Instability And Failure Mechanism Of Coal Wall At Coalface With Up-dip Or Down-dip Mining Andits Control

Instability and failure mechanism of coal wall at coalface is one of the hot-button and difficult issues in the study of coal mine ground control. The published studies demonstrate that a stream of factors can affect the instability and failure forms of coal wall at coalface with up-dip or down-dip mining. The present studies mainly center on the field monitoring and summarization of the coal wall failure mechanism from a macroscopic perspective, with little attention being paid to the investigation of the failure mechanism from a microscopic perspective. Therefore, it is of great realistic and theoretical significance to further investigate the instability and failure mechanism of coal wall at coalface with up-dip or down-dip mining as well as its control technology. From macroscopic and microscopic perspectives, this paper investigated the instability and failure mechanism of coal wall at coalface with up-dip or down-dip mining with the hope of offering beneficial help to the understanding of the failure mechanism and control of the coal wall at coalface with up-dip or down-dip mining.Based on the plastic softening characteristics of laboratory coal specimen subjected to uniaxial or triaxial compression, this study carried out theoretical analysis to make clear the instability and failure mechanism of coal wall at coalface with up-dip or down-dip mining, employed elastic-plastic mechanics to deduce a formula for the calculation of the width of plastic zone in front coal mass, and analyzed the main factors affecting the width of the plastic zone.Numerical investigation was carried out to analyze the differences between the front abutment stress above the coal wall at coalface with horizontal mining, up-dip mining and down-dip mining. The main failure forms and failure locations of the coal wall were summarized for coalface with different mining dip angles from macroscopic and microscopic perspectives. The effect of the breakage characteristics of the rear roof strata at coalface with up-dip or down-dip mining on the stability of coal wall was elaborated. Systematic studies were conducted to investigate the effect of depth, mining height, panel advance velocity, seam strength, support resistance and mining angles on the stability of the coal wall.With the study of coal specimen containing single joint as the basis, this study investigated the effect of the joint size, location and dip angles from the perspective of deformation, failure, crack development and strength damage. The instability and failure mechanism of coal wall containing single joint or intersected by various joints and seam bedding planes was numerically studied, which shed light on the effect of various joint on stability of coal wall at coalface with up-dip or down-dip mining and uncovered the different failure characteristics of coal wall containing various joints and seam bedding planes during up-dip or down-dip mining.A technical diagram was proposed to control the stability of coal wall at coalface with up-dip or down-dip mining based on derived research results in this study. Main reasons result in the rib spalling of coal wall at coalface of Wolonghu coal mine was summarized through observing the rib spalling characteristics on the site, monitoring the front abutment stress and recording the changes of support resistance. Measures were finally proposed to control the stability of coal wall at coalface of Wolonghu coal mine.