Analysis of the roof span stability in terms of room-and-pillar system of ore deposit mining

Abstract

Purpose. To ensure the roof span stability in terms of room-and-pillar system of mining taking into consideration the calculations, modelling, and statistic analysis of factual rock falls from the roof. Methods. Analysis of inelastic deformations to define overall displacement of a thin-layer roof of the chamber being 9 m wide was performed with the help of software complex RS2. To estimate the effect of chamber spans on the roof stability, a problem was considered in two variants where chamber width was 8 and then 7 m. The results were analyzed in terms of strength factor of the interchamber pillars. Statistic analysis of the roof stability loss for the chambers was carried out according to the results of monitoring of a state of the worked-out space in the context of the Zhaman-Aibat deposit. The obtained data were compared in terms of chamber roof spans being 9-7 m. Findings. The performed studies make it possible to state that the reduction of chamber spans down to 7 m decreases the roof deflection up to 2 cm and ensures stability of both chamber roof and worked-out space by 13 times; in its turn, that results in safe conditions while stoping. Optimal parameters of the roof span stability for chambers and safe mining conditions were substantiated basing on computer modelling and statistic analysis of the results of geotechnical monitoring of a state of worked-out space at the Zhaman-Aibat deposit. Originality. The regularity of changes in the safety factor of the peripheral part of a chamber was substantiated depending on the chamber width (7, 8, and 9 m) and considering the distance from the contoured chamber (m). Reduction of the chamber span by 1 m (from 9 to 8 m) reduces roof deflection by 2 times (up to 5 cm); moreover, breaking depth in the roof experiences considerable reduction – up to 1.75 m. Reduction of the chamber span by 1 m more (from 8 to 7 m) reduces the roof deflection up to 2 cm; breaking depth in the roof decreases considerably as well – up to 1.33 m. Practical implications. The proposed variant of chamber span reduction can decrease significantly the total area of rock falls and ensure stability of the worked-out space of the Zhomart mine where roof stability is the weakest element on the mining system. The obtained results can be the basis for the development of methodological recommendations to calculate mining parameters at the Zhaman-Aibat deposit as well as at other deposits with medium roof stability.