Background
SGME were engaged to conduct an appraisal of encapsulation, column trials, leach columns, rainfall simulation and overland flumes for a co-disposal area (CDA). The mine is an open cut operation that produces pulverised coal injection, semi-soft coking coal and thermal coal in the Bowen Basin of Central Queensland.
Objective
The mine’s CDA has been used for the disposal of coarse, fine and ultra-fine waste since 1999. Therefore, a cover is required for the CDA to ensure that it is safe, stable, non-polluting and able to sustain the nominated post-mining land use upon closure. The cover was designed using a risk-based approach and identified knowledge gaps in relation to geochemistry and erosion potential.
Solution
Phase one of the project focused on testing the geochemistry of CDA waste in leach columns to assess acid generation, salt and metal release potential in leachate.
In phase two, potential cover materials underwent erosion testing using SGME’s rainfall simulator and overland flow flumes. Rainfall simulations determined interrill erosion potential, while overland flow simulations measured rill / gully erosion potential. These simulations were essential for understanding erosion processes and sediment transport on rehabilitated land.
SGME verified preferred cover options through column trials and semi-calibrated numerical modelling. Prior to this, a conceptual cover design was developed through preliminary modelling, and material characterisations assessed soil and spoil suitability for the cover.
Matric suction and volumetric water content were measured in the column trials to produce soil water characteristic curves that were verified in SGME’s in-house laboratory. These curves were then used in calibrated numerical modelling to calculate rainfall infiltration and seepage under dry, average and wet conditions.
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