Rock Load Estimation in Development Galleries and Junctions for Underground Coal Mines: A CMRI-ISM Rock Mass Rating Approach

Rock mass rating (RMR) plays important role in design and selection of support system (Ghosh, 2000). For stability assessment of rock mass it is very important to know the amount of rock load mobilized around the development gallery which is estimated using RMR (Singh et al., 2003, Barton et al., 1974, Bieniawski, 1984, and Ghosh et al., 1992). In Indian coal mines, Central Mining Research Institute-Indian School of Mines rock mass rating (herein after referred to as CMRI-ISM RMR) is mostly used for formulating design guidelines for supports. In this paper an attempt has been made to correlate CMRI-ISM RMR values and rock load of galleries and junctions for different gallery widths, ranging from 3.6？m to 4.8？m, at different densities of roof rocks. The proposed empirical expression can help in quick design of support system for underground coal mines working in the same regime. 1. Introduction Roof and side falls in underground coal mines constitute the major reason for underground accidents and fatalities even today. Statistical analysis reveals that the share of roof and side falls contributes to 28.5% of the fatalities [1, 2]. After the development of CMRI-ISM RMR, an empirical approach for rock load estimation and support design in Indian underground mine roadways, the support related accidents have started declining though they still haunt the mining engineers every now and then. The RMR reflects the quality of roof in numeric terms and quantitative terms. It is based on five parameters and obtained after summation of all those five values. The obtained RMR is adjusted for different working conditions and then used to estimate the rock load mobilized around the galleries and junctions for design of support system for underground coal mines. 2. Study Area of Research Work The case studies incorporated in this paper are taken from different mines of Bharat Coking Coal Limited and Tata Steel Limited situated in Jharia coalfield (Figure 1) [3]. Jharia coalfield, located in Dhanbad district of Jharkhand state, is one of the largest coalfields in India that has been actively associated with coal mining activities for more than a century. The study area lies in the heart of Damodar valley along the north of Damodar river. The coalfield is named after the chief mining centre, Jharia, situated in the eastern part of the coalfield. The coal basin extends for about 38？km in the east-west direction and a maximum of 18？km in the north-south direction covering an area of about 450？km2. Figure 1: Location of Jharia coalfield in India. 2.1. CMRI-ISM RMR—An