Thermal-Damage-Controlled Rotary Cutting of High-Temperature Rocks: Evolution Characteristics and Energy Mechanisms

Deep tunnelling, mineral extraction and geothermal development increasingly encounter high-temperature rock masses whose thermal damage changes strength, deformation, fracture behaviour and the response of mechanical rock-breaking systems. This study investigates the evolution characteristics and energy mechanisms of rotary cutting in thermally treated green sandstone, red sandstone, marble and granite. Specimens were treated at 25, 200, 400 and 600 °C and tested using a laboratory digital drilling system that synchronously recorded drilling thrust, torque, rotational speed and penetration depth. Rotary-cutting specific energy was evaluated as the total axial and rotational mechanical energy consumed per unit volume of rock removed. The results show a repeatable three-stage process consisting of rapid initial adjustment, transitional fluctuation and stable working. At room temperature, the stable thrust levels were approximately 348 N for marble, 352 N for red sandstone, 358 N for green sandstone and 405 N for granite; the associated ±10, ±12, ±15 and ±20 N values denote typical stable-stage temporal fluctuation half-ranges rather than standard deviations or standard errors. Increasing temperature generally reduced thrust and torque, accelerated penetration and decreased steady specific energy, with the most pronounced changes occurring above about 400 °C. From 25 to 600 °C, granite specific energy decreased from 19.99 to 9.43 J/mm³ and red sandstone from 5.13 to 2.54 J/mm³, while marble decreased from 2.07 to 1.56 J/mm³. The 400–600 °C interval is interpreted as a critical response range in which stronger thermal degradation is consistent with changes in failure behaviour and energy partitioning; for quartz-bearing rocks, the α–β quartz transition may contribute, but this mechanism is literature-supported rather than directly observed here. Overall, thermal damage reduces cutting resistance and specific energy while improving rock-breaking efficiency, although severe damage may increase parameter dispersion and reduce operational stability.