Effects of length-to-diameter ratio on energy storage characteristics of rock materials under uniaxial compression

This study aims to investigate the influence of length-to-diameter (L/D) ratio on the strain energy storage and evolution characteristics of rock materials during progressive rock failure under compression. Uniaxial compression tests and singlecycle loading-unloading uniaxial compression tests were conducted on four rock materials with two specimen L/D ratios. The uniaxial compressive strength (UCS) and peak strain of the rock specimens with L/D =1 were significantly greater than those of the specimens with L/D = 2, thus exhibiting a strong size effect. In the single-cycle loading-unloading uniaxial compression tests, the total energy density, elastic energy density and dissipated energy density of the specimens with different L/D ratios increased nonlinearly with the actual stress level. The specimen L/D ratio had a significant impact on the nonlinear energy evolutions over various actual stress levels. Interestingly, regardless of the L/D ratio, failure pattern and type of material in the tests, highly linear relationships exist between the elastic energy, dissipated energy and total energy. Although the UCS is sensitive to the specimen L/D ratio, the energy storage coefficient (ESC) and energy dissipation coefficient (EDC) almost show a size-independent behaviour. The ESC and EDC are not affected by the L/D ratio and failure mode and can be used as physical parameters in geotechnical engineering design.