| As one of the mainstream rock breaking technologies,mechanical rock breaking is widely used in tunnel excavation,ore mining,geological exploration and other fields.However,in the face of hard rock stratum with high strength,the wear degree of the bit will become larger,which will increase the cost of rock breaking and reduce the efficiency of rock breaking.The microwave-assisted rock breaking technology using microwave to irradiate the rock in advance can weaken the strength of the rock,so as to prolong the service life of the cutterhead,reduce the rock breaking cost,increase the rock breaking efficiency,and give full play to the advantages of mechanical rock breaking to the greatest extent.The existing studies pay more attention to the damage of rock caused by microwave irradiation,but there is no systematic and comprehensive research on the changes of rock mechanical properties after microwave irradiation.This study takes granite as the research object,sets microwave irradiation at different times,takes the temperature rise law,wave velocity change,dynamic and static tensile and compressive strength,hardness and absorption energy of rock after microwave irradiation as the research indexes,uses quasi-static automatic servo instrument and SHPB device to carry out static and dynamic mechanical tests,and simulates the impact and penetration of bit and rock in the actual excavation process to carry out dynamic and static penetration tests,Finally,the micro to macro crack damage analysis is carried out,and the influence law of microwave on the mechanical properties of granite is obtained.This subject mainly carries out the following tests on the samples after microwave irradiation:(1)The maximum surface temperature and wave velocity are measured by temperature camera and ultrasonic velocimeter to explore the law of temperature rise and wave velocity attenuation of rock.(2)Through the quasi-static automatic servo instrument and SHPB device,the dynamic and static mechanical test is carried out,and the dynamic and static penetration test is carried out to simulate the point load action between bit and rock in the actual excavation project,so as to explore the influence of microwave on the mechanical properties of rock.(3)The micro and macro cracks of the sample after microwave irradiation were observed by three-dimensional scanner,CT scanner and electron microscope to explore the mechanism of the effect of microwave irradiation on the mechanical properties of the sample.The main conclusions are as follows:(1)Through the measurement and analysis of the temperature and wave velocity after microwave irradiation,it is found that under the microwave irradiation for a short time of 30 s,the temperature and wave velocity change greatly and do not change nonlinearly.The specific change trend: with the increase of microwave irradiation time,the growth of temperature and the decline of wave velocity are not completely linear,and the change is relatively slow in the initial and later stages of irradiation.(2)The mechanical test shows that the dynamic and static strength and penetration resistance of granite samples show a downward trend with the increase of irradiation time.However,due to the random damage in the rock or the difference between the straight crystals,it shows a downward trend of fluctuation.The strength and penetration resistance energy of the final sample have a large decline compared with that without irradiation.It can be seen that microwave irradiation can effectively reduce the strength and penetration of rock,It is feasible to use microwave-assisted mechanical rock breaking.(3)Through the analysis of the damage of the sample after microwave irradiation,it is found that even 30 s short-time microwave irradiation will cause great damage to the rock,and the internal micro cracks and external macro cracks of the sample will increase to a great extent.The experimental research shows that high-power and short-time microwave irradiation can rapidly reduce the strength of rock,which shows that microwave irradiation in advance is conducive to mechanical excavation,reduce the loss of bit and improve the excavation efficiency.Therefore,microwave-assisted mechanical rock breaking is an effective and feasible method.However,the size effect,the cause of microwave cracking and the influence of microwave power have not been deeply discussed in this test,and further research will be carried out in the future. |
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