Dynamic tensile behaviour of rocks under confining pressure and high-rate loadings

Tensile cracking is a predominant mode of failure in rocks within underground resource excavation and engineering structures, where rocks are frequently subjected to dynamic disturbances while simultaneously experiencing in-situ stresses. This paper proposes a new dynamic split tension setup utilising a cubic specimen to investigate the dynamic behaviour of rocks across various tensile strain rates and confining pressures. The objective is to extend the applicability of the triaxial Hopkinson bar in studying dynamic behaviour of geomaterials. For comparison, the dynamic Brazilian disc (BD) tests were performed using three rock types (e.g., sandstone, granite and marble) under different strain rates ranging from 10−3∼102 s−1. Besides, the Digital Image Correlation (DIC) technique was adopted to measure full-field real-time tensile strain of rocks and demonstrated that tensile crack initiated at the middle part and split the specimen into two similar halves. Effects of specimen size, geometry, loading rate as well as the confining pressure are investigated in detail. The dynamic fracture behaviours, including dynamic tensile strength, tensile strain, time to fracture and dynamic increase factor (DIF), were characterised for the rocks. It is found that dynamic tensile strength of rock minimal dependence on size and geometry but is significantly influenced by loading rate and confinement. It exhibited a linear increase with strain rate (100∼102 s−1) and demonstrated a nonlinear growth with lateral confinement from 0 to 15 MPa. The nonlinear dependency on confinement can be attributed to the restriction imposed on the opening and propagation of tensile cracks due to the presence of confinement. These findings enhance our understanding of the safety aspects associated with underground rock excavations, particularly in situations where considering in-situ stress is crucial for evaluating the dynamic tensile failure of rocks.