Numerical modelling-based pillar strength estimation for an increased height of extraction
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ORIGINAL PAPER
Numerical modelling-based pillar strength estimation for an increased height of extraction Ashok Kumar 1 & Rakesh Kumar 1 & Arun K. Singh 1 & Sahendra Ram 1 & Pradeep K. Singh 1 & Rajendra Singh 1
Received: 20 April 2017 / Accepted: 1 September 2017 / Published online: 20 September 2017 # Saudi Society for Geosciences 2017
Abstract Underground extraction of total thickness of a thick coal seam in single lift by bord and pillar method increases pillar height during retreat. Field studies found that the increase in pillar height affects the depillaring operation adversely, especially, during caving of the strong/massive roof strata. Dilution in strength due to the increased pillar height caused catastrophic failure of barrier pillars and goaf overriding. This warrants a systematic study of pillar strength variation for the different heights of pillar. A review of different pillar strength estimation approaches for an analysis of the dilution in strength of the heightened pillar suggested that numerical modelling provides a better option for such a systematic study. Accordingly, investigations are conducted on simulated models in laboratory adopting a recognised numerical modelling procedure. The observed nature of variations in pillar strengths with the increase in its height in the numerical models and empirical formula is found to be matched. But a mismatch is found between the strength values of the two approaches with an increase in height of the pillar. Considering validity of the empirical formulation in Indian coalfields, a relationship is developed to incorporate a correction in the strength values of the numerical models. The suggested correction on the basis of this simple study of the pillar strength variation would be helpful for the use of the established simulation tool during the depillaring of a thick coal seam.
* Ashok Kumar [email protected]
1
CSIR–Central Institute of Mining and Fuel Research, Dhanbad, Jharkhand, India
Keywords Thick coal seam . Single lift depillaring . Heightened pillar . Numerical modelling . Pillar strength
Introduction Underground extraction of the thick coal seams in India has adopted a variety of mining methods (Kumar et al. 2016) as per the existing site conditions. As per thickness of different thick coal seams, a summary of the adopted mining methods in Indian coalfields is given in Fig. 1. However, due to favourable geotechnical conditions, a large number of the thick coal seams in the country have been left developed by Bord & Pillar (B&P) method of mining. In fact, B&P is the dominant underground mining method for coal in India. Depillaring of these developed thick coal seams is challenging but important because they have locked a considerable amount of coal and blocked mining scope to the coal seams below it. Nowadays, single lift depillaring of total thickness (SLDTT) is preferred (Singh 2004; Kumar et al. 2015) over the conventional multi-section depillaring of a thick coal seam. An adoption of the SLDTT inherits the problem of strata
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