Study On Infrasound Response Characteristics And Cascade Rupture Mechanism Of Coal And Gas Outburst

Coal and gas outburst is a common gas-driven disaster in underground coal mining,which is characterized by the continuous instability and rupture of the coal-rock system in a very short period of time,mixed with high-pressure gas and violently ejected into the mining space.As China gradually enters deep resource mining,the possibility of encountering outburst disasters is also increasing.What energy principle does the outburst process follow? Are there detectable characteristic signals before the outburst occurs? How does it develop rapidly after the outburst occurs? These questions are important issues related to the prevention and control of outburst disasters.Although the outburst mechanism has been widely studied in the past few decades,the answers to these questions are still not clear.The aim of this dissertation is to expand the understanding of coal and gas outbursts by exploring new technologies and methods.The dissertation investigates the infrasound response characteristics and cascade rupture mechanism of coal and gas outbursts as the central research topic.The study combines infrasound detection and physical simulation experiments,utilizing interdisciplinary research methods such as rock mechanics,fluid mechanics,volcanology,and geophysics.Mathematical analysis methods such as Fourier analysis,signal analysis,and cross-correlation analysis are applied to explore the energy principle of the outburst,the infrasound response during the outburst process,and the physical mechanism of rapid propagation.As a result,the pressure oscillation model and cascade fracture model are constructed.These findings enhance our understanding of the outburst mechanism and offer novel perspectives for future prevention work.The main research conclusions of this dissertation are as follows:The occurrence of coal and gas outbursts is primarily caused by the increased expansion of local gas resulting from stress release.Through a comprehensive analysis of simulation experiments and field observations,coupled with energy analysis,the stress-gas coupling mechanism in the outburst triggering stage has been explored.It has been pointed out that the sufficient condition for outburst occurrence is the presence of adequate free gas stored in coal pores,which requires stress release to create sufficient fracture space in the local area.The analysis indicates that,under appropriate physical conditions,the crack area caused by stress release will continue to develop,accompanied by the continuous growth of gas expansion energy,until it reaches the energy threshold for triggering an outburst.The outburst-triggering process is a critical process that generates precursor signals and causes the "delayed" characteristics of the outburst.The decisive impact of adsorbed gas potential on outburst development is revealed.Based on outburst simulation experiments,the energy sources and consumption during the outburst process are estimated,and it is proved that the adsorbed gas potential is the main driving force of the outburst process,which can significantly increase the total energy of the outburst(1.35～2.95 times).At the same time,adsorbed gas will also have a systematic impact on the development of outbursts,including increasing the strength and distance of outburst,slowing down the rate of gas pressure decline(reducing by1/3～2/3),resulting in longer outburst duration(increasing by 1.37～2.71 times),increasing the propagation speed of outburst front,and determining the formation and range of layer fracture.The infrasound response generated by local gas accumulation is discovered and the outburst triggering-infrasound response mechanism is proposed.Using the selfdesigned infrasound detection system and combined with physical simulation experiments,the periodic infrasound response during local gas accumulation is discovered.The theoretical derivation proves that the gas accumulation zone will have spontaneous pressure oscillation under the driving of continuous gas inflow,thus generating infrasonic signals.Further analysis shows that the dominant frequency of triggering-infrasound response will experience different degrees of frequency shift(in the range of 0.5～8 Hz)due to changes in different physical parameters.This characteristic can be used as a reference for judging the triggering state of the outburst.The study of infrasound generated during coal and gas outburst processes has revealed key waveform characteristics and led to the development of an algorithm for analyzing these signals.By combining an infrasound detection system with an outburst simulation system,researchers were able to observe the infrasound waveforms generated during the outburst process.The waveforms were found to consist of a highpressure infrasound pulse followed by a low-pressure tail sound.Using crosscorrelation analysis,the results demonstrated a high degree of correlation between these infrasound waveforms,providing insight into the self-similar growth characteristics of outburst development.The proposed algorithm for analyzing the amplitude sequence of infrasound signals was found to offer a more accurate estimation of outburst intensity.The algorithm also revealed a stepwise increase in the (9(),which is indicative of cascade development and can be used to study the outburst development process.The proposed cascade rupture mechanism for coal and gas outburst development provides a theoretical foundation for understanding the rapid development of outburst phenomena.The self-similar cascade growth of the outburst process is characterized by an energy-positive feedback mechanism,which involves rupture,energy supply,triggering larger ruptures,and obtaining more energy supply.Furthermore,a cascade rupture model has been constructed for simulating the rapid development process of outbursts.The model shows that continuous cascade processes can lead to an exponential increase in the rupture range,which ultimately results in the outburst entering a rapid development stage.The results of the model demonstrate that under appropriate energy conditions,even an initial small outburst can rapidly develop into a large-scale dynamic phenomenon through a continuous cascade.This dissertation has 125 figures,23 tables and 276 references.