Management of Excavated Sulfide soils: Enhancing Mechanical Stability and Maintaining Moisture Content

Most scientific literature on sulfide-rich soils address the environmental hazard caused by the oxidation of Potential Acid Sulfate Soil (PASS) in its unoxidized form to Acid Sulfate Soil (ASS) when exposed to oxygen. Sulfide-rich soils pose also significant geotechnical challenges due to high water content and organic content, fine particles, lack of consolidation and acid-generating potential. Excavation and disposal are often necessary for infrastructure projects in e.g. Sweden and Finland. This thesis investigates approaches managing excavated sulfide soils by enhancing their mechanical properties for geotechnical applications and optimizing water content in the soil to mitigate oxidation risks. The research comprises three interrelated components. The first focuses on field experiments evaluating the efficiency of in-situ mixing techniques in improving the uniformity and mechanical stability of sulfide soil-binder mixtures. Results indicate that multi-stage mixing substantially enhanced soil-binder homogeneity and strength of the stabilized soil. Mechanical stability of laboratory prepared samples consistently outperformed those mixed in the field. A predictive model was developed to explain the observed trends, highlighting the critical roles of binder dosage, porosity, and water content in achieving stabilization. The second component examines the stabilization of acid sulfate soils using Portland cement and Multicem binders. Portland cement was more effective in enhancing mechanical properties due to its rapid increase in alkalinity, particularly in highly acidic soils. Multicem, while effective under moderately acidic conditions, was less successful in environments with high acidity. The study emphasized the importance of understanding the interactions between binder type, soil composition, and environmental factors. The final part investigates the role of multi-layer soil cover systems in mine and sulfide soil landfill designs in controlling moisture dynamics. Sulfide soil landfills were analyzed using numerical modeling validated through field instrumentation. The findings demonstrated that cover material properties, thickness, and the inclusion of features like capillary breaks are significant in maintaining moisture and minimizing environmental risks by oxidation. These insights were also applies to mine covers. This thesis provides a framework for a more sustainable management of sulfiderich soils by integrating findings from field experiments, laboratory, and numerical modeling. This study aims to contribute to the development of practical strategies to reduce society’s reliance on landfills for managing excavated sulfide soils, promoting geotechnical applications while mitigating environmental impacts.