Strength, deformation and cracking characteristics of limestones

The geomechanical properties of limestones often show substantial variations which are associated with differences in the constituents and structure of the limestone. In this study variations of geomechanical properties of limestones with varying micro-textural properties are investigated. Unconfined compressive strength tests (UCS) on limestone specimens were performed to determine the peak strength and crack initiation threshold. Additionally, the deformation characteristics were determined. Mineralogical analyses including X-Ray Diffraction were performed on each specimen. Micro-textural variations were investigated with thin sections of each tested specimen before and after mechanical perturbation. The thin section analysis was focused on determining the orientation and distribution of micro- and macro-cracks that formed during compressive loading.. Data obtained from mechanical tests reveal that the UCS values for the studied limestones varies between 38-140 MPa, and cracks are initiated at stress levels between 0.30-0.50 of the UCS. It is exposed that the peak strength, crack initiation and elastic constants are strongly influenced by the heterogeneous micro-fabric of the specimens. The existence of graphite veins, fossil fragments and calcite veins makes substantial changes in UCS, crack initiation stress levels, elastic constants and substantially affects crack propagation during compressive loading.