Importance of Fracturing Hard and Massive Overlying Strata for Complete Extraction of Thick Coal Seam – Case Studies

Abstract

Engineering efforts need to be organized as per the rock mechanic conditions of the site for efficient underground extraction of a thick coal seam. Geo-mining conditions of Indian coalfields have favoured development of thick coal seams on Bord and Pillar (B&P) method, where single lift depillaring of total thickness (SLDTT) is vital for their final extraction. Competency of heightened pillar is an important factor for uncontrolled roof-pillar interaction during caving of the hard and massive overlying strata. An increase in extraction height by underwinning of roof coal band of the thick coal seam during retreat, developed along its floor horizon, is found to be the main reason for the strength deterioration. Conducted field studies also showed that the presence of competent overlying strata caused caving after a large overhang inside the goaf varying from 6000 m2 to 12500 m2. An attempt was made to control the roof caving by a proportional increase in width of the heightened pillars and it worked well but caused the issue of resource conservation. However, another field study with SLDTT working below laminated and weak overlying strata experienced a smooth strata control condition. This fortifies the idea of strength reduction of the competent overlying strata by fracturing for a controlled strata behaviour. This paper presents the result of the field investigations to demonstrate the role of strength reduction of overlying strata for underground extraction of total thickness of a thick coal seam in single lift.

Precise detection of coal and gangue based on natural γ-ray

“…The fully mechanized longwall top coal caving (LTCC) mining technology is one of the main technologies used for mining thick seams 4 – 7 . Improper timing of the caving-opening closure in the caving process of the LTCC mining face can result in excessive or insufficient caving, leading to resource wastage or compromising coal quality 8 , 9 . Reasonable time for closing the caving-opening depends on the mixing degree of coal gangue 10 – 12 .…”

The Precise Detection Technology of Coal and Gangue Based on Natural γ-Ray

“…The fully mechanized top coal caving mining technology is one of the main technologies for thick seam mining [4][5][6] . The unreasonable caving outlet closing time in the caving process of the fully mechanized top coal caving mining face will lead to over caving or less caving, and then waste resources or affect the coal quality 7,8 . The reasonable caving outlet closing time is determined by the coal gangue mixing degree [9][10][11] .…”