Abstract
The thermal cracking of rocks is the phenomenon of expansion and deformation of mineral particles inside the rocks. The thermal deformation of the same granite sample under different heating pathways was meticulously analyzed, and the effect of the variation of external stress on the thermal expansion was carefully studied. The thermal deformation threshold temperature was low under triaxial stress, and a larger expansion was produced under uniaxial stress. The thermal deformation of the rock mass was found to be irreversible. Upon heating to the same temperature, the expansion was found to decrease with the increase in the number of thermal cycles. Besides, for each thermal cycle, the amount of deformation caused by cooling was always greater than the amount of deformation caused by temperature rise; this difference in deformation was especially obvious under a change from triaxial stress to uniaxial stress. In the process of elevated temperature which has the same heating rate, the thermal expansion coefficient was greater under uniaxial stress than it was under triaxial stress; under same external stress, the thermal expansion coefficient with a high heating rate was generally greater than the thermal expansion coefficient with a low heating rate.
Highlights
It has become very important to realize the significance of the study of the thermal deformation of granite under high temperature and pressure. e highly radioactive elements under the deep burial of nuclear wastes are expected to increase the temperature of the surrounding rock masses up to 300°C within the ten years. e penetration of the radiation from the radioactive elements through the surrounding rocks into the biosphere will have a serious consequence on the environment that humans live [1,2,3,4,5,6]
Results and Analysis of Axial Strain. e thermal deformation of rock is mainly caused by the thermal expansion of mineral particles inside the rock. e deformation characteristics are related to the intrinsic properties of rock such as the mineral composition, particle size, degree of pore and crack development, and the integrity of its internal structure
When the temperature is lowered, the thermal stress gradually disappears. e mineral particles after the thermal expansion at high temperature decrease in volume when cooled. e other mineral particles occupy the reduced volume during the process of adjusting the position, and the degree of opening of the crack is reduced and is sometimes compressed enough to even close. e internal structure of the rock changes when subjected to high temperature, and the solid skeleton constructed by the harder mineral particles gets damaged, reducing the bearing capacity of the rock signi cantly
Summary
It has become very important to realize the significance of the study of the thermal deformation of granite under high temperature and pressure. e highly radioactive elements under the deep burial of nuclear wastes are expected to increase the temperature of the surrounding rock masses up to 300°C within the ten years. e penetration of the radiation from the radioactive elements through the surrounding rocks into the biosphere will have a serious consequence on the environment that humans live [1,2,3,4,5,6]. It has become very important to realize the significance of the study of the thermal deformation of granite under high temperature and pressure. In the 1980s, Ramana had demonstrated that the thermal expansion coefficient of granite increases with increasing temperature when granite was heated in free state [15]. Homand-Etienne and Houpert had heated different kinds of granite from room temperature to 600°C and visualized the crack densities and size on the surface of granite rocks by scanning electron microscopy (SEM). Van der Molen studied the association between the transition temperature of α-β quartz, and the thermal expansion of granite at high pressure and found that the confining pressure impeded the cracks from opening [17].
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