GeoCorner

The use of recycled materials can promote material efficiency and reduce the consumption of virgin aggregates. Recycled materials used in infrastructure construction have been extensively studied over the last 30-40 years. However, the reuse of excavated street structure layers has been very limitedly studied in Finland. In addition, there are no guidelines on this topic in Finland, and very little written material has been produced. This master's thesis examines the reuse of excavated soil materials from street structures in the base and sub-base layers of streets. The City of Helsinki commissioned this thesis.

Due to the lack of written material of studied topic, the literature review was supplemented with expert interviews. Based on the themes that required further investigation from the literature review, an interview study was conducted with clients and contractors in the infrastructure construction sector. The interview study was carried out as a semi-structured thematic interview. Based on the interview study, the reuse of soil materials in the base and sub-base layers of streets is small-scale in Finland. According to the interviews, providing guidelines for reuse of excavated soil material and improving the availability of interim storage and processing areas would promote the reuse of soil materials in structural layers.

The aim of the laboratory studies was to determine the quality of excavated soil materials and their technical properties used in the base and sub-base layers of streets in Helsinki. The laboratory tests studied the frost susceptibility of the soil samples by determining the gradation of the aggregates. Soil samples were taken from the current base and sub-base layers of four different sites in the Helsinki area. The quality of the soil samples varied, and a significant portion of the samples were frost-susceptible. Additionally, some of the soil samples contained various waste materials and organic material .

Based on the interview and laboratory studies, a significant challenge in recycling excavated soil materials is the poor and variable quality of the materials. Therefore, planning and comprehensive ground investigations are emphasized during the planning phase.