Tailings and Mine Waste Conference

Settlement and strength of clay-rich coal mine spoil Williams, David; Kho, Adrian; Daley, Andrew


The settlement of clay-rich surface coal mine spoil has three components: (i) self-weight, (ii) “collapse” on wetting up, and (iii) weathering-induced settlements. Of the self-weight settlement of initially dry spoil, about 80% occurs during placement (and is “not seen”). The remaining 20% will amount to 3% or more of the height of loose-placed spoil, at a rate decreasing exponentially with time. “Collapse” settlement of spoil on wetting up is due to “corrosion cracking” at highly-stressed particle contacts. It can amount to 10% or more of the height of loosely-placed spoil. Further saturation of the spoil will fill the voids without inducing significant further collapse. Weathering-induced spoil settlement occurs over a variable timeframe depending on the durability of the spoil. It could amount to 10% or more of the height of loosely-placed spoil. The total post-placement settlement of clay-rich spoil could amount to 20 to 30% of the loose height (20 to 30 m/100 m of height). Settlement of clay-rich spoil affects its strength and compressibility under loading, and its hydraulic conductivity. Laboratory tests carried out on as-sampled and flooded scalped clay-rich spoil from Jeebropilly Coal Mine in South East Queensland, Australia, have included material characterisation and geotechnical parameter testing. The results shed some light on the settlement and strength behaviour of these materials. [All papers were considered for technical and language appropriateness by the organizing committee.]

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