Study On Strain-Acoustic Emission Response Characteristics And Fracture Precursor Information Of Coal And Rock Under Loading And Unloading

Coal mines in my country are gradually entering the stage of deep mining,and with the increase in mine depth,rock burst disasters have become more and more serious,manifested as the increase in the number of mines and large-scale rock burst disasters that occur from time to time and are difficult to prevent,which seriously threatening the safe and efficient mining of deep coal mines.This paper uses FBG fiber grating and acoustic emission monitoring technology to test and analyze the response characteristics of coal and rock sample strain,acoustic emission count and energy during the grading cycle loading and unloading experiment,and study the coal and rock sample under the condition of loading and unloading at the laboratory scale.The damage evolution law is based on the load-unload ratio response theory to identify the strain and acoustic emission precursor information of loaded coal and rock instability.The research results provide a certain theoretical basis for studying the mechanism of rock burst and the early warning of impact damage of surrounding rock instability.The main research conclusions obtained in this thesis are as follows:(1)During the loading and unloading cycle,the internal strain change trend of the specimen has a good correspondence with the internal structure damage.In the preloading compaction stage,the original cracks and pores of the sample are gradually closed,and the internal strain shows a certain degree of increase;in the mid-loading stage,the main structure is compressed,and the internal strain tends to be stable;as the stress level continues Increase,the internal strain increase gradually becomes larger and there is a large increase before the specimen is unstable and deformed.(2)The acoustic emission signal response characteristics under different stress levels have a good correlation with the damage of the specimen.The acoustic emission count and energy response value of the sample in the early stage of loading are low,and during the stress unloading stage and the stress rising stage that does not exceed the stress peak of the previous loading stage,the acoustic emission monitoring signal appears "quiet period" phenomenon;The count and energy value increased slightly;the acoustic emission signal "quiet period" phenomenon gradually disappeared in the later stage of the load,and a dense high-value response appeared when the sample was on the verge of instability,until the sample became unstable and deformed.(3)The three indicators of peak strain,peak strain rate and cumulative strain during the specimen loading process all have obvious response characteristics.The overall strain peak showed a trend of first rising,then stabilizing and then rising.The increase in the early stage of the load was small,the mid-term strain peak tended to be stable,and there was a larger increase in the later period;the rate of change of the strain peak was higher in the early stage of the load,and declined in the mid-term,and was on the verge of loss.When it stabilizes,there will be an increase again;the cumulative strain presents an overall trend of gradual increase.The growth rate in the early stage of the load is small,the medium-term growth rate becomes larger and stable,and there is a larger increase rate in the later stage.(4)Based on the theory of load-unload response ratio,the characteristics of the load-unload response ratio of acoustic emission energy and internal strain are obtained;the overall change rate of the load-unload response ratio shows a trend of risingfluctuations in a small range-sudden increase-fall back.With the increase of the drilling angle,the coal The “sudden increase” value of the change rate of the loading and unloading response ratio of the rock sample is continuously reduced;the number of acoustic emission events is used to characterize the damage of the sample.The damage degree has increased significantly,the damage degree of coal samples has increased rapidly from 0.5 to 0.6 to 1,and the damage degree of rock samples has increased rapidly from 0.3 to 0.4 to 1,which provides a certain theoretical basis for early warning of instability damage.