Rib Geomechanics: Its impacts in coal pillar extraction

摘要

In Bord & Pillar (B&P) depillaring, there are redistributions of mining-induced stresses on acontinual basis, primarily with apronounced effect on the natural supports - ribs and stooks. A rib need to be stable on temporary time-frame such that (a) it should provide adequate safety to men and machines during depillaring and (b) it should offer no resistance to caving, even in the worst situation when it is not 'judiciously' reduced during the retreat. The stability of ribs can be estimated through a well-known aspect ratio called factor of safety (FOS), which is the strength of ribs (S) divided by stress (P) coming over it. The strength of ribs plays a pivotal role in estimating the stability of ribs, depending on geo-mining details, sequences of extraction and related technical/managerial issues in a depillaring panel. This paper suggests a modified rib strength formulation in addition to discussing related issues. Estimation of stress on ribs using numerical modeling with rational engineering judgements and pragmatic simulations have also been briefed in this paper. Case-study of depillaring panels in eight mines, having no pronounced geotechnical problems due to rib stability, have been analysed with the formula presented in this paper.