Effect of thermal cycles on mechanical properties of a moderately weathered granite

• Published in: IOP conference series. Earth and environmental science 2021-10, Vol.861 (7), p.72146
• Main Authors: Bao, X H, Zhang, H J, Zhu, Q, Feng, S, Jia, J Q, Mei, G X
• Format: Article
• Language: English
• Subjects: Bedrock; Boring machines; Boring mills; Compressive strength; Drilling; Granite; Heat treating; Heat treatment; High temperature; Mechanical properties; Milling (machining); Modulus of elasticity; Rocks; Slurries; Temperature; Tunnel construction
• ISSN: 1755-1307; 1755-1315
• DOI: 10.1088/1755-1315/861/7/072146

The friction between the hard rock and milling wheels of a tunnel boring machine generates high temperatures. The high-temperature bedrock was then cooled down by circulating slurry. Therefore, thermal cycles were initiated within bedrocks. Understanding the response of mechanical properties of hard rock to these thermal cycles can be helpful in improving the drilling efficiency. In this study, uniaxial compressive strength and elastic modulus of a moderately weathered granite after various thermal cycles were determined. Results show that, for the specimens treated at a temperature of lower than 300°C, uniaxial compressive strength and elastic modulus decreased with the increasing numbers of thermal cycles. For the specimens treated at a temperature of higher than 400°C, uniaxial compressive strength and elastic modulus increased in the first six thermal cycles, and the tendencies reversed as the thermal treatment was further proceeded. For a given numbers of thermal treatment, uniaxial compressive strength and elastic modulus peaked at 200°C and began to decrease as the temperature further increases. These findings can be used to optimize the rotating speed of milling wheels during excavating granite bedrock.