Stabilisation of tributyltin-sediment in a harbour in Helsinki

In the new Vuosaari harbour in Helsinki, an area of 75 ha tributyltin-contaminated sediment was dredged by accurate techniques and mass-stabilised in lagoons with cement. The task was completed in December 2006. The quality control and the quality assurance procedure was based on control of the hydraulic conductivity and shear strength. The settlements under the preloading phase were also carefully observed. The quality observing concept was considered together by the project owner, the geotechnical consultant and the contractor and approved by the environmental authorities. The preloading and the hardening time increased the strength significantly. The target values of the strength and the hydraulic conductivity were achieved throughout. After the removal of the preloading the stabilised layer was covered with drainage and surface layers, and with a top asphalt layer. The mass stabilisation method proved to be an environmentally and geotechnically safe application for the production of structural fill.