Abstract
To improve the resources’ recovery ratio and the economic benefits of open-pit mines, the development of highwall mining is used to exploit residual coal. The design of rib pillar, formed by excavation and mining activities in intact coal seams, is crucial to the overall stability and safety of the highwall mining operations. This paper focuses on the damage caused to rib pillars by the large deformation, occurring with the application of highwall mining in an open-pit in China. A mechanical model was established to investigate the damaged width of colinear rib pillars based on Hoek–Brown and Mohr–Coulomb failure criterion. The equations for calculating the damaged width of the rib pillar were obtained, respectively, by combining the Hoek–Brown failure criterion with the Mohr–Coulomb failure criterion. The failure mechanism for the width of the rib pillar and the factors affecting the colinear rib pillar were analyzed in detail. The results show that the application of the Hoek–Brown criterion has a unique advantage in analyzing the damaged width of the colinear rib pillars, in open-pit highwall mining. The instability mechanism and failure process of the rib pillars are described in combination with the limiting equilibrium method and the ratio of the elastic zone’s width to the width of the entire rib pillar.
Highlights
Open-pit mining always plays a considerable role in the world’s coal mining, which has many advantages such as large output, low cost, simple mining technology, operating safety, and so on [1,2,3]. e main features of Chinese open-pit mines are the thick cover and shovel-truck mining technology system which is the most common [4, 5]
The instability mechanism of the rib pillars in open-pit highwall mining was analyzed in a simple manner. e following conclusions were drawn from this study: (1) As shown in the images captured by a borehole camera, the monitored rib pillar deformation indicates that the 4 m rib pillar was damaged completely by the coalescence of internal cracks
The calculation of the rib pillar’s damaged width was compared under different failure criteria, which further veri es the unique advantage of the Hoek–Brown criterion
Summary
Open-pit mining always plays a considerable role in the world’s coal mining, which has many advantages such as large output, low cost, simple mining technology, operating safety, and so on [1,2,3]. e main features of Chinese open-pit mines are the thick cover and shovel-truck mining technology system which is the most common [4, 5]. Many studies have investigated the stability of rib pillars based on the empirical strength equation of the Mark–Bienawski coal pillar to determine its retaining width. Erefore, it is important to investigate the differences in analyzing the damaged width of a rib pillar using either the Hoek–Brown criterion or the Mohr–Coulomb criterion. E damaged width of rib pillars was used to monitor with borehole camera exploration device (BCED) in an open-pit mine in China. The instability mechanism of rib pillars in open-pit highwall mining is explained. 3. Rib Pillar Bearing-Load Model in Highwall Mining e damage of rib pillar is a gradual failure process in open-pit highwall mining. A bearing model of the rib pillar was established according to its stress distribution characteristics during highwall mining (Figure 3). Burial depth (m) Internal frication angle φ (°) Poisson’s ration (μ) Density c (kN·m−3) Cohesive force c (MPa)
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