Evaluating the stiffness of a cast strip for protecting a preparatory mine working

Abstract

The object of this study is the deforma-tion processes in a protective structure of the preparatory working, maintained in the excavated space of the excavation area. The task addressed was ensuring the stability of the preparatory working in a deep coal mine to improve the safety of miners and coal mining. The assessment of the strength of the cast strip for the protection of prepa-ratory workings in excavation areas has been substantiated.It was experimentally established that in the zone of active influence of mining pressure on the section 0 < l < 50 m behind the treatment face, there is an exponential dependence between the length of the work-ing l (m) and the relative change in the vol-ume δV of the protective structure. It charac-terizes the safe deformation resource of the cast strip. Within its limits, the process of gaining strength of the protective structure occurs. At δV < 0.18 and the failure rate of the arched flexible support ω< 0.2, the losses of the cross-sectional area of the working do not exceed 20 %. Under conditions when δV ≤ 0.22, the resistance of the protective structure increases, which makes it possible to limit the movement of lateral rocks on the contour of the working, ensuring its overall dimensions. In cases when δV > 0.22, and 0.22 < ω < 0.68, the losses of the cross-section-al area are more than 40 %. At a distance of l > 80 m behind the breakage face, the level of threat of roof collapses approaches a critical state, which is associated with an uncontrolled increase in lateral rock dis-placements due to the loss of strength of the cast strip.The cast strip performs the functions of a supporting structure only in a certain range of physical, mechanical, and defor-mation properties.The operational condition of the pre-paratory working is ensured within the deformation resource of the cast strip. After reaching the rated strength of the cast strip, its strength makes it possible to limit the movement of lateral rocks on the contour of the working and ensure its stability at a dis-tance of l ≤ 80 m along the length of the excavation section.