Nearshore test field of wet deep soil mixing in Sweden

As a part of creating new living zones by using abandoned industrial areas in Stockholm, new residential areas will be built both on land and at sea. Due to the difficult soil conditions under the seabed, where silt and soft clay are present, a design is being developed with soil improvement to ensure the stability of the natural soil and the embankment of reclamation fill. Cement columns are pre-designed to improve weak soil layers ranging from 10 meters to approximately 25 meters in depth, underlain by moraine layers, while the water depth is approximately 10 meters. The decision on how to construct the cement columns will be taken and the design will be finalized based on the results of the test field. While dry deep soil mixing is the predominant and widely accepted soil improvement method in Sweden, the test field was carried out using wet deep soil mixing (wet DSM). Nonetheless, prior laboratory investigations involved both dry and wet soil mixing techniques. In the project, 37 columns with a diameter of 2.4 meters were constructed using a 130-tonne rig standing on the barge under challenging weather conditions and the dynamic impacts of the sea. Cement and cement/slag (30/70) were used as binders at different dosages. Column verticality was controlled during installation using a verticality sensor mounted on the mixing tool. Wet grab and core sampling was carried out to inspect the quality of mixing along the columns and within the clay/moraine transition zone. This project is known as the first wet DSM application in Sweden, proving the future of this technique in Scandinavia.