308 1015.7 million tonne) is being produced from the surface mines, whereas only 3% is produced from underground mines. However, despite this huge production India also imports 244 million tonne of coal from Indonesia, Australia, South Africa Russia, USA and other countries [http://Coal.gov.in]. As India shares only 2.4% land cover with 20% population in the world, availability of surface area for mining is limited. Thus, surface mining of coal deposits is difficult for the deep-seated deposits due to requirement of large surface area. Therefore, the deep-seated deposits are being mined by underground mining method. With the depletion of near-surface deposits, the production from the underground mining needs to be increased to meet the demand. Considering this mechanized excavation systems, namely shearer and continuous miner, has been deployed in the underground coal mines. Longwall shearer was first introduced in 1978 at Moonidih Colliery and Continuous miner was deployed in Anjun Hill Mine of Chirimiri Area in 2002. The continuous miner and shearer had their successful deployment in China and European coal and had studied extensively. Indian coal is predominantly drift origin and thus pose different characteristics than insitu coal (mostly available in other countries). The strength parameters are often higher in Indian coal. Therefore, a suitable cuttability index must be developed to predict the performance of the machines. In this paper, the existing performance predictive models for shearer/roadheader are reviewed and a new cuttability index for continuous miner is presented. A model is also proposed to predict the output from continuous miners using the developed cuttability index. 2. LITERATURE REVIEW Any rock cutting machine basically performed based on the rock properties, machine design and application parameters. Rock cutting machines are broadly classified into two groups – (i) cutting with point attack tool and (ii) cutting with disc cutter (Sen et al, 2000). In general, most of the cutting machines like shearer, continuous miner, road header, surface miner works with point attack cutting tool. However, Tunnel Boring Machine and some other large diameter boring machines work with disc cutting system. Point attack tools (picks) are basically mounted on a spindle or circular shaped cutting drum. On rotation of the drum, the picks hammered the rock along with a drag force provided by the movement of the boom carrying the drum. The cutting action of the point attack tool is depicted in Figure 1 (Dey and Ghose, 2008).
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