Measurements of the longitudinal modulus of Pierre clay shale at varying strain rates

The propagation speed of finite-amplitude compressional waves of strain-rate 10 ³ - 10 ⁴ sec (super -1) in Pierre clay shale have been measured using shock wave techniques. The inferred longitudinal modulus perpendicular to the bedding is approximately a factor of four higher than that measured by others in uniaxial strain tests at strain rates of 1-5 sec (super -1) . The present shock wave speeds measured in the laboratory and in-situ finite-amplitude explosive experiments measured by others correlate more closely with field seismic velocities than with laboratory uniaxial strain measurements. Elastic properties of this highly saturated friable material measured parallel to the bedding are less sensitive to sampling disturbances than those measured in the perpendicular direction.