Evaluation of characteristics and energy efficiency of granite cracking induced by high power laser horizontal irradiation
In view of the current engineering problems of slow drilling speed and large bit loss in the construction of hard rock tunnel by drilling and blasting method,the project idea of using high power laser horizontal irradiation of hard rock to quickly form holes instead of traditional PDC bit drilling was proposed.Feasibility test of granite perforation by high power laser horizontal irradiation was carried out to analyze the cracking characteristics of granite irradiated by high power laser horizontal irradiation.Uniaxial compression test,scanning electron microscope(SEM-EDS)and X-ray diffractometer(XRD)were used to analyze the mechanical properties and microscopic phase evolution of rock before and after laser action.The rock breaking velocity and specific energy of laser perforating and PDC bit drilling were compared comprehensively.The results show that"explosion-like crater"is formed on the rock surface after continuous laser irradiation,and the molten material accumulates at the bottom of the hole under the action of gravity,absorbes most of the laser energy at the bottom of the hole,and inhibites the thermal cracking reaction of the rock at the bottom of the hole.The longitudinal failure of rock is affected by gravity,and the distribution of molten material in the upper and lower pore walls is uneven.With the continuous irradiation of laser,the center of rock pore will continuously deviate from the incident point of light spot.The uniaxial compressive strength of rock samples decreases from 63.31 MPa to 42.36 MPa after being irradiated by 4.5 kW laser for 10 s,which is due to the increase of biomica mass fraction caused by the decomposition of albiar.The rock breaking speed and specific energy of 4.5 kW laser perforation increase by 95.03%and 15.3%compared with those of PDC bit drilling,which proves the effectiveness of high power laser horizontal irradiation of hard rock perforation.
tunnel engineeringlaser rock breakingpore-forming characteristicsthermal cracking characteristicspore-forming efficiency
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