Kinetic characterisation of sandstone exposed to high temperature-water cooling cycle treatments under the impact loading: from the perspective of geohazard

Enhanced Geothermal Systems (EGS) improve geothermal energy extraction but can rapidly cool high-temperature rocks, leading to internal fractures that weaken mechanical properties and pose risks such as well collapses and seismic events. Understanding the physico-mechanical changes in dry hot rocks, particularly sandstone, when high-temperature water cooling cycles is essential. This study examines the dynamic behavior of sandstone through impact tests at varying temperatures and cycles. Results show that as temperature and cycle count increased, peak dynamic stress decreased while dynamic strain increased. A critical temperature range of 500–600 ​°C was identified, beyond which significant changes in dynamic stress and strain occurred, indicating severe damage to the specimens’ stability. High-temperature water cooling cycles enhanced energy reflectivity and dissipated energy, reducing transmittance. The study revealed that between 200 and 400 ​°C, tensile damage predominated, while between 500 and 600 ​°C, compression-shear damage was dominant. Increasing temperature and cycles led to more extensive cracking and increased rock fragmentation. These findings provide a basis for assessing the stability of sandstone and offer theoretical insights into mechanical properties, energy transfer, and crack propagation in geothermal energy extraction, aiding in the prevention of geological disasters.