Work

Failure mechanisms and paths of freeze–thaw-treated single-flaw sandstone under triaxial compression in ultra-high-altitude cold-region open-pit mine slopes

Year: 2026

Type: article

Abstract: Ultra-high-altitude cold-region open-pit mine slopes are affected by seasonal freeze-thaw (F-T) weathering, structural discontinuities, and excavation-induced stress changes. Sandstone sampled from a mining bench at 5074 m a.s.l. in the Dahongliutan area of Hotan County, Xinjiang, China, was used to examine failure-path evolution under prior F-T history. To distinguish F-T pretreatment from subsequent mechanical loading, single-flaw specimens were first subjected to 0, 20, 40, or 60 air-freezing/water-thawing cycles and were subsequently tested under conventional triaxial compression with acoustic emission (AE) monitoring at confining pressures of 5, 10, and 15 MPa; flaw inclinations were 45° and 80°. The study addresses two questions: whether a pre-existing flaw remains the final macroscopic failure band after closure, and how flaw inclination biases path selection through normal-shear stress partitioning on the closed flaw plane. The final macroscopic failure band did not necessarily coincide with the pre-existing flaw. The 45° conditions more commonly exhibited flaw-tip interaction, path deflection, and oblique coalescence, whereas the 80° conditions were dominated by near-axial matrix paths and local branching. Under the idealized mean-stress transformation, τ/q = 0.50 for the 45° flaw and approximately 0.17 for the 80° flaw; the corresponding peak-load η = τ/σₙ values for the FT20 conditions were approximately 0.83–0.87 and 0.15–0.17, respectively. AE results showed that increased hit activity could precede the concentration of signals with higher AE waveform energy near the peak, while similar near-peak AE concentration could accompany different final paths. The combined evidence supports a load-transfer/path-competition interpretation in which the flaw is interpreted as evolving from an initial discontinuity into a closed internal contact interface; flaw inclination biases the competing paths, whereas AE primarily constrains the timing of localization. The stress transformation is used as a first-order mean-field interpretation and does not resolve local three-dimensional flaw-tip or partial-contact stresses.

Source: Scientific Reports

DOI: 10.1038/s41598-026-73655-9