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AbstractThe stress state of composite rock joints has a significant impact on the overall stability of the rock mass. Studying the composite mechanism disk specimens with different matrix strengths and inclination angles under Brazilian splitting state is of great significance for improving the safety of surrounding rock. This research conducted Brazilian tests on different types of jointed composite disk specimens at different inclination angles and explored the effects of inclination angle and material strength on the mechanical properties and deformation characteristics of specimens. Clarified the failure mechanism of joint specimen. The experimental results indicate that the disk specimens under different inclination angles exhibit three typical failure modes. As the inclination angle increases, failure mode changes from Disk matrix failure (DM failure) to Disk matrix and structural failure (DMS failure), and ultimately to Disk structural failure (DS failure). Failure load, input energy, and strain energy of the specimen continue to decrease as the inclination angle increases and the matrix strength decreases. The decrease in matrix material significantly weakens the strength of the specimen, but this effect continues to decrease with the increase of inclination angle. DIC results show that as the inclination angle increases, the position of cracks exists from the loading end to the joint surface. Through theoretical analysis, it is found that as the inclination angle increases, the stress state at the center of the specimens changes from compression-shear state to shear state, and finally to tension state, corresponding to three failure modes: DM failure, DMS failure, and DS failure, respectively. [ABSTRACT FROM AUTHOR]

The freezing method is widely used in the construction of vertical shafts in water-rich strata. The formed frozen rock wall is often involved in the creep process, and in particular, the creep behavior of frozen fissured rock mass poses a great threat to construction safety. To better understand the creep instability law of ice-filled, fractured red sandstone under freezing and triaxial stress conditions, a series of triaxial creep tests on frozen red sandstone specimens containing a single, pre-existing flaw at −10°C and under a confining pressure of 4 MPa were carried out with a self-developed DRTS-500 subzero rock triaxial testing system. The multistage loading creep curves were obtained, and the evolution laws of deformation and damage for the frozen specimens in the primary (instantaneous), secondary (steady-state) and tertiary (accelerating) phases were analyzed. The nonlinear visco-elastoplastic constitutive model of red sandstone with a single ice-filled flaw was established according to the fractional calculus theory and the Kachanov damage theory. The results show that the initial creep property, unstable creep property and creep failure mode of frozen single-flaw red sandstone are significantly affected by the flaw dip angle. The proposed creep damage model can accurately describe the complete creep curves of frozen red sandstone with a single ice-filled flaw, especially in the unstable creep stage. The influences of the stress level and flaw dip angle on the creep parameters were analyzed, and sensitivity analyses of the characteristic creep parameters were carried out to verify the reliability and rationality of our creep model. This research can be applied to the assessment of collapse, cracking and other long-term failures and hence can be used as a theoretical basis of design in the freezing engineering of coal mine shafts. [ABSTRACT FROM AUTHOR]