Slope stability analysis of open pit highwall mining excavations - A parametric study
Highwall mining operation involves driving a series of parallel unsupported, unmanned and unventilated excavations into a coal seam exposed at the open pit Highwall using a remotely operated continuous miner with attached conveying system. These parallel excavations are separated by web pillars of pre-designed width which are critical to the Highwall mining operations. The Highwall slope must remain stable during Highwall mining operation to ensure safety of workers and machinery. In this paper, Highwall slope stability is investigated with respect to different Highwall mining parameters using FLAC3D numerical modeling software. The parameters included in the study are: (i) single seam and multiple seams Highwall mining excavations with different width to height ratios; (ii) different Slope angles; (iii) different excavation heights; and (iv) different cover depths. A narrow strip of rock mass is considered by taking a plane of symmetry. The modeling results reveal that stability of open pit slopes have profound influence on the Highwall mining parameters, and the web pillar design can affect the stability of Highwall slopes. In designing Highwall slopes for an open pit, the design must include Highwall mining excavations, otherwise, near critical failure slopes could become critical and fail with Highwall excavations. In authors' knowledge, this work is the first attempt at exploring the effect of Highwall mining parameters on overall slope stability.