Due to human activities, often related to different types of industrial enterprises, soil and sediments have been contaminated. In earlier years the contributions were larger than today, but still the use of environmental hazardous substances such as PCB (Polychlorinated Biphenyl), PAH TBT (Polycyclic Aromatic Hydrocarbon TBT) and inorganic compounds such as cadmium, led and mercury are contaminating our environment and have to be handled to reduce environmental risks. Shipping, which utilises fairways in waters and harbours, needs to dredge periodically as a result of natural sedimentation and increasing sizes of vessels and development of their activities.
The predominant method for the treatment of contaminated soil/sediments is removal. The conventional method of handling dredged material is to dump it further out to sea, deposit it in bays inside levees or at inland deposits. The stabilisation/solidification (S/S) method is based on immobilisation of contaminants by chemical fixation, solidification and/or chemical reaction. The mobility of the contaminants is substantially reduced and hence their influence on the surroundings is reduced. From a geotechnical point of view, the S/S method increases the strength of the material and improves its deformation properties and its durability. As a result, S/S treated contaminated sediments and dredged material can be used for areas on land or harbour activities and other applications. Disposal at sea has formerly been the common solution but as dredged material has been found to be contaminated this solution will be used only in exceptional cases due to demands from authorities so as to secure the waters. The disposal at landfills is very costly, thus making the S/S method an economically competitive solution. Furthermore a frequent use of the S/S method is likely to enable more contaminated sites to be treated, providing society with a better built environment and thus preventing the environment/waters being contaminated further.
The project will develop the stabilisation/solidification method so that those responsible for harbours and other areas with contaminated sediments and other dredged materials can analyse and apply the S/S method as an alternative to the current solutions.
The overall objectives of the project are to develop and commercialise new services and products related to the S/S method. To achieve this, the project will develop the S/S method for:
- Greater understanding of the basic behaviour of S/S treated contaminated sediments with respect to geotechnical and environmental properties, including long-term properties and durability.
- Use of appropriate binders for various matrices of sediments-contaminants.
- Developing cost-efficient mixing techniques and improvement of the mass stabilisation technique.
- Establishing principles for the design and construction of geotechnical structures using S/S treated sediments.
- Developing a methodology for assessment of different solutions aimed at providing guidelines for permit applications.
The project is cross-national and consists of a Norwegian part and a Swedish part. The two parts are designed to be complementary, adding more value to all partners at lower cost and more quickly. The project shall be implemented in a number of different work packages. In each respective work package, WP, there are usually inventory, literature studies, laboratory trials/field studies and evaluation and synthetic work, together with reporting. Below is a brief summary of the various work packages which are implemented in the project. Coordination between the various WPs and within the respective work packages will be carried out through a project organisation which makes the exchange of information and experience possible. Reporting back on results will be performed in a number of deliverables. The project as a whole will gather together experts in chemistry, environmental engineering, geotechnical engineering, harbour engineering, risk and sustainability assessment, construction work and deep mixing technologies. The research organisations will cooperate with producers of binders, consultants, contractors and harbours. The project outcome will be tested and analysed in pilot projects in order to ensure the eligibility of the results.
WP1, Basic behaviour of the S/S matrix
The objective of WP1 is to study the basic reactions and processes in the matrix sediment-contaminant-binder which govern the magnitude of leakage, permeability and strength of the treated sediments, focusing on conditions in harbours and on organic contents and both non-organic and organic contaminants in the sediments. Also, the durability of the treated sediments is extremely important.
The goal is to present the basic behaviour of contaminated sediments and dredge materials treated by the S/S method, to create a basis for a reliable, sustainable use of the method.
WP2, Binders and additives
WP2 aims to investigate different kinds of binder and additive that can be used in order to find the most suitable mixture for typical Swedish sediment conditions. The main focus will be to find suitable mixes of binders that are satisfactory, even though the sediment might be inhomogeneous. The amount of binder that needs to be added to ensure optimal stabilisation and solidification will also be investigated. The goal of this work package is to be able to deliver a database that will make it easier for those responsible for harbours and other places to choose the right binder and additive for their particular sediment.
WP3, Geotechnical structures and premixing
This work package aims to develop principles for the design and construction of geotechnical structures, using S/S treated sediments, to be used for typical harbour activities. Anticipated uses of the geotechnical structures that may be built are paved areas for vehicles, for the loading and reloading of containers and different types of goods, and offices, industrial buildings and buildings for storing goods.
The goal of the work package is to establish a set of typical solutions and thereby provide support for future design and construction activities. This work package will also consider the situation in which new, different types of binder need to be mixed. This mixing needs be carried out to achieve the right quality and cost effective distribution. The mixing technique and logistics need to be developed further and best practice needs to be established.
WP4, Assessment of alternatives
There are various options for managing sediments from dredging in harbour areas. From a decision-making perspective, all feasible alternatives should be considered and compared as regards legislative, economical, technical and environmental aspects. This work package aims at developing support for decision making, for example, guidelines on environmental impact, life cycle costs and the technical aspects of major alternatives for building a new harbour area and managing the contaminated sediments. Considered uses of contaminated sediments are expected to be material for building harbour areas, disposal at sea and disposal on land (non-qualified use). The goal of the work package is to provide decision support especially to harbour companies so as to make the permit application process easier.
Keywords: stabilisation, solidification, contaminants, harbour.