Experimental Study On Joint Monitoring With Infrared And AE Technology In Rock Failure Process

Rock disastrous fracturing due to overloading will cause many changes of physical phenomena such as electromagnetic radiation (include infrared radiation), acoustic emission, deformation, temperature and so on. By combining different monitoring methods and analyzing various information can solve the problem that single source can not identify or accurately identify precursors of rock disastrous fracturing.First, this paper focused on the quantitative analysis methods of infrared radiation temperature field and AE variation in rock loading process. In order to describe the variation characteristics of infrared radiation temperature field quantitatively, the fractal, entropy and statistical theory were introduced and three indicators including characteristic roughness, entropy and variance were proposed to describe the variation of infrared radiation temperature field. Various AE parameters include the AE energy parameters (energy rate and cumulative energy), the AE event parameters (event count rate and cumulative event count), the b value and the entropy value were studied. Then, three rock loading experiments with thermal imaging and AE monitoring (included the hole rock in biaxial loading, rock in shearing loading and echelon model in biaxial loading) were carried on and several infrared and AE parameters were obtained. The variation and precursory characteristics of infrared and AE parameters in rock loading process were analyzed comparatively. The results showed that:1) Three infrared parameters could quantitatively describe the evolution and differentiation characteristics of infrared radiation temperature field in rock loading process effectively and the results were better than previous parameter AIRT. The infrared parameters basically showed three phases during rock loading process, included the stable phase, rising phase and accelerating rising phase, which represented the differentiation degree of infrared radiation temperature field. The characteristic roughness was sensitive to local change of temperature field. The entropy was better to describe the stage characteristics of infrared radiation in rock loading process, but its ability to identify precursors of rock failure was not as good as characteristic roughness and variance.2) Six AE parameters which could describe the AE temporal characteristics were analyzed systematically. It showed that the various AE parameters were corresponding to different features. The AE energy kept a small release in the relatively low stress phase, then increased gradually in the middle stress phase and dramatically in the high stress phase. The number of AE events were few in the low stress phase, raised rapidly in the middle stress phase and dropped greatly in the high stress phase. The b value decreased with volatility during the most rock loading process and performed an evidently decrease just before the rock failure, while, the entropy value was in reverse change trend. From the experimental results, the AE energy and event parameters could describe the stage characteristics with the development of stress, but the b value and entropy could only capture the precursors of rock failure. All the AE parameters existed the precursors of rock failure, while the entropy value occurred relatively earlier and the b value occurred relatively later. Additionally, this study showed that the precursor of rock failure would be easy to identify with the AE cumulative parameter curve.3) The infrared and AE variation features were comparatively analyzed in rock loading process. It showed that the precursors of AE parameters occurred earlier than thermal infrared parameters in all three experiments. The AE parameters were suitable for the early prediction of rock failure while the thermal infrared parameters for short term prediction. By combining the thermal imaging and AE technology could improve the reliability of precursors recognition of rock failure.The research results enrich the content of remote sensing rock mechanics and provide theoretical and experimental basis to joint monitoring of thermal infrared and AE for rock disastrous fracturing.