Performance evaluation by advanced in-situ instrumentation and monitoring
Optimisation of safety and recovery during underground coal mining involves a number of measurement, instrumentation and monitoring. Generally, the efforts to project likely rock behaviour in advance by theoretical analysis and modeling do not yield reliable results. This happens because the characteristics of the surrounding rock mass in a real structure is different from the usual theoretical assumptions. The depositional condition of the site plays an important role in estimating the performance of mining structures. This is the reason why most of the strata control norms are based on empirical formulations. These empirical formulations require quite dense (in time and space) field measurements of different strata control parameters.
The department found itself always engaged in visualising the suitability/performance of different imported mining technologies to our industry. Under this scheme, the department worked with Russians, British, South African and French in Indian coalfields under following projects:
Strata Behaviour study at Country’s first fully mechanised depillaring face deploying Continuous Miner & Shuttle Car at Anjan Hill Mine, in close collaboration with SECL (India), Joy Mining (South Africa), Rock Mechanics Technology (UK) and CMRI
Numerical model based study for the stability of parting between Top and bottom sections of Zero seam at Chirimiri colliery, in close collaboration with Joy Mining Machinery formerly Gullick Equipment Ltd., UK and CMRI
Development of machine vision based (using CCD and laser projection) system for automation of mining measurements, during study leave work at the Department of Geomatic Engineering (University College London) and CMRI.
Geo-technical Evaluation of mechanised longwall soutirage face of East Katras Colliery, in close collaboration with Cdf, France and CMRI.
Strata control observations and performance monitoring of flexible roofing and self descending sectional shield (C K Shield) for the extraction of top and bottom sections respectively of 60 ft. seam at Tipong colliery, Assam, in close collaboration with USSR and CMRI.
Performance evaluation of foreign mining technologies under Indian geo-mining conditions involved extensive in situ monitoring, in addition to study on simulated numerical & physical models. On the basis of these studies following important conclusions were drawn:
These investigations revealed that the design norms for underground coal mining of Europe are not suitable for Indian mines, mainly due to difference in geological origin.
Indirect increase of void height (during mechanised sublevel caving of a thick seam) must be considered for support density estimation of our coal fields due to low bulking factor of the rock mass.
Stiff roof bolts (synthetic bonding) can effectively be used as breaker line at goaf edge due naturally favourable stress redistribution around the working face.
Dynamic loading of the descending sectional shield should be considered during design of its rating
Increased stiffness of natural support by staggered bottom section development during single lift working of complete thickness of a thick coal seam (consisting developed pillars along roof horizon) by BG method arrests the chance of goaf overriding.
In addition to these significant observations, the performance evaluation process also customized the imported design in the best techno-economical interest of the industry. For example, the initial design of breaker line support by Joy Mining (South Africa) consisted three rows of bolts. The performance monitoring (study of load distributions along the roof bolts of different rows of the breaker line) in the first panel (Pane-C, Anjan Hill Mine, SECL) of the mine found only two row of bolts can serve the purpose, which has successfully been practiced in the second panel (Panel-B) of the mine. Reduction in one rows of bolts from the original design of the breaker line support saved millions of rupees of the industry in each panel.
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[1] Sheorey, P. R., Das, M. N., Barat, D., Prasad, R. K. and Singh, B., 1987. Coal pillar strength estimation from failed and stable cases. International Journal of Rock mechanics and Mining Sciences, 24: 347-355.