Mechanism of increasing or inhibiting laser-weakened rocks by saturated fluids and mechanical behavior of rocks after laser damage

• The mechanism of action of water on the efficiency of laser rock breaking was studied. • The spatial distribution characteristics of cracks in the rock were quantitatively analyzed. • The mechanical properties of rocks with different water content states after laser irradiation were studied. Laser technology has a wide range of application prospects as a novel means of assisting rock breaking. The realization of efficient laser-assisted breaking of deep hard rocks is based on revealing the mechanism of the saturated fluid increase or inhibition of laser-weakened rock. The laser irradiation of basalt with different water contents was used to analyze the mechanical response characteristics and investigate the destruction law of basalt under different laser power irradiations to explore the mechanism of the influence of water on the effect of laser rock breaking. The results show that the presence of water can significantly increase the drilling depth, and a laser irradiation of 1250 W can penetrate 56.5 mm deep into the rock in 30 s. The uniaxial compressive strength of basalt was reduced by a maximum of 38.23 % and the modulus of elasticity by a maximum of 74.99 % after the laser irradiation. Under low- power conditions, water has a positive effect on the laser rock-breaking efficiency. After 30 s of a laser irradiation in the range of 250–750 W, the uniaxial compressive strength of the water-saturated rock (WSR) samples was 12.64–13.43 % less than that of the original rock (OR) samples, and that of the natural state rock (NSR) samples was 1.09–3.93 % less than that of the OR samples. Both acoustic emission events and basalt energy significantly increased after a laser irradiation, and water promoted the expansion of rock microcracks. The degree of rock fragmentation increased with an increasing laser power. Laser irradiation can significantly reduce the strength of the rock, and water can effectively promote a low-power laser to break the rock, which is effective in reducing the difficulty and improving the efficiency of rock breaking. The obtained results provide theoretical and technical support for the application of the laser technology in the effective crushing of deep hard rock, and efficient and safe exploitation of deep resources.