Experimental Study On The Thermal Infrared Spectrum Variation From Deforming And Fracturing Rocks In The Loading Process

The dynamic variation of the rock stress condition is the main reason leading to the ground rock fracture and geological tectonic disaster.Compared to the conventional contact-typed and scattered stress monitoring methods,the large-scale and dynamic stress condition monitoring technology for rock could be the key point for the forecasting of geological disaster.Recently,the thermal infrared radiation(TIR)results of both the rock loading experiments and the satellite observations before earthquakes indicated that,the thermal infrared radiation variation features are different at different rock loading stages.There are 'temporal-spatial-intensity' anomaly characteristics before the rock fracture and earthquakes.The thermal infrared remote sensing technology could be an effective method for the forecasting of the disaster caused by the rock stress and the dynamic monitoring of crustal stress field.However,it remains lack of systematic and in-depth research on the variation features,wavelength features and influencing factors of thermal infrared spectral radiation in the rock loading process.This paper is supported by the National Natural Science Foundation of China 'Experimental study and mechanism research on the thermal infrared spectral radiance variation monitoring for loaded rock in the cold background'.Based on the thermal infrared spectral radiance observations,an experimental study involving the emissivity variation for loaded rock samples under outdoor conditions was conducted.The experiments yield the following results.(1)In order to consistent with that of actual satellite-based observations and to simulate an Earth observation system,the experimental system for thermal infrared spectral radiation observations for horizontal loaded rock was established in the outdoor condition.The energy components and the influencing factors of thermal infrared radiation on rock surface are analyzed theoretically.Then,the experimental conditions of the environment for thermal infrared spectral radiation observation in rock loading experiments are determined.(2)The experiments focused on the thermal infrared spectral radiance variation for the loaded rock during the elastic stage were performed.The quartz sandstone,granite and marble were selected as the experimental samples.The experimental data including the thermal infrared spectral radiance,stress,strain,temperature and the acoustic emission during the uniaxial loading process were obtained and analyzed.The variation of radiance of rocks during elastic deformation stage is revealed with the following results.Firstly,the stress change could lead to not only the temperature change,but also the spectral emissivity change.The thermal infrared spectral radiance change in the elastic stage was the comprehensive result caused by both the temperature and spectral emissivity change.Secondly,the certain waveband features for the spectral emissivity variation were the main factor leading to the sensitive waveband of spectral radiance change.The sensitive waveband of the spectral emissivity change corresponds to the RF waveband on the static emissivity spectrum.And the sensitive wavebands of the quartz sandstone,granite and the marble samples are 8.2-9.7?m,8.3?10.5?m,and 11.1?11.4?m,respectively.Thirdly,there is an obvious linear correlation between the spectral emissivity change in the sensitive waveband and the stress change.The magnitude of the spectral emissivity change was consistent with that of the strain change during the elastic stage with the magnitude of 10-5 by unit Mpa stress.(3)The variation features of the thermal infrared spectrum in the fracturing stage were analyzed with the following results when the observation surface was fractured.Firstly,the thermal infrared spectral radiance variation was the comprehensive results caused by both the temperature and spectral emissivity change as well.The waveband features for the spectral emissivity variation were the main factor leading to the sensitive waveband of spectral radiance change.Secondly,different fracturing modes can lead to different patterns of spectral emissivity change.The fracturing mode has an important influence on the radiance variation characteristics.When extensional fissures appeared on the sample surface for the three types of rock samples(quartz sandstone,granite and marble),the radiance increased considerably,with peaks in the RF waveband on the emissivity variation curve caused by the cavity effect.Thirdly,when local bulging appeared on the sample surface,the radiance decreased with certain wavelength features in the RF waveband.The diverse morphological changes related to bulging,including the factors of degree of rupture,the range of rupture area,the incline angle,can lead to complex radiance variation.(4)According to the experimental results,the factors and the internal mechanism of the temperature and spectral emissivity variation in the loading process were discussed and explained on a microscopic level.Then,the mechanisms responsible for the changes in themal infrared spectral radiance during the rock deformation and fracturing processes are discussed respectively.And the physical model related to the thermal infrared radiation variation for loaded rock was established.This study revealed the influence factors and the wavelength features of the thermal infrared spectral radiance change for loaded rocks.The experimental results could provide the experimental foundation for thermal infrared remote sensing monitoring and early warning of solid earth hazards,mine disasters and structural engineering disasters.