Strain rate effects in Kimmeridge bay shale

Abstract Many rocks are known to exhibit a small increase of compressive strength over orders of magnitude of increasing strain rate. This paper presents evidence for a much greater rate effect as seen in triaxial compression tests on a comparatively soft, saturated shale from Kimmeridge Bay, Dorset, U.K. The effect, which is attributed to an intrinsic property of the shale, produces an increase in both strength and strain to failure of the order of four and seven failed specimens in a scanning electron microscope have revealed an associated change in failure mode at a well-defined “critical” rate. The mechanisms responsible for the effect are discussed.