Study on mechanical properties and failure mode of single-fissure sandstone discs under bi-directional linear loading

Abstract

The tensile failure of discontinuous geological rock masses in underground spaces is an enduring issue in geotechnical engineering. Understanding the mechanical behaviour and failure characteristics of cracked rock under tension is vital for the safe practice of underground projects. In this study, bi-directional linear load tests were conducted on single-fissure sandstone discs under different stress ratios i (axial stress P1: lateral stress P2) = 1:1, 2:1, 3:1, 4:1, and ∞:1, with crack inclination angles α = 0°, 30°, 45°, 60°, and 90°. The specimens’ deformation characteristics, acoustic emission features, and microfracture characteristics were recorded using the digital image correlation (DIC), PIC-2 acoustic emission(AE) system, and the scanning electron microscopic (SEM). The results showed that the strength at α = 0° was not significantly different from that of intact discs. The AE results and test results indicated that the peak load and initiation load decreased when increasing α and i, and the initiation load approached the peak load. In addition, when the stress ratio was small(i ∼ 1:1), the failure mode of the specimens was mainly controlled by the lateral stress P2. As i increased, the constraint of the lateral stress weakened, and the final failure mode of the specimens was primarily determined by the crack inclination angles. Furthermore, fracture trajectories between adjacent load points were shear cracks, fractures along the axial load line were tensile cracks, and the failure between the end of the fissure and the axial load point was a tensile-shear mixed crack with tensile failure as the dominant mode. DIC displacement vector analysis and SEM results confirmed these failure characteristics. The findings provide a reference for underground support structures' design and safety maintenance.