop servo-controlled testing system, if dangerous situation or equipment damage could occur (especially with the third type deformation process) so that testing is performed safely. It could also be useful in understand-ding the total process of specimen deformation and estimation of the rocks brittleness (e.g. brittle for Class II and less brittle or ductile for Class I).