Research On The Development Of Micro-cracks In Rock Under Microwave Irradiation

Rock breaking is unavoidable job in tunnel excavation work. Traditional methods of rock fragmentation in reducing the consumption of machine, improving efficiency, improving construction environment and other aspects have certain restrictions. As a new technology,microwave-assisted mechanical rock-breaking has been developed rapidly to advance these conventional technologies. Existing researches show that microwave irradiation can weaken the rock strength effectively and improve the efficiency of mechanical crushing. Achieving the new microwave assisted mechanical rock system as the goal, it is necessary to explore the development of rock cracks under microwave irradiation.A method which combines experiment and numerical simulation is adopted, the development of rock cracks under microwave irradiation is studied. Considering the influence of microwave irradiation parameters, cooling ways, mineral particle size and shape, the strength weakening laws of rock under microwave irradiation are studied by means of laboratory tests; the development of rock cracks under microwave irradiation is studied by means of numerical simulation method. Specific research contents and conclusions are as follows:(1)This paper explains the damage mechanism of rock caused by microwave irradiation according to the aspects of theory, and the main factors influencing the rock damage are analyzed. The rates of microwave power dissipation and the thermal expansion coefficient among various mineral particles are different. In the process of microwave irradiation, the absorbing minerals in the rock form the "hot spot", temperature gradient is formed around the minerals, which generates thermal stress and induces the rock damage.(2)Microwave irradiation and the rock mechanics experiments of rocks are performed with different microwave irradiation parameters. The influence factors such as microwaveirradiation parameters, cooling ways, mineral particle size and shape are considered, and the influence laws show: there is the best microwave irradiation time, under a certain microwave power, it will cause the waste of energy if the time is more than the best irradiation time; the effective method to improve the efficiency of microwave energy is to raise the microwave power; the particle size has a great influence on the effect of microwave weakening rock, the greater the particle size is, the less consumption of microwave energy will be needed; the mineral with irregular will cause thermal stress singularity and produce thermal stress concentration easily, the absorption of microwave energy to produce the cracks is small.(3)The model of two phase rock is established by using discrete element software PFC2 D. The development evolution law of mesoscopic cracks inside the rock is obtained by simulation of microwave irradiation, the factors influencing rock weakening under microwave irradiation are analyzed. The results show: there is the best microwave irradiation time, in which the formation and development of cracks are rapid; with the same output of energy,improving the microwave power can increase the quantity of cracks effectively, and can improve the degree of rock weakening. The influence of the absorbing mineral content,particle size and shape to the development of rock cracks under microwave irradiation is verified.