Acoustic And Electrical Precursor Response And Damage Characteristics Of Sandstone With Different Water Content Under Cyclic Loading And Unloading

Acoustic emission and electromagnetic radiation technologies have been widely used in monitoring and early warning of coal and rock dynamic disasters such as rock bursts and rock bursts.At present,the study of rock acoustic emission and electromagnetic radiation under cyclic loading and unloading rarely involves the water content of the rock,and the water has an important influence on the cracking,damage and instability of the rock.Based on this,this thesis carried out the acoustic emission and electromagnetic radiation experiments of sandstone with different water content under uniaxial cyclic loading and unloading,and studied the changes of acoustic emission and electromagnetic radiation signals of sandstone with different water content with the cyclic loading and unloading process.Multifractal theory studies the precursor characteristics of instability and failure of sandstones with different water content.Finally,the load-unload response ratio and damage theory are used to study the damage evolution process of sandstone with different water content based on acoustic emission and electromagnetic radiation signals,and the empirical formulas for damage prediction of sandstone with different water cut under cyclic unloading are established and verified.The main conclusions of the thesis are as follows:（1）Acoustic emission and electromagnetic radiation signals respond well to the sandstone cyclic loading and unloading failure process.With the increase of the number of cycles,the cumulative acoustic emission count and energy showed a step-up pattern,and the cumulative pulse and energy of electromagnetic radiation showed a wave-like rise pattern.With the increase of water content,the total number and energy of acoustic emission,and the total pulse and energy of electromagnetic radiation continue to decrease.Acoustic emission and electromagnetic radiation signals continue to weaken,but the rate of weakening continues to slow down.As the number of cycles increases,there are certain differences in the response characteristics of acoustic emission counts,energy increments,electromagnetic radiation pulses,and energy increments.The different generation mechanisms of acoustic emission and electromagnetic radiation and the presence of moisture are the main causes of the differences.（2）The sudden increase of variance²,the sudden increase of multifractal parameter?（6（6 and the sudden drop of?1）1）can be used as precursors to the failure and instability of sandstone samples.With the increase of water content,the time of the sudden increase of variance² and?（6（6 and the sudden decrease of?1）1）keep ahead,and the precursor signal is more obvious.The occurrence time of precursor is gradually advanced from the 8th cycle loading and unloading stage of dry samples to the 5th cycle loading and unloading stage of saturated samples.The acoustic emission precursor points all appear before and after the peak stress in each cycle of loading and unloading,while the precursor point of electromagnetic radiation is far away from the peak stress.（3）Compared with acoustic emission,the dispersion of electromagnetic radiation is stronger,and the volatility of the variance² is also larger.The overall regularity of the autocorrelation coefficientαis rather weak,and the variance² is more accurate than the autocorrelation coefficientαas the basis for judging the precursor signal.The acoustic emission²₈8)8)8)8)8)),(?(6（6）₈8)8)8)8)8))and（?1）1))8)₈)₈)₄)₈)4)4)4)of sandstones with different water cuts appear in the last cycle of loading and unloading,while the electromagnetic radiation²₈8)8)8)8)8)),(?(6（6）₈8)8)8)8)8))and（?1）1))8)₈)₈)₄)₈)4)4)4)except for the dry sample,the rest of the water-containing samples are all advanced.（4）With the increase of the peak stress,the load-unload response ratio and the damage variable show a steady-rapid growth pattern.The acoustic emission and electromagnetic radiation signals generated in the loading stage are more than those in the unloading stage,and the characteristic of acoustic emission is more significant than electromagnetic radiation.With the increase of water content,the corresponding peak stress gradually decreases when the load-unload response ratio and damage variable increase significantly.Through regression analysis,the empirical formulas for damage prediction of sandstone with different water content based on acoustic emission and electromagnetic radiation signals are established.Through verification,the prediction result of the empirical formula for damage prediction based on electromagnetic radiation signal is relatively high.The empirical formula can be used to calculate and predict the damage degree of sandstone with different water content under cyclic loading and unloading.The paper has 28 figures,3 tables,and 80 references.