Strength and Stiffness Properties of Laboratory-Improved Soft Swedish Clays

The dry deep mixing method using lime and cement-based binders is widely used in the Nordic countries to improve soft and sensitive clays. Increasing the usage of industrial by-products is needed to reduce climate impact, and this requires thorough knowledge on engineering properties using these binders. A lot of research has been done on this topic; however, tests are often performed on fabricated soils, and there is also a lack of studies on cement kiln dust in organic clays. This paper presents a large database of laboratory-improved soft inorganic and organic natural Swedish clays using quicklime, cement and cement kiln dust. It is shown that many properties and relationships between strength and stiffness, strength development over time and strain to failure are in practice similar for both quicklime and cement kiln dust when combined with cement, but that the strength depends both on the water-binder ratio and soil type. Further, it is shown that cement kiln dust performs well also in organic clay. The data also shows that the Youngs' modulus on average is around 100 times the unconfined compressive strength. For strength development over time, it is seen that the strength increases on average 60% from 7 days of curing to 28 days of curing. The correlations presented herein will serve as a useful guidance in engineering practice.