Kemp, A, Russell, C & Keith, A 2014, 'Stream diversion and reinstatement on a mine backfill in tropical Borneo', in Y Potvin & T Grice (eds), Proceedings of the Eleventh International Symposium on Mining with Backfill
, Australian Centre for Geomechanics, Perth, pp. 503-516, https://doi.org/10.36487/ACG_rep/1404_41_Keith
The island of Borneo, of volcanic origin and lying astride the equator, presented the challenges of tropical wet seasons and volcanic soil to the relocation of a river to access coal seams, and subsequent reinstatement over the backfilled pit.
Working together, the mining contractor and engineers developed a robust approach to accessing over 1 m t of coal that would otherwise have been sterilised by the river running over the seam. The process involved a staged approach including cutting off a river meander and training the river to maximise pit extent on the southern side of the river, relocation of the river through a large cutting to the north to mine under the original riverbed, backfill of the southern pit and reinstatement of the river similar to its original alignment on the mine backfill.
The river diversion and reinstatement presented numerous significant technical and social challenges. The tropical location meant even the dry seasons often had significant volumes of rainfall for the river to drain to the Java Sea, hampering earthworks, while the wet seasons saw considerable water flows and flooding having to be handled by the river in its various configurations. Borneo’s geology is such that the local mine overburden material is not well suited to producing competent compacted earthworks. This meant regular importation of suitable material from Sulewesi at high cost for construction projects. Finally, the local indigenous community made use of the river as a water source and transport route, requiring attention to meeting their needs through all stages of the relocation and reinstatement.
The adopted solution utilised the contractor’s expertise in getting the most out of the mine overburden and local material for earthworks construction combined with engineering hydraulic, geomorphology and geotechnical expertise. Working collaboratively, the combined expertise produced a low cost design to address the key risks of settlement, seepage, safety of adjacent open mine pit after reinstatement and changes to the river hydraulic gradient causing sediment regime changes and river scour. The final design, while maximising the use of uncontrolled backfill of the pit, used a limited thickness compacted mine overburden liner and an alignment and cross section that enabled the river to find its own alignment over time, but constrained it within limits to protect the adjacent pit. The provision of revegetation for the final alignment reinstated historic river amenity.
Now, some four years after construction of the backfill and river reinstatement, the design has proved effective in achieving the aims of managing these risks and achieving a safe and robust outcome, sensitive to the post-mining environment and the local community.
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