Tensile mechanical behavior of composite rocks under stress waves: A focus on strength variation between rock layers

Abstract

Composite rock layers are widely present in mining and tunnel construction projects, and are prone to dynamic tensile failure along bedding planes under dynamic disturbances. To ensure engineering safety, it is necessary to conduct research on the dynamic tensile characteristics under different working conditions. Considering the difficulty of on-site sampling, composite rock samples were prepared with cement mortar, and dynamic Brazilian splitting tests were carried out using split Hopkinson pressure bar (SHPB) equipment, a high-speed camera, and PFC^2D numerical software to explore their dynamic tensile properties under dynamic disturbance under different strength ratios and other factors. The results show that the dynamic tensile strength of samples exhibits a rising trend with the strength ratio and strain rate growth. As the incident angle increases from 0° to 90°, the stress contour deflects transform from center-splitting failure to tension-shear combined failure and back again. The influence of the incident order in different lithology rocks on the dynamic tensile strength of composite samples is controlled by strain rate, and when the strain rate increases to 400 s⁻¹, the difference in strength due to the sequence of incident stress waves is within 5%. Based on PFC^2D, the strength ratio of composite samples has a certain influence on the distribution of microfractures. With strength ratios equaling 1.5 or 2.0, the cracks are mainly concentrated on the softer material side, while a large number of cracks are distributed on both sides of the bedding plane with a strength ratio equal to 1.2.

Keywords

rock dynamics / strength ratio / composite rock / split Hopkinson pressure bar / dynamic tension / failure mechanism

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