Early Specialist Contractor Involvement Enabling Alternative Design for Sustainable Dam Stabilisation-Paper

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A tailings storage dam in New South Wales was found to have weak, potentially liquefiable foundation soils and an undrained factor of safety below Australian guidelines. The original remediation design proposed deep soil mixing (DSM), using cement-based columns to reinforce the downstream embankment. However, these low-permeability elements could increase seepage and pore-pressure risks.<br /><br />Through early contractor involvement (ECI), the dam owner, Menard Oceania and SRK Consulting reassessed the design and compared multiple ground-improvement methods. A detailed 3D ground model, built from extensive site investigations and historical records, revealed a continuous soft organic layer and informed the design evaluation. Stone columns were selected as a potentially more drainable, constructible and sustainable alternative, subject to field validation.<br /><br />A full-scale trial assessed different stone-column replacement ratios, with and without prefabricated vertical drains. Instrumentation and in-situ testing monitored pore pressures, settlement, deformation and soil-strength changes. Results confirmed that 1.1 m diameter columns could be installed and that stone columns improved strength in coarse materials without compromising the foundation’s condition. Vertical drains provided no conclusive additional benefit, so they were excluded from the final design.<br /><br />The trial enabled design refinement and gave stakeholders confidence that the alternative could meet seismic stability requirements while avoiding the drainage concerns associated with cement-based methods. A life-cycle assessment estimated emissions of 8,566 tCO₂e for the stone-column design, compared with 53,372 tCO₂e for the DSM reference design—an 84% reduction, or approximately 44,962 tCO₂e saved. The alternative also reduced material use, diesel consumption and project duration, demonstrating how early specialist input and construction trials can improve safety, cost, schedule and environmental performance.

Keywords

tailings storage dam

New South Wales

liquefiable foundation soils

deep soil mixing

stone columns

ground improvement

pore pressure

seismic stability

life-cycle assessment

carbon emissions