高功率激光水平辐照花岗岩致裂成孔特性及成孔能效评价

Evaluation of characteristics and energy efficiency of granitecracking induced by high power laser horizontal irradiation

针对当前硬岩隧道钻爆法施工钻孔速度慢、钻头损耗大的工程难题,使用高功率激光水平辐照硬岩快速成孔替代传统PDC钻头钻孔,开展高功率激光水平辐照花岗岩成孔的可行性试验,分析高功率激光水平辐照花岗岩的致裂成孔特性;通过单轴压缩试验、扫描电子显微镜(SEM-EDS)和X射线衍射仪(XRD)衍射试验分析激光作用前后岩石的力学性能和微观物相演变;综合对比激光射孔与PDC钻头钻孔的破岩速度和比能。研究结果表明:岩石表面在激光持续辐照后形成“类爆炸坑”,产生的熔融物在重力作用下堆积在孔底,吸收了孔底处大部分的激光能量,抑制了孔底岩石的热裂反应;岩石的纵向破坏受重力影响导致上下孔壁熔融物分布不均匀,随着激光持续辐照,岩孔中心将不断向下偏离光斑入射点;经功率为4.5 kW的激光水平辐照10 s后,岩样的单轴抗压强度从63.31 MPa降低至42.36 MPa,其原因是钠长石分解引起岩样中黑云母的质量分数增加;功率为4.5 kW激光射孔的破岩速度较PDC钻头钻孔的破岩速度提高95.03%,比能增加15.3%,证明了高功率激光水平辐照硬岩成孔的有效性。

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"explosionlike 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.