Damage characteristics of high-temperature coal under different cooling rates

• Water-cooled coal samples show faster crack growth than naturally cooled ones. • Water cooling enlarges pores, increasing permeability and reducing ultrasonic velocity. • The maximum thermal shock factor quantifies water cooling damage on coal specimens. • In the initial stage of water cooling, the maximum thermal shock factor occurs on the surface. The damage characteristics of high-temperature coal under water cooling was analyzed.As the heating temperature increases, the internal pore development and crack propagation in coal intensify, with the failure mode gradually shifting from brittle to plastic. There exists a threshold temperature that accelerates damage. The rapid temperature drop caused by water cooling accelerates damage and cracking in the coal. The thermal shock factor resulting from the rapid temperature drop can quantitatively represent the damage induced by water cooling. The results are expected to provide guidance for the utilization of thermal energy in coal field fire areas.