Remediation of contaminated marine sediments using mudcrete – a case history

Remediation of the second-highest priority contaminated site in New Zealand has provided an opportunity to remove and stabilise contaminated marine sediments from the Calwell Slipway Basin, Port Nelson. Other drivers for the project included restoring navigability and extending an existing reclamation. The new reclamation was constructed with dredged marine sediments mixed with Portland cement and powder activated carbon to create mudcrete. The addition of cement and powder activated carbon increases the strength of the sediments and minimises leaching of contaminants. Environmental and engineering design components are discussed including results of the laboratory bench trial undertaken to determine appropriate dosage rates, full-scale production trials, and results achieved during construction. Geotechnical design was governed by seismic loading and the need to mitigate liquefaction of the existing reclamation fill and marine sediments beneath the mudcrete.