Project activities
WP1:
Management of sulfidic soils under waterlogged (anaerobic) conditions and with different amendments
The objective of WP1 is to investigate if sulfate and metal immobilisation is achievable by waterlogging sulfidic soils with different degrees of oxidation (air exposure) and different amendments. Previous studies showed that stabilisation of sulfidic soil with limestone successfully neutralised the acid formed, as well as immobilising many of the metals although it was not possible to halt the leaching of sulfate and some metals. Further knowledge is needed to understand the geochemical and microbiological processes controlling sulfate mobilisation to ensure acidification mitigation measures applied to excavated sulfidic soil do not negatively affect groundwater and nearby water streams.
If sulfate and metal mobilisation cannot be avoided or minimised after sulfidic soil stabilisation, an ecological compensation act could be an alternative for practitioners involved in land development projects. This project will investigate waterlogging of sulfidic soils, with or without amendments, as a compensatory measure.
WP2:
Management of sulfidic soils under drained (aerobic) conditions and with different amendments
The objective of WP2 is to provide tools to practitioners involved in land development projects to guarantee an environmentally safe use of sulfidic soils on-site, where the oxidation and the leaching of sulfate and metals are controlled. Sulfidic soils are mainly excavated in connection with infrastructure projects and urban expansion due to poor geotechnical properties. Local solutions for soil management, e.g., use of sulfidic soil as a resource in constructions, are needed to reduce costly and polluting transports to landfills. In order to use the sulfidic soil as a resource in e.g., noise barriers, the soil needs to be amended or covered to minimise the negative environmental effects caused by sulfide oxidation.
A reliable prediction of the degree of water saturation in the soil (i.e., the amount of water in the pores) is needed to ensure a durable storage of the excavated soil. Partially saturated sulfidic soils storage constructions i.e., in situations where the base of the sulfidic soil is in contact with the water table, is volume efficient compared to underwater storage although part of the soil volume is exposed to drained conditions. The oxidation process in sulfidic soil is controlled by the degree of water saturation in the soil. A numerical model can be used to predict the water content in the soil depending on the climatic conditions at a specific site, the soil properties and the shape of the deposit. Such a tool would facilitate the design of local soil disposal facilities, limiting the need for transport.
WP3:
Management of sulfidic soils with cement amendment
The objective of WP3 is to provide dimensioning data used by constructors to determine a safety factor that enables construction with stabilised sulfidic soil, to test and guarantee the technical properties of stabilised soil based on laboratory experiments and to ensure environmentally safe use of excavated sulfidic soil in earth structures. WP3 will extend the knowledge gained in the STASIS project regarding cement-based soil stabilisation to a variety of sulfidic soils with the aim to better understand the variability of the stabilisation process.
Alteration of sulfidic soil in order to fulfil e.g., a specific strength requirement, will modify the soil texture and will affect the water transport through and leaching from the soil. In order to design a resource efficient and durable construction with stabilised sulfidic soil, there is a need to better understand and predict the field performance of the treated soil.
Results from previous work in the STASIS project showed a discrepancy between laboratory results and what was obtained in the field. A numerical model was established for one soil and one binder that can be used to predict strength of stabilised sulfidic soil under field conditions. In this project, a sensitivity analysis and a validation of this numerical model will be made to determine the factors that impact most the strength of the stabilised soil under other conditions, which will facilitate the design of sulfidic soil structures. It will further promote the valorisation of sulfidic soil as well as limit the environmental impact of sulfidic soil excavation and transport.
WP4:
Best practice development by bridging the gap between knowledge base and practice
Legislation regarding management of excavated sulfidic soil is complex and differs between the two countries and hence, can become an obstacle to valorisation of excavated soil. Therefore, there is a need to increase awareness and provide contractors and decision makers with strategies to address permit issues and ensure sustainable projects with a positive and durable environmental effect are not abandoned because of judicial issues.
The aim of WP4 is to build cross-border best practices regarding the handling of sulfidic soils that will be developed in the project’s cross-border network through a mutual transfer of knowledge between the project partners and the target group. The project partners will provide the knowledge needed, gathered in WPs 1-3, and the participants in the reference group will provide a practical orientation to ensure that the best practices will be tailored to the actual situation. This will bridge the gap between knowledge base and practice and help decision making by the authorities and the implementation of methods of safe soil use and/or disposal by other stakeholders involved in land development projects. Dåva DAC will review the Swedish and Finnish legislations regarding landfills and describe how to apply for a landfill permit in a Swedish context and how the Dåva Norra landfill has been constructed and how it is monitored. Novia coordinates WP4 but all partners are responsible for the content.
