Undrained SHPB experiments on calcareous sand with different saturation degrees

Abstract

Abstract Extensive research has been conducted on the impact behavior of unsaturated sand at high strain rates. However, achieving the undrained boundary condition remains a persistent challenge, leading to an inconsistent understanding of the dynamic responses of sand with varying saturation degrees. In this study, a novel sleeve designed to conduct Split Hopkinson Pressure Bar (SHPB) tests under undrained boundary conditions. Furthermore, drained SHPB tests were carried out by using the conventional steel sleeve as references. The absolute particle crushing distributions within various size ranges were investigated by utilization of dyed calcareous sand. Results revealed that, for the conventional drained sleeve, the locking-up phenomenon of full saturation sand was only observed at strain rate of 750 s− 1. However, locking-up occurs at all strain rates for undrained sleeve. The locking-up stiffness at strain rate of 750 s− 1 was 1.2 and 2.9 times larger compared to that at strain rate of 500 s− 1 and 250 s− 1, respectively. The locking-up stiffness increase with increasing strain rates under the fully undrained boundary conditions. Moreover, for the drained sleeve, negligible reductions on Br up to 10.8% were observed in measured Br if saturation degrees change from 0–100%. In contrast, for the undrained sleeve, the maximum reduction on Br was 47.6% and increases rapidly with increasing strain rates. The particle crushing was more sensitive to saturation degree at higher loading strain rates under undrained boundary conditions.