Abstract
The combined surface and underground mining method is typically used in an open-pit mine for better production and profits. However, the improved scale of mining operations at the combined mining conditions results in even more intensive strata movement and massive ground damages. This paper assesses the progressive development of the characteristics of roof movement with the longwall face advance and its influence on the ground movement at the slope area using physical models. The identification of strata zones at the combined mining conditions is also included. The results show the following: (1) the failure of the competent strong roof creates an inverse arch-shaped rock block structure, which compacts the loose rock fragments in the caved zone; (2) a bed separation occurs above the inverse structure at the top of the disturbed strata configuration and extends upward with the face advance until it approaches the continuous bending zone; (3) more intensive strata movement and ground damages are produced by the large-scale multiseam mining operations, while regular and more distinct strata zones in the disturbed configuration are identified for less intensive single-seam mining; and (4) the intensive and massive underground mining activities increase the slope strata movement at the surface mining side. This research suggests that a less intensive mining activity is preferred in the combined surface and underground mining conditions from the point of view of ground control.
Highlights
Numerical and physical modelling of the roof caving behaviours has been frequently documented in previous studies for understanding the progressive development of mining-induced fractures and mechanism of strata movement around underground openings. e models have considered the face advance rate on ground movement [8], the extension of caved and fractured zone heights [9], longwall face failure and shield-strata interactions [10,11,12], and the impact loadings on shields [13]. ese models have not considered the combined surface and underground mining method
Is paper attempts to study the influence of underground mining on both the overburden migration and the slope stability from physical models. e model configurations are selected from different geological sections of an open-pit mine. e 3 models in the work include different face dimensions: the adjacent-seam mining and multipleseam mining. e paper has three goals: (1) obtain the progressive development of roof failure and mining-induced strata movement for the combined surface and underground mining conditions; (2) identify the vertical and horizontal zones of the disturbed overburden; and (3) assess the slope behaviours influenced by the underground mining activity
Mine Description. e representative physical model in this study is based on the geological and mining conditions at the Anjialing open-pit mine, Pingshuo, Shanxi Province, where the combined surface and underground mining method is adopted for recovering the 4th and 9th seams at the mine site. e total thickness of No 4 seam is 8.6–16.8 m and averages at 13.64 m. e immediate roof above No 4 seam is sandstone with an average thickness of 7.33 m. e weak mudstone and sandy mudstone occasionally occur above the coal seam but cave in upon the face advance. e immediate roof below No 4 seam is mainly mudstone, below which is the 6.9–16.7 m thick No 9 seam averaging at 13.8 m
Summary
Precise, rapid, automatic, and continuous measurement of the strata vertical displacement above the longwall workings. E ground movement in the slope area is provided by recording the slope deformation field using the digital speckle correlation method. E camera measuring system yields more accurate strata movement results than the traditional electronic theodolite E ground movement in the slope area is provided by recording the slope deformation field using the digital speckle correlation method. e camera measuring system yields more accurate strata movement results than the traditional electronic theodolite
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