DEFINING A STRESS STATE OF A COAL SEAM SELVAGE APPLYING OUTBURST DANGER CURRENT PREDICTION METHODS

Abstract

The relevance of the research is conditioned by the demand in operational method of experimental estimation of the stress-state of a coal seam ahead of the working, which is defined by key outburst danger factors: ground pressure, gas pressure and coal strength. The main aim is to substantiate the method of estimating the stress state of a coal seam selvage in the form of ratio of current and critical values of outburst danger indicator applying simultaneously performed spectral-acoustic method and instrumental method of outburst danger current (operational) prediction. Objects: underground mine coal seams prone to dynamic phenomena. Methods: the analysis of instrumental and geophysical methods of a face space stress state control; the estimation of a stress state based on geo-mechanics of solid bodies; instrumental method of outburst danger control – on the initial speed of gas emission and cutting fines output under interval drilling of boreholes; geometric acoustics; geophysical method of outburst danger control based on spectral analysis of the drilling rig working element noise; estimation of a stress state of a coal seam selvage on the result of simultaneous control fulfilled by instrumental and geophysical methods. Results. The paper introduces the characteristics of instrumental and geophysical methods of the ground pressure control and a stress state of underground working face space, in general. It is shown that for estimating the outburst danger degree neither ground pressure value nor gas pressure value bear any importance but the ratio of current and critical values of a stress state and it is, approximately, defined by three key factors: overlaying rock pressure, in-situ gas pressure and by the strength of the most broken coal layer. The technology of defining the stress state of a coal seam, which includes interval drilling of a borehole into the wall of the working into a certain depth with the interval length of 1 meter and measuring outburst danger indicator at each interval by instrumental and geophysical methods, is substantiated. Based on the measuring results one can determine the ratio of medium values of current and critical stresses at the distance between the miller of the drillrod at the end of the current drilling of a control borehole and a geophone, installed into the wall of the working.

Keywords

• coal seam
• face space
• stress state
• current and critical values of medium stresses
• outburst danger current (operational) prediction methods