ABSTRACT
In highwall mining, pillar design (web and barrier pillars) is the key to its successful operation. Web pillar design involves three major steps viz., estimation of web pillar strength, estimation of load on web pillar and determination of factor of safety. In this chapter available coal pillar strength evaluation formulae and their adaptation to long and slender web pillars are discussed. A comparison of the available empirical techniques developed in various parts of the world is also presented with special mention to the equivalent width concept used for adapting the square pillar strength equations to long and slender web pillars. Also narrated are coupled empirical and numerical modelling techniques for estimation of load on web pillars and their safety factor evaluation to ensure safe extractions under various geomining conditions.
The chapter also presents various empirical techniques for assessment of span stability and stand-up time using rock mass classification systems, including Rock Mass Rating (RMR), modified Rock Mass Rating for Indian coal mines, Q-system (Q) and Coal Mine Roof Rating (CMRR). CSIRO-developed laminated span failure model (LSFM) is also elaborately discussed. The need for numerical modelling techniques to represent complex geomining conditions is emphasised.
