Precursory And Acoustics-thermal Effect Of Water Bearing Coal And Rock Failure Under Uniaxial Loading

Failure of coal and rock is the root cause of geological disasters such as water inrush,slope sliding and tunnel collapse.Accurate and effective monitoring and early warning of the failure process of coal and rock failure can provide reliable precursor information for rock and rock failure in the practice of mine,tunnel and other engineering.This paper mainly carries out infrared radiation and acoustic emission experiments for four kinds of coal and rock with different water content under uniaxial loading.The change rule of infrared radiation index(average infrared radiation temperature and variance of successive minus infrared image temperature,VSMIT)and acoustic emission index(correlation dimension of ringing counts based on fractal theory)of water bearing coal and rock in loading process is compared and analyzed.On this basis,the precursory and the acoustics-thermal effect of water bearing coal and rock failure is analyzed,and the acoustics-thermal precursory mechanism of water bearing coal and rock failure is discussed in this paper.The results are showed that:(1)VSMIT has mutation in the loading process of coal and rock with different moisture content,which is universal.The growth of rock specimens(2.5% water content)is the largest,with a ratio of 468.46%.The growth of rock specimens(0.5% water content)is the smallest,with a ratio of 81.55%.The growth of coal samples(1% water content)is the largest,with a ratio of 57.12%.The growth of dry coal samples is the smallest,with a ratio of 42.61%.According to the Pauta criterion,the three times standard deviation of VSMIT as the control line on the data screening.The mutation point which is over control line is used as the precursor of coal and rock failure.(2)The correlation dimension has a sudden drop in the loading process of coal and rock with different water content,which is universal.The reduction of correlation dimension of natural rock specimens is the largest,with a ratio of 58.26%.The reduction of correlation dimension of saturated rock specimens is the smallest,with a ratio of 45.63%.The reduction of correlation dimension of dry coal samples is the largest,with a ratio of 44.19%.The reduction of correlation dimension of saturated coal samples(1.5% water content)is the smallest,with a ratio of 37.63%.These drop points can be regarded as the acoustic emission precursor based on fractal theory of coal and rock failure.(3)There is spatial-temporal acoustics-thermal effect during the loading process of water bearing coal and rock.The temporal acoustics-thermal effect is shown in that the proportion of sample blocks within 5 seconds of time difference of VSMIT and correlation dimension corresponding to PUF is 72.50%.The spatial acoustics-thermal effect is shown in that there is a good correspondence between the position of the abnormal temperature region in the original infrared image sequences and the location of the crack in the three-dimensional positioning map of the acoustic emission.(4)This paper attempts to discuss acoustics-thermal precursory mechanism.When the micro cracks are aggregated and connected to a large crack,the proportion of large-scale cracks increases and clusters occur,and even a rupture surface occurs.The distribution of micro cracks in the coal and rock is developed from disorder to order.At the same time,due to the thermoelastic effect and the frictional thermal effect of mineral particles(or grains),the infrared radiation temperature field appears different phenomenon,leading to the increase of the infrared radiation temperature field dispersion.