| With the development of mineral resources entering the deep mining stage,the ground stress of deep rock mass is more complex,and the strength of rock is significantly increased compared with the shallow part,so the difficulty and cost of deep roadway excavation and support are significantly increased,which undoubtedly limits the development of deep mineral resources.In recent years,there has been great development of new rock breaking technologies that use high-pressure water jet,liquid nitrogen cracking,microwave radiation,impact drilling and other methods to improve tunneling efficiency.However,under the engineering background of complex stress condition of deep rock mass,high rock strength and difficult support.Non-contact high energy laser assisted mechanical rock breaking technology has the advantages of low disturbance,high speed,high efficiency and high automation,and can better adapt to the working conditions and requirements of deep excavation.Throughout the years of research on laser rock breaking by domestic and foreign scholars,it can be seen that the mechanism of action of high energy laser on rock is still inconclusive,and the mechanism of action of laser on soft rock is rarely studied.Under the condition that laser has the effect of high temperature thermal cracking and perforation on both hard and soft rocks,the mechanism of laser on rock is revealed by taking advantage of the characteristic that soft rocks have the effect of magnifying laser radiation.In this thesis,the laser radiation experiment of coal measure rock samples is designed and carried out,and the Brazilian splitting experiment is used to test the tensile strength of the rock samples in control group and radiation group.At the same time,using high-definition cameras,metallographic microscopes,infrared thermal imagers,scanning electron microscopes,X-ray diffractometry and DIC,acoustic emission and other analytical techniques,The radiation phenomena,the temperature field of molten pool,the characteristics of laser radiation path,the structure of radiation cavity,the characteristics of splitting failure and deformation,and the changes of mineral composition before and after rock radiation were monitored and analyzed with high precision.The experimental data and analysis results show that,on the whole,the high power density laser radiation has the strength weakening effect on the three coal measure rock samples,but under the support of radiation products and their structures,the tensile strength of some rock samples increases instead of decreasing.The results show that the surface temperature of rock samples rises sharply to melting point under the radiation of high power density laser,which leads to high thermal stress in the radiation area and surrounding area,and then leads to thermal fracture.With continuous laser heating and high pressure gas washing action,the rock melts and is washed out,forming perforated structures and radiation cavities.In this process,higher power density and rock sample water content significantly promote the efficiency of laser perforation,and water vapor plays a role in the promotion of laser perforation.For different rock samples,there are significant differences in the perforation efficiency of the same radiation parameter configuration,indicating that the rock type also has a significant effect on the laser perforation,which is caused by different mineral components and hydrologic properties.There are 36 figures,7 tables and 87 references in this thesis. |
