Strength and Verticality of Nordic Dry Deep Mixing Columns—A Case Study in Norway

This paper presents a case study in Norway where dry deep mixing was used extensively in one project to improve soft clays in several areas spanning 19 km in distance. Using the same execution parameters, same binder content (50 kg/m3) and the same binder type (cement, quicklime and lime kiln dust) throughout the project, this enabled studies of how the strength development relates to different clay properties. Elevation-based linear correlation analyses and machine learning techniques showed that the strength development was not correlated with sensitivity but had a weak correlation with water content and consistency limits. The verticality of 30 deep mixing columns was also investigated using a high-accuracy gyroscope-inclination sensor. The results show that the construction error requirements were fulfilled down to around 5 m depth, where under large deviation occurs, mainly due to bending of the drilling rod. The largest deviation at 15 m depth was around 1.6 m. These construction errors call for a certain conservatism in design practice.