Study on variation law and mechanism of coal potential signal with different lithology

The potential signal generated in the process of coal rock deformation and failure can better characterize the damage evolution process of coal rock, and has a good application prospect in the field of coal rock dynamic disaster monitoring and early warning. At present, most of the researches focus on the potential characteristics and laws of the same type of coal rock failure, and there is a lack of systematic research on the comparative analysis of potential characteristics of different types of coal rocks. At the same time, there are few comparative studies on the effect of different lithology coal rock structure failure process and components on the surface potential signal generation mechanism at the micro level. In order to deeply study the response law and difference of potential signal of coal and rock with different lithology, four kinds of samples, graphite, raw coal, sandstone and granite, are selected for uniaxial loading and the potential signals generated in the process of damage and failure are collected synchronously. The variation characteristics of potential signals of four samples under loading and failure are analyzed. The results show that the potential signal value of graphite sample is relatively low, and the potential signal fluctuates greatly during the crack damage and unstable crack propagation stages. The fluctuation of the potential signal of the raw coal sample is consistent with the fluctuation of the load, and the variation of the overall potential signal is relatively stable. The potential signal value of the sandstone sample increases rapidly in the compaction stage and the elastic deformation stage. The potential signal of the granite sample fluctuates greatly in the crack damage and unstable crack propagation stages, and the potential signal value increases faster. By scanning electron microscope and X-ray fluorescence spectrometer, the generation mechanism of potential signals of coal samples with different lithology is explained from the aspects of microstructure and components. The results show that there are more mylonic scratches from the microscopic point of view in the graphite and raw coal samples in the compaction and elastic deformation stages of coal rock loading, which indicates that the friction effect is the important reason for the electrification of the graphite and raw coal samples. The sandstone and granite samples contain more O and Si elements, and the piezoelectric effect is the key reason for the electrification of the sandstone and granite samples, and the potential signal of the sandstone sample is more affected by the piezoelectric effect. In the crack initiation and stable crack growth stage, crack damage and unstable crack propagation and unloading stage, the potential signal generation of each coal sample is mainly caused by the crack propagation and friction effect inside the sample. Among them, crack propagation is an important reason for the generation of coal-rock potential signals. The charge separation at the crack tip mainly includes three aspects, including electron escape caused by stress concentration at the crack tip, crack surface charge separation caused by crack propagation and crack tip discharge

Energy Dissipation and Electromagnetic Radiation Response of Sandstone Samples with a Pre-Existing Crack of Various Inclinations under an Impact Load

Various primary fissures and defects are widely present in a rock mass and have a significant impact on the stability of the rock mass. We studied the influence of the crack inclination angle on the energy dissipation and electromagnetic radiation (EMR) response of sandstone under an impact load. Impact tests were conducted on red sandstone samples with different inclination angles, in addition to test energy dissipation and EMR signals. The results showed that as the energy of the stress wave increased, the energy consumption density and damage variables of the sample gradually increased, and the electromagnetic radiation energy also increased. As the crack inclination increased, the energy consumption density first decreased and then increased, while the damage variable and electromagnetic radiation energy first increased and then decreased. In the process of impact damage, the main frequency of EMR was 0~5 kHz. As the energy of the stress wave increased, the dominant frequency band of the main frequency expanded from low frequency to high frequency, and the amplitude signal gradually increased; the α = 45° specimen frequency domain was the widest, and the amplitude was the largest. The crack inclination significantly changed the failure state of the sample, resulting in changes in the energy dissipation and the electromagnetic radiation response of the sample

Analytical Damage Model for Predicting Coal Failure Stresses by Utilizing Acoustic Emission

Overburden collapse and water inrush in mines are primarily caused by rock fractures. Mining safety can be enhanced by monitoring and identifying early signs of coal failure in the mines. This article collected acoustic emission data synchronously throughout a series of uniaxial compression (UC) experiments on natural and water-saturated coal. The influence mechanisms of water, mechanical properties, and acoustic emission signals on the stress–strain curve and the SEM results of water-saturated and dry samples are investigated. As a result, the mechanical properties of coal are not only weakened by water saturation, such as elastic modulus, strain, stress, and compressive strength but also reduced acoustic emissions. In comparison with saturated coal, natural coal has a uniaxial stress of 13.55 MPa and an elastic modulus of 1.245 GPa, while saturated coal has a stress of 8.21 MPa and an elastic modulus of 0.813 GPa. Intergranular fractures are more likely to occur in coal with a high water content, whereas transgranular fractures are less likely to occur in coal with a high water content. An innovative and unique statistical model of coal damage under uniaxial loading has been developed by analyzing the acoustic emission data. Since this technique takes into account the compaction stage, models based on this technique were found to be superior to those based on lognormal or Weibull distributions. A correlation coefficient of greater than 0.956 exists between the piecewise constitutive model and the experimental curve. Statistical damage constitutive models for coal are compatible with this model. Additionally, the model can precisely forecast the stress associated with both natural and saturated coal and can be useful in the prevention of rock-coal disasters in water conditions