Thermal spallation is a non-contact rock-breaking method, in which the surface of the rock is rapidly heated to induce small flakes or spalls. Specific energy is usually used to evaluate the drilling performance, which is defined as the amount of energy required to remove a unit volume of rock. In this paper, a mathematical model for specific energy of thermal spallation is proposed. Thermal spallation experiments are carried out with granite, shale, and red sandstone. Main parameters in proposed specific energy model are measured to calculate the corresponding specific energy. Results show that under high temperature, the granite and shale can be induced to spall, while the red sandstone only fuses on the surface. For granite and shale, specific energy is small and close to their compressive strengths, which indicates that thermal spallation is suitable for heterogeneous hard rocks and is of high rock breaking efficiency. Moreover, for granite, the specific energy of thermal spallation is much smaller than that of other rock breaking methods in previous work, including mechanical bit, high pressure water jet, supercritical carbon dioxide jet and high power laser, which reveals that rock thermal spallation method is of high energy utilization and drilling efficiency.

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