Experimental Study On The Degradation Law Of Basalt Under Different Microwave Transmission Depths

Microwave irradiation can cause rock damage,resulting in thermal cracking of the rock,which is beneficial to tunneling and excavation.Therefore,studying the damage characteristics of rock under microwave irradiation is of great significance to promote the development of microwave-assisted rock breaking technology and has important theoretical significance and application value.However,the damage of the microwave to the rock is not constant,but will decrease as the depth of microwave transmission increases within a limited depth.Based on this,in order to study the relationship between rock damage and microwave wave penetration distance,the paper takes basalt as the research object and the external surface temperature,ultrasonic wave velocity and effective porosity are seen as the damage reference indexes,and the tensile strength is considered to the mechanical strength index.Through the combination of theory and experiment,the damage law of rock under different wave transmission distances is studied.The main research results are as follows:(1)By conducting microwave irradiation experiments with microwave transmission depths of 0 mm,25 mm,50 mm,75 mm,and 100 mm on basalt under different microwave irradiation power and time,It can be concluded that when the microwave wavelength is constant the ability of microwaves to penetrate rocks is limited.Within a certain range of microwave irradiation parameters,this ability has nothing to do with microwave irradiation power and irradiation time.When the microwave wavelength is limited to 12.3 cm,the microwave penetration distance of this type of basalt is between 50 and 60 mm,which is basically consistent with the theoretically calculated maximum wave penetration distance of this type of basalt of 51 mm.(2)By conducting microwave irradiation experiments on basalt with irradiating powers of 2 kW,2.6 kW,3.2 kW,and 4 kW,and irradiation time of 120 s,150 s,180 s,210 s respectively under different microwave transmission distances,it is concluded that within a certain range of microwave irradiation,the wave transmission distance is the key factor affecting the degree of rock damage.When the microwave irradiation power and time are the same,reference indicators such as the outer surface temperature of the basalt and the attenuation rate of the ultrasonic wave velocity will change significantly with the change of the wave transmission distance.It appears that the smaller the microwave transmission distance,the higher the temperature of the outer surface of the rock,and the greater the attenuation rate of the ultrasonic wave velocity.(3)The Brazilian split test on the basalt was performed after the microwave irradiation test and the attenuation rate of the tensile strength was analyzed.It is considered that when the rock is within the limit of the microwave penetration distance,the damage effect of the microwave on the rock follows the rule that the greater the irradiation power,the longer the irradiation time,the better the damage effect.at the same time,the test results also prove that when the wave penetration distance exceeds a certain limit,microwave irradiation will hardly cause damage to the rock.(4)From the energy point of view,the microwave irradiation energy provides the thermal stress required for the development of rock cracks.Therefore,the more microwave energy,the better the microwave destruction effect on the rock.The tensile strength of the rock increases with the increase of the wave transmission depth,which means that the accumulation and consumption of microwave energy in the rock is not uniform,but decreases with the increase of the wave transmission depth,and this also shows that the shorter the depth of wave transmission is more conducive to the destruction of rocks.