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

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The case study describes the stabilisation of a 600 m section of a 25 m-high, 2 km-long tailings dam. Following revised ANCOLD guidance, reassessment identified an elevated risk of failure under seismic loading. The project needed to improve the dam’s factor of safety while preserving its underdrainage performance and achieving a 100-year design life. Ground investigations and 3D modelling identified a continuous organic layer beneath the embankment as a critical foundation feature.<br /><br />Early Contractor Involvement (ECI), conducted during design development from 2019 to 2024, enabled comparison and refinement of ground-improvement options. A large-scale field trial tested stone columns, confirming that 1.1 m-diameter columns were feasible and informing the final design. The selected solution combined a temporary stability buttress, stone columns, new subsurface finger drains, and a main buttress.<br /><br />Construction included 124,500 m³ of soil in the initial buttress; 6,473 stone columns, extending up to 18 m deep; 2.2 km of drainage works; and a further 225,500 m³ of soil in the main buttress. The initial buttress provided the short-term stability needed to undertake ground improvement.<br /><br />A comparative life-cycle assessment found that the stone-column design substantially reduced emissions compared with the deep soil mixing (DSM) reference design. Estimated emissions fell from 53,400 to 8,500 tonnes of CO₂-equivalent, a saving of approximately 45,000 tonnes and an 84% reduction in the project’s overall carbon footprint. Replacing cement- and steel-intensive treatment with stone was a major contributor to the reduction.

Keywords

tailings dam

stabilisation

seismic loading

stone columns

ground improvement

underdrainage

factor of safety

early contractor involvement

life-cycle assessment

carbon footprint