Development of design norms for rib/snook during mechanised depillaring by continuous miner

Abstract

This paper presents the efforts made to design irregular-shaped-heightened-rib/snook based on factor of safety (FOS) during mechanised extraction of already developed coal pillars by continuous miner. In situ monitoring of performance of different sizes of rib/snook with variation in their area, effective-width, width-to-height ratio and height under varying geo-mining conditions are studied comprehensively at 39 panels of 7 different mines and found a number of influencing factors affecting its design as per the field studies. Based on this study, a number of conceptual models are developed to understand the need of rib/snook and its interaction with different nature of roof at varying depth of cover. Further, a parametric study is carried out on calibrated numerical models by varying the area and height of rib/snook with nature of roof, depth of cover and panel width for the estimation of strength and stress over it. Empirical formulations are developed for estimation of a competent area, effective width and width-to-height ratio in a given geo-mining condition corresponding to a limiting value of FOS of 0.30–0.35. Further, the results of developed empirical formulations are validated with the field studies.