Marine sediments in the coastal areas are often contaminated as a consequence of industrial and port activities, as well as the influence of cities located there. Construction activities and reclamation of shore line require dredging and management of contaminated sediments since the level of contamination inhibit dumping of dredged sediments into the sea. Most of these soft dredged and excavated sediments are regarded as too soft and poor quality for earth construction purposes.
Mass stabilization technology has been applied to improve the technical and environmental properties of the dredged sediment in order to utilize it as earth construction material. At the treatment sites the dredged or excavated sediments are disposed in basins, mixed with binders by mass stabilization and transported to utilization sites or left to the basins for the foundation of harbor or port area.
The technical and environmental properties of stabilized dredged and excavated soft sediments and soils have been studied thoroughly in the laboratory scale and in situ in different construction phases - in the basin before and after stabilization and in the structure after transport and construction activities. By mixing binder with mud or clay, the soil will increase its strength and modulus as the tests results show. The studied properties of stabilized soils are e.g. compression strength, modulus, settling properties, hydraulic conductivity, leaching of contaminants, etc. The workability, including the vibration resistance during transportation, has been also studied.
The high price and carbon footprint of cement binder have encouraged the use of alternative binders. Other used binder materials include fly ash and end product of desulphurization from combustion of coal and oil shale. The leaching test results show that heavy metal leaching is very low with all binder materials tested. During the mass stabilization application process, it was observed that the great water content has a considerable impact on the amount of cement required as binding agent. It has been notised that it is possible to obtain higher strength and better homogeneity by mixing fly ash (and FGD) to low amount of cement (or lime) or to use oil shale ash alone as a binder. Those mass stabilized sediments have been utilized as earth construction material in various construction sites of the Helsinki city area such as in parks, noise barriers, closing of old landfills and in harbors. In the park and landfill cases the stabilized soil has been used as a filling material of landscaping hills. In the high and steep sloped noise barrier stabilized soil have been used as embankment construction material. In harbors the stabilized sediments have been utilized as filling material.
Lessons learnt from practical projects , Monitoring and long term performance, both technical and environmental
