Thermal-response zonation and spatiotemporal evolution of surface temperature in sandstone under laser irradiation

As shallow, easily accessible mineral resources are progressively depleted, the extension of mining operations into deep rock masses has become an inevitable trend. Traditional mechanical rock breaking techniques often encounter challenges under deep-seated, high confining pressure, and hard rock conditions, such as reduced drilling efficiency, accelerated drill bit wear, and environmental impacts. Laser rock breaking technology, leveraging significant advantages such as high energy density, high interaction efficiency, and the capability for remote, contactless fragmentation, holds broad application prospects in deep rock engineering. Taking typical deep-buried hard sandstone from Western China as the research object, this study utilizes a self-developed laser-induced fracturing and weakening test apparatus combined with Finite Element Method (FEM) numerical analysis. It systematically investigates the zonal characteristics of the thermal response and the spatiotemporal evolution of the temperature field on the sandstone surface under laser irradiation. The results indicate that the temperature field on the sandstone's upper surface exhibits a typical Gaussian distribution. With increasing laser irradiation time, the overall surface temperature rises and shows a trend towards gradual homogenization. Laser power is a crucial factor influencing the rock's thermal response; an increase in laser power leads to a continuous rise in both the heating rate and the temperature gradient. An increase in spot diameter results in a more uniform distribution of the laser beam energy, leading to an expanded Heat-Affected Zone (HAZ), but weakens the energy concentration effect in the central region. Increased rock thermal conductivity enlarges the laser HAZ but causes an overall decrease in the temperature level. Conversely, an increase in specific heat capacity and a decrease in absorptivity reduce the laser HAZ and lower the overall temperature level. The research findings systematically reveal the zonal characteristics of the thermal response and the evolutionary laws of the temperature field in sandstone under laser irradiation. This provides a reliable basis for the quantitative understanding of the laser fragmentation mechanism in deep hard rock, and offers a reference for theoretical research on deep-rock laser rock breaking and for parameter selection in practical laser rock breaking engineering.