[This article belongs to Volume - 54, Issue - 09]
Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-13-11-2022-405

Title : Mechanical Properties of Fine Grained Dense Granite Affected by Thermal Cycles
ZHANG Jianguo, FENG Gan, WANG Xiaochuan, KANG Yong,

Abstract :

Deep geotechnical engineering often faces complex variable temperature environments. The thermal cycle effect of rock mechanical properties is important for the stability evaluation of reservoir and surrounding rock and the rational utilization of rock materials. For fine grained dense granite geothermal reservoir, its mechanical properties are related to energy-efficient exploitation and engineering safety. Therefore, thermal cycling experiment, uniaxial compression experiment, and optical microscope observation experiment were carried out to study the failure characteristics, the changes in mechanical parameters, and the influence mechanism of fine grained dense structure on the mechanical properties of granite. The results showed that the changing trend of rock failure characteristics and mechanical properties with the temperature and times of thermal cycle was closely related to the structure. For the fine grained dense granite, the uniaxial compressive strength and elastic modulus gradually decreased with the increase of upper limit temperature and times of thermal cycle, and the reduction rate of compressive strength became slow after more than 10 thermal cycles. The increase of the upper limit temperature of the thermal cycle can improve the sensitivity of the mechanical properties of granite to the deterioration of the thermal cycle. Internal thermal cycling at 300 ℃ would not change the brittle failure characteristics of fine grained dense granite. The microscopic observation and analysis show that the thermal cycle could significantly promote the crack propagation of granite. After 20 thermal cycles at 20~300 ℃, the linear crack density was 1.69 mm–1, which was 1.5 times that of one thermal cycle. Due to the fine and dense structure, the expansion and compaction effect of granite mineral particles was constrained, resulting in the predominance of crack initiation and propagation evolution induced by thermal stress, and then the macro mechanical parameters decreased nonlinearly with the corresponding linear crack density. This study had a certain reference value for the exploration of deep geotechnical engineering mechanics problems in variable temperature environments