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.
Highlights
The temperature influence on mechanical behavior of rocks has attracted extensive attention in many geological engineering such as underground coal gasification [1], nuclear waste repositories [2,3] and geothermal energy exploitation [4], etc
A novel combined compression and shear test (C-CAST) system is used to study the mechanical response of granite specimens treated by various high temperatures under inclined compression conditions
The peak compression stress and elastic modulus gradually decrease with the increasing inclination angle, while the peak shear stress increases nonlinearly, indicating that the additional shear stress component may lessen friction resistance and accelerate crack initiation and propagation
Summary
The temperature influence on mechanical behavior of rocks has attracted extensive attention in many geological engineering such as underground coal gasification [1], nuclear waste repositories [2,3] and geothermal energy exploitation [4], etc. In these projects, rock mass frequently experiences temperature in the range of 700–900 ◦C [5,6]. 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. 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
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