Deep Wet Soil Mixing Columns Ground Treatment Technique-lesson Learnt From Project

Deep Wet Soil Mixing (WSM) ground treatment columns have been designed and constructed first time on TfNSW Lisarow to Ourimbah Stage 3B project to meet performance requirements for embankment and retaining wall foundation. However, during construction, the project faces a number of challenges such as reuse of several thousand cubic meter of soil-cement mixed waste material produced from WSM construction, various quality control testing issues and construction difficulties arising from interlayered stiff/dense soil. Hence, the project team developed extensive field trials and innovative solutions to mitigate all these challenges. Instrumentation monitoring results obtained from settlement plate, inclinometer, piezometer, survey plugs and wall tags suggested that primary consolidation settlement of the WSM treated ground is virtually completed within one month after the construction. Field monitoring results also reveal that settlements and lateral movements of the bridge approach embankments and hybrid retaining wall (Reinforced Soil Wall combined with L-shaped wall) foundations are much less than the predicted design values. In addition, the trend of the 12 months monitoring results provides confidence on the long-term performance of these structures, which is expected be smaller than the predicted values. Furthermore, it is revealed that about 5000m3 of soil-cement mixed waste material/spoil have been recycled, and used successfully as fill materials for various civil engineering applications at the project site. Following the several field testing regime, it is concluded that only Unconfined Compressive Strength (UCS) testing from the cored samples is the most reliable quality control measure for high strength WSM materials. In addition, strength and deformation parameters of the field core samples are proven to be increased with the increase of curing time. Hence, it is recommended to include curing effects on the design of deep soil mixed columns ground improvement technique for future projects.