Mechanical properties and fracture evolution of coal rock under multistage dynamic and static loads

SUN Bo; GUO Heng; ZHANG Shurong; XU Wenyu; DOU Haoran

doi:10.13347/j.cnki.mkaq.20240423

Abstract：During the mining process of a working face,coal pillars are subjected to the combined effects of advanced support pres-sure and dynamic loads caused by periodic roof fracturing.To investigate the mechanical response and damage fracture mechanism of coal bodies under complex stress environments,dynamic and static loading mechanical tests equipped with digital image correla-tion(DIC)technology and acoustic emission monitoring were conducted.These tests examined the stress-strain behaviors and crack evolution laws of coal samples under different dynamic load amplitudes and frequencies.The research results indicate that as the amplitude of dynamic loading increases,the peak compressive strength of coal samples under static-dynamic loading conditions sig-nificantly decreases compared to the uniaxial compressive strength,with a maximum decrease of 45%.Additionally,a decrease in the frequency of dynamic loading may also lead to a further decline in sample strength.Furthermore,the study found that the elastic modulus initially increases and then decreases with the increase in the dynamic loading level,and the acoustic emission ring-down count is controlled by the amplitude and frequency of dynamic loading.Through quantitative characterization of the localization of fracture deformation in specimens using digital image correlation(DIC)technology,it was found that there are abrupt changes in loc-al dislocation and tensile displacement before macroscopic rupture of the samples.Meanwhile,the dislocation and tensile displace-ment of the localized band with the maximum principal strain exhibit different amplitude characteristics during the static and dynam-ic loading processes.