Effect of High Temperature and Inclination Angle on Mechanical Properties and Fracture Behavior of Granite at Low Strain Rate

Abstract

Comprehensive understanding of the effects of temperature and inclination angle on mechanical properties and fracture modes of rock is essential for the design of rock engineering under complex loads, such as the construction of nuclear waste repository, geothermal energy development and stability assessment of deep pillar. In this paper, a novel inclined uniaxial compression (inclined UCS) test system was introduced to carry out two series of inclined uniaxial compression tests on granite specimens under various inclination angles (0-20 • ) and treated temperatures (25-800 • C) at 5 • inclination. Experimental results revealed that the peak compression stress and elastic modulus gradually decreased, while peak shear stress increased nonlinearly with the increasing inclination angle; the peak compression and shear stress as well as elastic modulus slightly increased from 25 to 200 • C, then gradually decreased onwards with the increasing temperature. The effect of temperature on peak axial strain was the same as that on peak shear displacement. Acoustic emission (AE) results suggested that the relationship between crack initiation stress, inclination angle and treated temperature followed a similar trend as that of the peak compression stress and elastic modulus. Particularly, the crack initiation (CI) stress threshold and shear stress corresponding to CI threshold under 800 • C were only 7.4% of that under 200 • C and revealed a severe heat damage phenomenon, which was consistent with the results of the scanning electron microscopy (SEM) with the appearance of a large number of thermal pores observed only under 800 • C. The failure modes tended to shear failure with the increasing inclination angle, indicating that the shear stress component can accelerate sliding instability of rocks. On the other hand, the failure patterns with different temperatures changed from combined splitting-shear failure (25-400 • C) to single shear failure (600 and 800 • C). The study results can provide an extremely important reference for underground thermal engineering construction under complex loading environment.Sustainability 2020, 12, 1255 2 of 25 design and thermal disaster prevention. Furthermore, in these underground thermal projects, due to the complexity of the stress environment, rocks are often affected by complex loading. Combined compression and shear loading are among the most common forms of rock encounter, such as irregular chamber [11][12][13]. Compared with the pure compressional state, additional shear stress can contribute to the rock failure [14,15]. Once these heat-treated rock masses are exposed to combined compression and shear loading, they may be more prone to instability. Hence, study of the effect of heat treatment on the mechanical and fracture behavior of rock material under combined compression and shear loading is absolutely critical for underground engineering design.The influence of heat treatment on rock properties is mainly reflected on its physical and mechanical properties, microstructure and ...

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“…The C-CAST system is mainly composed of the top adapter, the bottom adapter, the limiting groove and the connecting components. The top and bottom adapters have the same structure and are symmetrically arranged in the experiment, consisting of the base and the locating dial [40,41]. The experimental system can realize the inclined loading of coal and rock samples, with an inclination range of 0 • -30 • and an interval of 5 • .…”

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