STRATA CONTROL IN WIDE STALL MINING

What is strata control? Strata refers to rock in all the possible forms such as: 1. High strength material. 2. Very low strength material(or extremely weathered). Strata control refers to the methods applied to manage the risks associated with various forms of strata instability in underground coal mines.

Wide stall mining : It is the advanced method used for optimal recovery of minerals.(eg:Coal). The conventional method of splitting and stooking of pillars have been replaced by wide stall method. Comparatively,this method is better than splitting and stooking of pillars.

Let us consider the following figure : Fig.1. Comparision of stooking and splitting of pillars and wide stall method

Necessary conditions of wide stall method: Massive immediate roof is an important requirement. If roof is moderate , reinforcement techniques such as cable bolting and roof stitching are used to avoid local deformations. Pillar strength should be more(can be done by increasing w/h ratio). Wide stall method cannot be maintained under weak/laminated roof strata.

Instruments used for strata control observations in wide stall mining: Borehole extensometer Stress meter Remote convergence indicator Photographic technique

EAST BHUGGATDIH COLLIERY The first field trial of wide stall method was conducted in EBC, situated in Jharia(Jharkhand). It was a successful attempt. It provided nearly 42% coal from a 17 m thick coal seam. No endangering of the surface and subsurface structures because of appropriate strata control measures.

Fig.2. Dimensional information for wide stall mining (sectional view) at East Bhuggatdih with a comparison to conventional splitting and stooking.

Fig.3.Top view of wide stall mining in East Bhuggatdih Colliery (Jharia)

O yeah!! Wide stall has better Safety factor. Fig.4. Comparision of wide stall and splitting and stooking of pillars(w.r.t safety factor)

Conclusion: Splitting and stooking of pillars cannot give more than 30% of coal where as, wide stall method gives about 42% of coal.(Based on Bhuggatdih colliery). The instruments used for strata control observations made the method successful. All the risks have been managed and no endangering of surface and sub surface will occur if proper strata control measures are taken.

References: Salamon MDG, Munro AH. A study of the strength of coal pillars. J. S. Afr. Inst. Mining Metall. 1967;68:55±67. Sinha PK, Verma RK, Jain DK. Research and development e€orts in thick seam mining: present and future scenario. In:Singh TN, Dhar BB, editors. Proceedings of International Symposium on Thick Seam Mining. Dhanbad, India: CMRI, 1992. p. 471±92. CMRI Report (unpublished). Field trial of wide stall mining of VII/VIII seam under built-up area at East Bhuggatdih colliery.