Abstract:
A review of a tailings storage facility embankment in New South Wales identified that historic ash deposits and organic material in the foundation beneath the embankment were potentially liquefiable, resulting in an undrained Factor of Safety (FoS) below the recommendations in the Australian National Committee on Large Dams (ANCOLD) guidelines. Stability analyses indicated a relatively high probability of failure due to seismically induced liquefaction of theses foundation soils. Through an Early Contractor Involvement (ECI) process, the dam owner engaged Menard Oceania to develop the conforming design of Deep Soil Mixed columns. In partnership with SRK Consulting, Menard/SRK carried out a comprehensive review of nine ground improvement solutions and developed a detailed three-dimensional (3D) ground model to inform an optimised alternative design utilising Stone Columns as the driving ground improvement technique. A state-of-the-art construction field trial was performed to assess the performance of Stone Column with respect to the site’ s foundation conditions. Various replacement ratios were tested, both with and without wick drains, to evaluate their effect on drainage and soil consolidation. An instrumentation system comprising vibrating wire piezometers and settlement plates was installed to monitor pore pressure and soil deformation. Post-installation in-situ testing including CPTu, PMT, CSWVT, and DMT was deployed to quantify soil strength improvements. The trial results enabled further optimisation of a Stone Column solution and provided critical insight into the impact Stone Column installation has on pore pressure generation and dissipation in the foundation layers. The alternative solution enhanced constructability and reduced foundation seepage risks through minimal impact on the foundation. The final Stone Column solution achieved an 84% reduction in carbon footprint (equivalent to 44, 806 tCO2e) compared to the initial design. Overall, the final solutions presented considerable program and cost savings for the dam owner.