A safe depillaring design for shallow depth of cover with influence of surface ground movements: a study in Jharia Coalf
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ORIGINAL PAPER
A safe depillaring design for shallow depth of cover with influence of surface ground movements: a study in Jharia Coalfield Amar Prakash 1 & Niraj Kumar 1 & Dilip Kumbhakar 1 & Ajoy K. Singh 1 & Avinash Paul 1 Received: 5 May 2017 / Accepted: 27 March 2018 # Saudi Society for Geosciences 2018
Abstract Extraction of coal from a shallow depth of cover especially under multi-seam mining condition requires intensive precautions in respect to safe working and impact on surface structures. A detailed geotechnical investigation is imperative for the design of a suitable support system during depillaring operation. A study has been exercised in Maheshpur colliery of Jharia Coalfield to assess the stability between the parting of VIIIA and VIIIB seams through numerical modeling. The support systems have been framed for split galleries, slices, and goaf edges with the help of well-established Central Mining Research Institute-Indian School of Mines rock mass rating (CMRI-ISM RMR) and NGI-Q system. A suitable method of depillaring has been designed keeping in view the safety of surface structures in respect to subsidence. Keywords RMR . RQD . Rock load . Support design . Subsidence
Introduction Control of strata movement is one of the vital thrust areas for safe workings in underground mines. Roof fall generally takes place due to detachment of lower strata since the process of redistribution of stresses takes place around the excavation made. Around 61.1% of the incidences are due to roof fall, which accounted for 28.5% of total fatalities (Sinha et al. 2003). Thus, a proper support design of mine opening is essential for the stability of the roof and safe workings (Anon. 1990). Surface subsidence from underground mining activity is an unavoidable problem. Surface subsidence is an important environmental consideration for active mine operations. It is an inevitable consequence of underground mining—it may be small and localized or extend over large areas; it may be immediate or delayed for many years as stated in SME (Hartman 1992). The sickle-shaped Jharia Coalfield occupies an area of about 453.24 km2, extending for a maximum about 38 km east-west and 19 km north-south and is located in Dhanbad * Amar Prakash [email protected] 1
CSIR-Central Institute of Mining & Fuel Research, Dhanbad 826015, India
district of Jharkhand state (Singh 2007). Maheshpur colliery is located at Govindpur area of Jharia Coalfield. A panel “C” in VIIIA seam, located at an average depth of 54 m and having a dimension of 160 m × 105 m, is proposed to be extracted by room and pillar method. A panel in the overlying VIIIB seam having a parting of 12 m from VIIIA seam was depillared with caving as shown in Fig. 1. The topmost IX/X seam, partly extracted by opencast method above the proposed panel “C,” was filled with overburden dump up to a height of 20 m above the surface. The subsidence study was also carried out to assess the safety of the surface structures.
Geotechnical parameters The immediate roof above VIIIA seam was
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