This paper investigates the mechanisms of rock failure related to axial splitting and shear failure due to hoop stresses in cylindrical specimens. The hoop stresses are caused by normal viscous stress. The rheological dynamics theory (RDT) is used, with the mechanical parameters being determined by P- and S-wave velocities. The angle of internal friction is determined by the ratio of Young's modulus and the dynamic modulus, while dynamic viscosity defines cohesion and normal viscous stress. The effect of frequency on cohesion is considered. The initial stress state is defined by the minimum cohesion at the elastic limit when axial splitting can occur. However, as radial cracks grow, the stress state becomes oblique and moves towards the shear plane. The maximum and nonlinear cohesions are defined by the rock parameters under compressive strength when the radial crack depth reaches a critical value. The efficacy and precision of RDT are validated through the presentation of ultrasonic measurements on sandstone and rock specimens sourced from the literature. The results presented in dimensionless diagrams can be utilized in microcrack zones in the absence of lateral pressure in rock masses that have undergone disintegration due to excavation. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

A comprehensive understanding of shale's bedding anisotropy is crucial for shale-related engineering activities, such as hydraulic fracturing, drilling and underground excavation. In this study, seven Brazilian tests were conducted on shale samples at different bedding orientations with respect to the loading direction (0 degrees, 45 degrees and 90 degrees) and the disc end face (0 degrees, 45 degrees and 90 degrees). An acoustic emission (AE) system was employed to capture the evolution of damage and the temporal-spatial distribution of microcracks under splitting-tensile stress. The results show that the Brazilian tensile strength decreases with increasing bedding inclination with respect to the disc end face, while it increases with the angle between bedding and loading directions. Increasing the bedding inclination with respect to the end face facilitates the reduction in b value and enhances the shale's resistance to microcrack growth during the loading process. Misalignment between the bedding orientation and the end face suppresses the growth of mixed tensile-shear microcracks, while reducing the bedding angle relative to the loading direction is beneficial for creating mixed tensile-shear and tensile cracks. The observed microscopic failure characteristics are attributed to the competing effects of bedding activation and breakage of shale matrix at different bedding inclinations. The temporal-spatial distribution of microcracks, characterized by AE statistics including the correlation dimension and spatial correlation length, illustrates that the fractal evolution of microcracks is independent of bedding anisotropy, whereas the spatial distribution shows a stronger correlation. The evolution features of correlation dimension and spatial correlation length could be potentially used as precursors for shale splitting failure. These findings may be useful for predicting rock mass instability and analyzing the causes of catastrophic rupture. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/

The observation of precursory signals of the 2021 Chamoli rock-ice avalanche provides an opportunity to investigate the multidisciplinary analysis approach of rock failure. On 7 February 2021, a huge rock-ice mass detached from the Raunthi peak at Chamoli district in Uttarakhand, India. The tragic catastrophe resulted in more than 200 deaths and significant economic losses. Here, we analyse radon concentration and seismic signals to characterise the potential precursory anomalies prior to the detachment. Continuous peaks of radon anomalies were observed from the afternoon of 5 to 7 February and decreased suddenly after the event, while a cumulative number of seismic tremors and amplitude variations are more intensified similar to 2.30 h before the main event, indicating a static to dynamic phase change within the weak zone. This study not only characterises abnormal signals but also models the rock failure mechanisms. The analysis unveils three time-dependent nucleation phases, physical mechanisms of signal generation and a complete scenario of physical factors that affected the degree of criticality of slope failure. The results of this study suggest gradual progression of rock cracks/joints, subsequent material creep and slip advancement acceleration preceded the final failure. Furthermore, the study highlights the importance of an early warning system to mitigate the impact of events like the 2021 Chamoli rock-ice avalanche.