Mechanical behavior and failure response characteristics of hard sandstones considering bedding dip angles

This study focuses on the mechanical behavior and failure responses of hard sandstones considering bedding dip angles. Through uniaxial compression tests of hard sandstones with different bedding dip angles, this study delved into the influence of bedding dip angles on the mechanical behavior of hard sandstones and the relationship between the bedding dip angles and fractal characteristics of hard sandstone fragments. The test results show that bedding dip angles produced negligible effects on the type of the stress-strain curves of hard sandstones. However, low dip angles (0°, 22.5°, and 45°) corresponded to unimodal curves, while high dip angles (67.5° and 90°) were associated with multimodal curves, with curve fluctuations primarily approaching peaks. At a dip angle of 67.5° (the most unfavorable bedding plane), peak stress σ_d and peak strain ε_d reached their minimum values of 46.25 MPa and 9.80×10⁻³, respectively. Bedding dip angles displayed more significant effects on the stress than on the strain of hard sandstones. Under the influence of bedding dip angles, hard sandstones manifested low anisotropy, with anisotropy degrees ranging from 1.32‒1.64. With an increase in the bedding dip angle, hard sandstones experienced the damage failure evolution from shear failure to shear-tension compound failure, then the shear failure of bedding planes, and finally splitting failure. Under uniaxial compression, hard sandstone fragments displayed distinct mass and fractal characteristics, dominated by moderate-size fragments. Furthermore, bedding dip angles had negligible effects on the mass distribution of fine-grained fragments, which exhibited fractal dimensions from 1−2. Additionally, a large proportion of fragments measured large sizes. The results of this study can serve as a theoretical reference for research on the stability of rocks with bedding planes and the disaster prevention and control of underground space engineering.