Abstract
To evaluate the stability and compactness of high-temperature underground construction, it is necessary to test the fracture toughness of surrounding rock (red sandstone) under real-time high temperature. In this paper, SCB specimens recommended by the International Society for Rock Mechanics are used to measure the mode I fracture toughness of red sandstone at real-time high temperatures. Also, to reveal its fracture characteristics and fracture mechanism, the fracture morphology observation (SEM experiment), XRD experiment, mercury intrusion porosimetry testing, and fractal measurement of fracture trajectory are carried out on the red sandstone specimens at various temperatures. The results show that (1) temperature may have a significant impact on the fracture toughness and fracture characteristics of red sandstone. On the whole, the fracture toughness values decrease with the increase in temperature, while the fractal dimensions of fractal trajectories increase with the increase in temperature. (2) Temperature has a significant influence on the fracture mode of red sandstone. At relatively low temperatures (20°C–400°C), the main fracture mode is transgranular failure. At relatively high temperatures (400°C–700°C), the fracture mode is mainly intergranular failure. (3) The weakening mechanism of red sandstone is mainly due to the effect of thermal dehydration when the temperature is between 100°C and 400°C. When the temperature is between 400°C and 700°C, the weakening mechanism is mainly due to thermal cracking and theα-βphase transition of quartz.
Highlights
In the deep geological disposal of high-level radioactive waste such as nuclear waste, the design requirements of surrounding rock and artificial barrier system are very strict
[32, 33], the edge cracked circular specimen subjected to wedge loading [34], the center-cracked ring specimen subjected to diametral compression [35], the single-edge-cracked round bar in the bending test [36], noncircular shape specimens such as the edge-cracked rectangular beam specimen subjected to three- or four-point bending [37, 38], the short rod (SR) test [38, 39], the central straight through the Brazilian disk test [33], the cracked chevron-notched Brazilian disk (CCNBD) test [40, 41], the SCB test, and the straightnotched disk bending test [42], and edge crack triangular (ECT) specimen [43]. e International Society for Rock
The fracture toughness of sandstone at different temperatures has a certain degree of discreteness, which is mainly due to the structural differences of sandstone. e variational trend of fracture toughness of sandstone with temperature has the following characteristics: (1) with the increase in temperature, the value of fracture toughness of sandstone first increases decreases; the value of fracture toughness reaches the maximum at 100°C, which is 4.27 MPa m0.5, and the value is 0.18 MPa m0.5 when the temperature rises to 700°C, which is 95.7% lower than that at 100°C. is fully demonstrates that the fracture behaviors of sandstone are greatly affected by high temperature
Summary
In the deep geological disposal of high-level radioactive waste such as nuclear waste, the design requirements of surrounding rock and artificial barrier system are very strict. It is necessary to consider the original strength of surrounding rock as well as the influence of thermal stress on its microstructures. To prevent the leakage of nuclear wastes, it is essential to study the evolutional processes of mechanical strength and internal microstructures of surrounding rock at high temperature in real time. In the fields of geothermal resource development, oil and gas and coalbed methane development, oil and gas geological storage, deep underground space utilization, and marine deep well drilling [5,6,7,8], it is necessary to study the variational trend of physical and mechanical parameters of rock at high temperature and its weakening mechanism.
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