Abstract
When highwall mining technology is applied to recover large amounts of residual coal left under the highwall of a big open-pit mine, a reasonable coal pillar width is required to ensure the stability of the web pillars. Using numerical simulations, this paper studied the characteristics of the abutment stress distribution in the web pillars under different slope angles and mining depths, and established a relation describing the stress distribution in the web pillar. The relationship between the abutment stress and the ultimate strength of the web pillar under different pillar widths was also analyzed. In combination with the failure characteristics of the pillar yield zone, this relationship was used to explore the instability mechanism of web pillars. Finally, the optimal retaining widths of the web pillars were determined. Based on the modeling results, a mechanical bearing model of the web pillar was established and a cusp catastrophe model of pillar-overburden was constructed. Additionally, the web pillar instability criterion was derived. By analyzing the ultimate strength of the web pillars, a formula for calculating the yield zone width either side of the pillars was established. Using the instability criterion of web pillars in highwall mining, a reasonable pillar width can be deduced theoretically, providing significant guidance on the application of highwall mining technology.
Highlights
China’s coal resources are abundant, with demonstrated coal reserves that account for approximately 11.1% of global reserves (Wang et al 2019a)
We only present the results of the stress distributions in the riskiest positions under different pillar widths and mining depths at a slope angle of 40° (Figs. 6 and 7)
Based on the distributions of positions at which the maximum abutment stress occurs, namely, the positions at which the web pillars are most vulnerable to instability, the distribution characteristics of the side abutment stress are analyzed under varying pillar widths and mining depths and at slope angles of 20°, 30°, 40°, and 50°
Summary
China’s coal resources are abundant, with demonstrated coal reserves that account for approximately 11.1% of global reserves (Wang et al 2019a). Zhang et al (2011) used the F LAC3D (Fast Lagrangian Analysis of Continua in Three Dimensions; Itasca Consulting Group Inc., Minneapolis, Minnesota, USA) numerical simulation software to systematically investigate the laws governing the stress increase coefficient of the coal pillar and the pillar’s stability. They obtained a function describing the relationships among the stress increase coefficient of the upper and lower pillars, the properties of the interstratified rock, and the geometrical parameters. Taking an open-pit coal mine in Inner Mongolia, China, as the engineering geological background, this paper systematically studies the instability mechanism and the web pillar width by means of experimental analysis, numerical simulations, and cusp catastrophe theory. Our results are expected to provide a basis for the design and safety implementation of highwall mining schemes, as well as guidance for similar projects
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