Mohr–Coulomb and Modified Hoek–Brown Strength Criteria of Layered Sandstone Considering the Unloading Effect and Anisotropy

The Mohr–Coulomb (M-C) and Hoek–Brown (H-B) strength criteria are widely used in various engineering fields, such as mining engineering, tunnel engineering and so on. To investigate the M-C and H-B strength criteria considering the unloading effect and anisotropy, series of triaxial loading (unloading) tests on layered sandstone were conducted. The results revealed that the peak strength was significantly affected by the unloading effect. Moreover, the cohesion and internal friction angle had a significant nonlinear relationship with the bedding angle. Additionally, the M-C and modified H-B strength criteria were established considering the unloading effect and anisotropy. Then, according to the strength criteria established, the peak strength could be estimated theoretically. Furthermore, compared to the M-C strength criteria, the modified H-B strength criteria were more appropriate for accurately estimating the triaxial compressive strength of layered sandstones. The conclusions obtained could provide certain references for the stability control of deep excavation engineering.