Innovative SSP Design and Construction for a Complex Soil Remediation Project-Paper

Paper

Pdf Summary

The final phase of remediation at Victoria’s former Rock Bay coal-gasification site required removal of about 90,000 tonnes of contaminated shoreline and bay soils. Because much of the material was submerged, the bay had to be sealed and dewatered while two large stormwater outfalls remained operational. Excavation also had to reach property boundaries without encroaching on neighbouring land.<br /><br />Isherwood Geostructural Engineers designed a temporary steel sheet-pile bin wall to retain the water and perimeter shoring for excavations up to roughly 12 m deep. The original plan included internally braced cofferdams along the south boundary, but installation encountered unexpected controlled-density fill and stronger-than-anticipated clay, causing delays. The team revised the scheme, eliminating three cofferdams and using raked struts supported by sheet-pile buttresses. Monitoring showed the soils and shoring performed better than expected, allowing a lower level of bracing to be removed.<br /><br />Unexpectedly high bedrock beneath part of the bin wall also reduced the piles’ available passive resistance. After probing the rock profile, the engineers designed grouted steel toe pins to connect the sheet piles to bedrock. Both stormwater outfalls were diverted through large steel pipes and discharged beyond the barrier.<br /><br />The bay was dewatered beginning in March 2015. Inclinometer readings tracked bin-wall movement as water pressure increased, enabling the team to add granular berm support proactively. Low groundwater recharge made dewatering relatively straightforward.<br /><br />The project’s changing ground conditions, tight schedule, and strict boundary constraints demanded frequent coordination and design adaptation. The observational approach, close monitoring, and supplementary field investigation helped the team respond to unexpected conditions, maintain progress, and avoid unnecessary construction costs.

Keywords

Rock Bay

remediation

contaminated soils

shoreline excavation

temporary sheet-pile wall

dewatering

stormwater outfalls

bedrock conditions

grouted steel toe pins

observational geotechnical design