A Laboratory-Testing-Based Study on the Strength, Deformability, and Dilatancy of Carbonate Rocks at Low Confinement

Abstract

A servo-controlled testing setup was used to investigate the stress–strain behaviour of three carbonate rocks into the post-failure region. A series of uniaxial and triaxial tests on Indiana limestone, Carrara marble, and Toral de Los Vados limestone have been performed, gathering information on the evolution of the strength parameters and stiffness of these rocks, as well as on their post-yield dilatational properties. The Carrara marble was found to be extremely ductile, even under uniaxial conditions, whereas the Indiana limestone and Toral de Los Vados limestone were more brittle. The Indiana limestone, which was the weakest rock tested, showed a notable transition to more ductile failure modes, even at modest confinements on the order of 10 MPa; this transition was reflected in the volumetric strain evolution of the rock in the form of a transition of the dilation angle towards lower, less variable values. All of the rocks tested were found to be consistent with a cohesion-weakening-friction-strengthening model for yield, with the peak friction angle of both the Carrara marble and Indiana limestone being attained after peak strength. The evolution of stiffness was also considered as a function of accumulated plastic strain. Each rock decreased in stiffness significantly following the onset of yield, and eventually reached a near-constant residual stiffness on the order of 50 % of the initial elastic stiffness.