Evaluation of Strata Behaviour and Goaf Atmosphere in Thick Seam Mining - A Case Studies

Abstract

This paper presents overview of strata behaviour in thick seams extracted by Blasting Gallery (BG) method of underground mining. After few years of discontinuance of blasting gallery method due to spontaneous heating and loss of considerable coal in goaf, the mehtod was reintroduced in typical underground mine – GDK-11 of SCCL Salient results of strata monitoring along with evaluaiton of goaf atmosphere are presented besides few cases of strata monitoring studied over three decades by the first author. Compilation of performance of all the BG workings in various mines of Godavari Valley coalfield would also be useful for understanding the caving behavior and strata mechanics at different stages of extraction with due regard to optimization of panel size, area of extraction etc. so as to minimize the chances of Fire and spontaneous heating of coal. Overview of performance of previous BG panels at GDK 10, and cavability of roof indicated that in near future, BG panels may be planned with panel sizes of about 120x120 m, so that the major fall with adequate span may occur at an area of about 8000 m2. This size of panel may minimize the chances of premature sealing/closure of panels reducing chances of fires/spontaneous heating in subsequent BG panels besides goaf treatment with inert gas. Different ratios related to evaluation of goaf atmosphere shows different status in which Graham’s ratio (GR),Young’s ratio (YR), Jones and trickett ratio (JTR) and CO/CO2 Ratio shows no sign of heating, Active Fire, coal dust Explosion and no sign of heating respectively indicating the need of further evaluation of the ratios with meticulous monitoring of goaf atmosphere through various continuous gas real time monitoring systems including Wireless sensor communication systems for understanding the status of fire.