To ensure the stability of the borehole surrounding rocks during geothermal energy extraction and improve the efficiency of the process

single radial compression mechanical tests were conducted on energy-storing granite with internal sleeves. Using multiple monitoring devices

including the VIC-3D non-contact full-field strain system

a static strain testing and analysis system

this study investigated the damage characteristics and internal energy evolution of the borehole surrounding rocks under complex geological conditions such as high temperature and thermal cycling. Additionally

a failure criterion was established. The results indicate that the load-displacement curve of the single radial compressed energy-storing granite with internal sleeves exhibits a distinct pre-peak concave segment and linear segment under various conditions. Post-peak behavior is influenced by the sleeve and rock heterogeneity

showing two patterns: a rapid steep drop

or a drop followed by recovery

or leveling off before dropping again. The final failure mode is fragmentation into three or four pieces. Damage initiates with cracks at the inner borehole wall

parallel to the loading direction

followed by cracks at the outer borehole wall

perpendicular to the loading direction. Adding sleeves reduces crack width; fracture morphology and crack growth are partly influenced by the bonding between the rock sample and the sleeve. Energy evolution analysis reveals that the total pre-peak energy grows exponentially. We analyzed the relationship between energy and sleeve thickness by examining the proportions of elastic and dissipated energy relative to total pre-peak energy. A sleeve thickness of 1.0−1.5 mm provides the optimal enhancement. Based on theoretical analysis

we developed a failure criterion for energy-storing granite with internal sleeves and validated its accuracy.