End and shape effects of brittle rock under uniaxial compression

Accurate estimation of rock strength is one of the most important tasks in rock engineering design. We analyzed the mechanical and failure properties of rock specimens affected by the end and shape effects under uniaxial compression through experimental and numerical studies. It was found that the end effect could change the failure mode of rock specimens from splitting failure to shear failure, as the coefficient of friction at the rock specimen-loading platens contacts increased. When the coefficient of friction was increasing, the contour distribution of the equivalent plastic strain of specimen also changed, which simultaneously influenced by the shape of specimen. It can be observed that an increase in the slenderness of specimen caused a decrease in end frictional effect on the uniaxial compressive strength of rock specimen. The numerical results also revealed that the shape effect originated from the end frictional effect as the rock material was homogeneous. The relationship between the uniaxial compressive strength and the aspect ratio of specimen was obtained and fitted by incorporating the end effect, which indicated that the uniaxial compression test should mitigate the coefficient of friction and increase the aspect ratio of specimens to make the observed strength of specimen more meaningful.