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<p>High temperature and high stress are critical challenges facing enhanced geothermal systems (EGS). This study investigates the physical and mechanical behavior and acoustic emission (AE) characteristics of granite subjected to heating–water cooling treatments at temperatures ranging from 25 °C to 400 °C. Changes in physical properties, including volume expansion, mass loss, and P-wave velocity, were examined to quantify the extent of thermal damage. Results show that visible surface cracking occurs on granite samples treated above 300 °C, with P-wave velocity being the most sensitive indicator of thermal damage. Uniaxial and triaxial compression tests were conducted to explore the effects of temperature and confining pressure on granite’s strength, deformation, failure modes, energy evolution, and brittleness. While peak strength remains largely unaffected by temperature, failure modes transition from axial splitting to shear as confining pressure increases. Thermal damage reduces the rock’s energy storage capacity and increases energy dissipation during loading. The brittleness index decreases with temperature and confining pressure, though granite still exhibits pronounced brittle behavior within the studied range. Distinct differences were observed in the AE temporal characteristics and energy evolution of granite samples under uniaxial and triaxial compression conditions. As the specimen approaches failure, the abrupt increase in AE hit rate occurs earlier than the corresponding rise in AE energy. The global <i>b</i>-value of the granite samples increased with treatment temperature, and the global <i>b</i>-value in triaxial compression tests was higher than that in uniaxial compression tests. The evolution of timedependent <i>b</i>-value also varied with increasing confining pressure. These findings, particularly the AE temporal characteristics and distinct <i>b</i>-value evolution under confinement of thermally damaged granite, provide important implications for microseismic-based stability assessment and early warning in thermally damaged rock masses.</p>

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Mechanical Behavior and Acoustic Emission Characteristics of Thermally Damaged Granite under Confining Pressure

  • 期刊论文

  • 发表日期：

    2025年11月25日

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  • Pei Guo,
  • Yong Zhang,
  • Junjie Shi,
  • Jie Fang

摘要

High temperature and high stress are critical challenges facing enhanced geothermal systems (EGS). This study investigates the physical and mechanical behavior and acoustic emission (AE) characteristics of granite subjected to heating–water cooling treatments at temperatures ranging from 25 °C to 400 °C. Changes in physical properties, including volume expansion, mass loss, and P-wave velocity, were examined to quantify the extent of thermal damage. Results show that visible surface cracking occurs on granite samples treated above 300 °C, with P-wave velocity being the most sensitive indicator of thermal damage. Uniaxial and triaxial compression tests were conducted to explore the effects of temperature and confining pressure on granite’s strength, deformation, failure modes, energy evolution, and brittleness. While peak strength remains largely unaffected by temperature, failure modes transition from axial splitting to shear as confining pressure increases. Thermal damage reduces the rock’s energy storage capacity and increases energy dissipation during loading. The brittleness index decreases with temperature and confining pressure, though granite still exhibits pronounced brittle behavior within the studied range. Distinct differences were observed in the AE temporal characteristics and energy evolution of granite samples under uniaxial and triaxial compression conditions. As the specimen approaches failure, the abrupt increase in AE hit rate occurs earlier than the corresponding rise in AE energy. The global b-value of the granite samples increased with treatment temperature, and the global b-value in triaxial compression tests was higher than that in uniaxial compression tests. The evolution of timedependent b-value also varied with increasing confining pressure. These findings, particularly the AE temporal characteristics and distinct b-value evolution under confinement of thermally damaged granite, provide important implications for microseismic-based stability assessment and early warning in thermally damaged rock masses.