Dynamic behaviors of sandstone under true triaxial confinements: Triaxial Hopkinson bar tests

Deformation features of rocks exhibit dependences on both strain rate and confinement, understanding dynamic mechanical behaviors of rocks under confinement conditions is of significance in dealing with various rock engineering fields, such as underground excavation, penetration and blasting. In this study, a novel Triaxial Hopkinson pressure bar was used to study the dynamic properties of rocks having a multi-axial stress state. Dynamic compression tests for sandstone are conducted over a wide range of impact velocities under different true tri-axial confined conditions. Experimental results demonstrate that the initial confining stress not only affects failure patterns but also leads to an increase of rock strength. Also, under the same confinement condition, the dynamic compressive strength and the failure behavior of rocks change with the increase of impact velocity. The couple effects of confining stress and strain rate on rocks properties can be studied and revealed. In addition, Synchrotron X-ray micro computed tomography (micro-μCT) technique was adopt to non-destructively detect and reconstruct the facture network of rocks after impact under confinement conditions, and the relationship between fracture plane and confining stresses is finally clarified.