• Mineral-based indices were 0.779, 0.671, and 0.267. • UCS and energy indices confirmed highest sandstone brittleness. • Failure-response indices reached 0.88 in sandstone. • Radar-chart integration ranked sandstone > siltstone > limestone. • Scenario-based weighting improved engineering adaptability. Rock brittleness is a key factor governing excavation stability, failure mode and energy release in underground engineering, but its evaluation remains inconsistent because existing indices rely on different concepts and test procedures. This study develops a multi-parameter brittleness index system that integrates five representative indices based on mineral composition, the ratio of uniaxial compressive strength to tensile strength, elastic parameters from the pre-peak stress–strain response, energy partitioning during loading and unloading, and post-peak failure characteristics including stress drop and volumetric dilation. Nine specimens were tested, three each of limestone, sandstone and siltstone, with uniaxial compressive strength in the range 21.51–47.40 MPa and indirect tensile strength in the range 2.83–3.81 MPa. All indices were normalized to 0–1 and assigned equal weight, and a radar chart was used to visualize and compare the integrated brittleness profiles. The results show that sandstone exhibits the highest brittleness across all five indices and encloses the largest radar area, limestone combines a relatively high strength-based index with the lowest mineral-based index due to its carbonate-dominated composition, and siltstone presents an intermediate overall level with marked brittleness in the energy-based and failure-response indices despite its lower strength. The radar-chart evaluation therefore indicates an overall brittleness ranking of sandstone, siltstone and limestone in descending order. The proposed framework enables a more direct comparison of brittleness among limestone, sandstone, and siltstone, and supports scenario-oriented interpretation for excavation and rockburst assessment.
Tao et al. (Fri,) studied this question.