单轴压缩下水饱和煤样损伤演化及声发射特性研究

The low porosity and permeability characteristics of the coal have become the main bottleneck restricting the efficient extraction of coalbed methane.At present,hydraulic fracturing technology is mostly used to improve the production efficiency of coalbed methane.In this study,the representative coal samples of a lignite mine in Shanxi Province were taken as the research object.The quasi-static loading uniaxial compression test was carried out in the laboratory under dry and water-saturated conditions,and the damage evolution was analyzed.At the same time,the acoustic emission(AE)technology was used to monitor the acoustic signal induced by micro deformation and fracture process of coal samples.The three-dimensional positioning technology based on acoustic emission signal is used to characterize the micro-crack generation and propagation of the water-saturated coal sample under loading,and the amplitude characteristics and frequency distribution of the AE signal are analyzed by fast Fourier transform(FFT).The existing test results show that the compressive strength of coal samples is obviously reduced after water saturation,and the cumulative number of acoustic emission events is also reduced.The fracture process can be divided into three different stages:crack closure,crack gradually stable expansion and crack unstable development until instability.In the process of damage,the proportion of high-frequency signal will increase,the proportion of low-frequency signal will decrease,and the distribution of low-frequency band will widen and the distribution of high-frequency band will narrow.In addition,the acoustic emission amplitude is also reduced compared with the dry state.The quantitative analysis for focal mechanism of micro fracture will be conducted to illustrate the effect of water saturation on damage evolution in the future.We will probe the relation between acoustic signal and damage evaluation.This study will provide the theory for the evaluation of hydraulic fracturing,and better serve the safe mining of coal mines through the understanding of the influence of water saturation on the deformation and crack propagation process of coal and its acoustic signals.