Document Type
Conference Paper
Publication Date
2022
Abstract
A case study of a deep-seated spoil lowwall instability controlled by a classical active- passive wedge mechanism at Anglo American Metallurgical Coal’s Dawson Mine is presented. Following a truck dump extension, widespread displacements were identified during conventional single forward pass de-coaling of Pit 6-8 strip E15. New through-spoil drilling, downhole geophysical logging, and XRD analysis identified a moisture-sensitive tuffaceous claystone unit containing a high proportion of medium-high swelling, mixed-layer illite-smectite clays 11-12 m below the lowwall floor. A novel soil mechanics approach was used to determine the mechanical properties of the tuffaceous claystone for which conventional rock mechanics tests could not be applied. Three-dimensional numerical modelling was then undertaken in FLAC3D to: a) validate the characterised mechanical properties; b) determine appropriate buttress slot widths for retreat mining of strip E16; and c) provide a validated base case for the predictive modelling and design of future strips. Operational controls for mining of strip E16 included: surface monitoring (radar, LiDAR); subsurface monitoring (TDR, VWPs); and an adaptive mine plan following the Observational Method. The TDR confirmed that the tuffaceous claystone unit at 11-12 m depth was acting as the sole basal horizon controlling the instability and mining of strip E16 was completed safely without coal sterilisation.
Publication Details
Matthew Tsang, Leonie Bradfield, Jafnie Muhsin, Ian Colbourne, Shuaibu Bun-Seisay, Hannah Kelly, Gift Makusha, Modelling and operational management of the Dawson Pit 6-8 lowwall instability, Proceedings of the 2022 Resource Operators Conference, University of Wollongong - Mining Engineering, February 2022, University of Southern Queensland, 75-95.