Optimization of Laboratory Molding Techniques for Nordic Dry Deep Mixing

The dry deep mixing method is a widely used stabilization method in the Nordic countries to improve the strength and deformation properties of soft clays. In engineering practice, laboratory tests normally precede in situ stabilization; however, previous studies have shown considerable differences between field and laboratory stabilization. The type of laboratory molding technique will determine how representative the specimen is compared with field conditions. A key property is the amount of entrapped air in the stabilized clay, which is shown to be very low in field stabilization. This paper presents a study of two different Norwegian molding techniques, including different optimizations to reduce the amount of entrapped air. The specimens are tested for density and strength, and it is shown that the strength increases with increasing density of the stabilized clay. Consequently, there is an inverse relationship between the amount of entrapped air and the strength, showing the importance of reducing the amount of entrapped air in laboratory specimens as much as possible. It is also shown that the wet mixing method does not necessarily give the same strength development as dry deep mixing given the same water to binder ratio.