Abstract
Room-and-pillar mining is a commonly used mining method in previous practice in northwest China mining area. Due to priority selection of high-quality resources, coal mines in northwest China generally have to face upward mining above goaf. Thus, the stability of a floor coal pillar influenced by mining activities plays an essential role in upward mining above goaf. The results indicated that a floor coal pillar kept stable before coal excavation in the no. 6107 working face in the Yuanbaowan coal mine; however, the plastic zone in the floor coal pillar expanded sharply and the elastic core zone reduced suddenly on the influence of abutment pressure. Finally, the floor coal pillar supported failure. Accordingly, the paper proposed a floor coal pillar reinforcing technique through a grout injection filling goaf area. As physically limited by a different-height filling body on the double sides, the plastic zone scope and horizontal displacement and loading capacity of the floor coal pillar were studied, working out that the critical height of the filling body should be about 6 m which can ensure safe mining when upward mining above goaf. Case practice indicated that the fractures induced by mining in the floor coal pillar, filling body, and floor can be restrained effectively when the filling body height is 6 m, which can ensure floor coal pillar stability and safe mining of the no. 6107 working face in the Yuanbaowan coal mine. The research can provide theoretical and technical guidance for upward mining above goaf and have a critical engineering practice value.
Highlights
As the largest coal production base and a well-known demonstration project of a modern mine with production capacity over 10 million tons per year in China [1], the northwestern mining area’s coal production accounts for 68% of the coal production of the whole country according to 2018 statistics
A room-and-pillar mining method was widely used in the early stage of coal mining practice [2, 3], leaving abundant coal pillars in the goaf, which puts a huge hidden threat to the safe mining of longwall working faces of adjacent coal seams
The spatial relationship between coal pillars and the longwall working faces of adjacent coal seams is mainly divided into two types: roof coal pillars and floor coal pillars, as shown in Figures 1(a) and 1(b), which indicates that the coal pillars are located above the longwall working faces and below the longwall working faces, respectively
Summary
As the largest coal production base and a well-known demonstration project of a modern mine with production capacity over 10 million tons per year in China [1], the northwestern mining area’s coal production accounts for 68% of the coal production of the whole country according to 2018 statistics. A room-and-pillar mining method was widely used in the early stage of coal mining practice [2, 3], leaving abundant coal pillars in the goaf, which puts a huge hidden threat to the safe mining of longwall working faces of adjacent coal seams. The key to safely mining of the longwall working face above the room-and-pillar goaf is to ensure that the floor coal pillars remain stable under the influence of mining-induced stress. Feng et al considered that the failure scope of the floor strata is less than the thickness of the rock interlayers as the prerequisite for safe mining of longwall working faces, and the method for determining the feasibility of ascending mining in the strip mining area was given [22,23,24].
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