Towards Sustainable Ground Improvement: a Life Cycle Assessment of Stone Columns and Dry Soil Mixing in Norwegian Clays

In Scandinavia, the most common used ground improvement method is dry soil mixing using typically lime and cement as the stabilizing binders which uses large amounts of cement and thus contributes to the global warming potential of construction projects - typically quantified in terms of carbon dioxide equivalents (CO2-eq). Vibro replacement is a widely adopted ground improvement method aiming to increase the stiffness and strength of the soil by installing stone columns. The research project VIBE funded by RFF Oslo and initiated by Keller and NGI investigates possibilities and limitations of the vibro replacement method in Norwegian clays. Primary and secondary (recycled) aggregates were used for the stone column installation at the full-scale test site Onsøy. This paper presents a comprehensive Life Cycle Assessment of the executed soil improvement work using the European Federation of Foundation Contractors (EFFC) carbon calculator and a modified approach using CO2-eq representative for Scandinavia. In the second step the calculated carbon footprint is compared to an alternative ground improvement method, namely dry soil mixing. Therefore, the CO2 emissions were estimated for a typical construction site by assuming an equivalent ground improvement stiffness. It is shown that vibro replacement leads to significantly smaller CO2 emissions compared to dry soil mixing if an adequate improvement factor is assumed. Emissions can further be decreased during the stone column installation when using secondary aggregates (instead of primary aggregates) and assuming no extensive processing of the material. The findings offer valuable insights in a more sustainable ground improvement, showing great potential for Scandinavian clays.