Utvärdering av stabiliseringsmetoder för sulfidhaltig jord i norra Sverige och kemiska parametrars påverkan

Sammanfattning

The report explores the stabilization of sulfide soil using lime-cement columns (LC columns) and mass stabilization, two common methods used to improve the bearing capacity and stability of soil. Sulfide soil is a problematic soil type that, when exposed to oxygen, undergoes chemical reactions that can lead to acidification and the release of metals and other harmful substances to the environment and building material can corrode, making it difficult to handle when exposed to oxygen. Additionally, sulfide soil is complex to stabilize due to its high content of fine-grained material and chemically composing. These processes pose challenges for construction and the environment, especially in areas where sulfide soil is encountered, where it either needs to be deposited or stabilized without exposed to oxygen. Previous research has addressed this issue, but there is lack of information about which chemical parameters should be examined and their impact on stabilization. By investigating these aspects, both costs and environmental impact can be reduced. The aim of this study is to investigate and analyze which chemical parameters affect the stabilization of sulfide soil and how to best optimize the stabilization process by combining different percentages of lime and cement with various mixing ratios. It is known from previous research that sulfide soil can vary in its stabilization capacity depending on its chemical composition, particularly the levels of sulfur, iron, and calcium, as well as the pH value. Through previously conducted laboratory analyses and a literature review, data was collected from an ongoing project on Tyréns project of the Norrbotniabanan railway, where sulfide soil was identified through geotechnical surveys. Soil samples were taken from five different locations along the route, including different depths, and were then mixed with predetermined binders and mixing ratios in a geotechnical laboratory to examine their effect on shear strength and curing rate. The results showed that different chemical parameters have varying impacts on the stabilization process. Sulfur content was found to have a negative effect on shear strength in the early stages of curing, but over time, higher sulfur content contributed to better strength. Similarly, calcium and iron had different effects depending on the soil's depth and composition. In general, shear strength increased over time and with higher concentrations of binders, which were compared against the critical shear strength required for the project. However, a few samples did not follow the trends and were difficult to analyze. The study identifies that a deeper understanding of the chemical parameters in sulfide soil is important to achieve effective stabilization. By optimizing the choice of binders and adapting them to the specific conditions of each project, stabilization can be improved. This can lead to safer constructions and reduced over-dimensioning of stabilization, ultimately decreasing the environmental impact. The work provides important insight into how the industry still needs to develop and conduct further research to understand why sulfide soil is a complex soil type to stabilize and what factors influence its stabilization potential.