Concrete injection column ground treatment design within a brownfield site with compressible soils

Concrete Injection Columns (CICs) are commonly used in geotechnical ground treatment to meet serviceability and stability design criteria. Together with a load transfer platform, the design objectives are achieved by bridging future fills across existing fills and soft materials to transfer loads from a higher level to a stronger underlying material layer. Efficient CIC design within brownfield sites can be challenging when there is high variability or uncertainty in the depths and extents of existing fills and soft materials. This case study presents the CIC ground treatment design development and validation required to support the future rail earthworks platform for the Sydney Metro West – Western Tunnelling Package Clyde Stabling & Maintenance Facility (SMF). The selected performance based geotechnical ground treatment design comprised 0.45m diameter CICs at typical 2m centre to centre (c/c) spacings to overcome the risk of excessive site wide settlements and meet the project settlement criteria. Validation included a CIC installation trial to calibrate CIC rig torque readings intersecting soft materials and a static load test to demonstrate CIC settlement performance in line with predicted settlement behaviour, reducing uncertainty in the installation methodology and production CIC performance prior to construction.