Dynamic Brazilian Tests of Granite Under Coupled Static and Dynamic Loads

Abstract

Rocks in underground projects at great depth, which are under high static stresses, may be subjected to dynamic disturbance at the same time. In our previous work (Li et al. Int J Rock Mech Min Sci 45(5):739-748, 2008), the dynamic compressive behaviour of pre-stressed rocks was investigated using coupled-load equipment. The current work is devoted to the investigation of the dynamic tensile behaviour of granite rocks under coupled loads using the Brazilian disc (BD) method with the aid of a high-speed camera. Through wave analyses, stress measurements and crack photography, the fundamental problems of BD tests, such as stress equilibrium and crack initiation, were investigated by the consideration of different loading stresses with abruptly or slowly rising stress waves. The specially shaped striker method was used for the coupled-load test; this generates a slowly rising stress wave, which allows gradual stress accumulation in the specimen, whilst maintaining the load at both ends of the specimen in an equilibrium state. The test results showed that the tensile strength of the granite under coupled loads decreases with increases in the static pre-stresses, which might lead to modifications of the blasting design or support design in deep underground projects. Furthermore, the failure patterns of specimens under coupled loads have been investigated. Travelling time of the stress wave (s) r t Dynamic tensile strength of the specimen (MPa) r c Dynamic compressive strength of the specimen (MPa) r 0 Amplitude of the assumed stress pulse (MPa) P Static force applied on the specimen (N) P c Equivalent force applied on the specimen under coupled loads (N)

An Experimental Study of Dynamic Tensile Failure of Rocks Subjected to Hydrostatic Confinement

“…1. From a macroscopic point of view, the bending of the roof induces tensile stress at the roof of the opening; from a microscopic view, the discontinuities in the rock result in tensile stress locally around the opening, so the dynamic tensile failure of rocks under pre-tension has been investigated by researchers (Wu et al 2015;Zhou et al 2014). However, the far-field rocks under hydrostatic pressure can also fail in tension under dynamic loads.…”

Brazilian Tests on Transversely Isotropic Rocks: Laboratory Testing and Numerical Simulations

“…The main failure mechanism in this case is tensile splitting of the rock matrix, and the corresponding tensile strength can be deduced. Zhou et al (2014) recorded the crack growth process by using a high-speed camera in dynamic Brazilian tests of granite. The initial crack propagated from the disc center to the boundary, which shows similar crack growth process compare to numerical results of h = 0°and 90°.…”

Experimental and Numerical Evaluation of Rock Dynamic Test with Split-Hopkinson Pressure Bar

“…The result shows that, by virtue of the ramped wave loading, the force equilibrium of the specimen can be effectively achieved and the rupture is precisely measured to synchronize with the peak force, both of which guarantee the quasi-static data reduction method employed to determine the dynamic flexural strength by Xu et al [21]. A series of rock cutting tests were performed to investigate the influence of back rake angle on the critical failure mode transition depth by Zhou et al [22]. It is found that the critical failure mode transition depth increases with the back rake angle.…”