Characterization of strength variability for reliability-based design of lime-cement columns

Sincere thanks are directed to the Development Fund of the Swedish Construction Industry (SBUF) and to the Swedish Transport Administration (Trafikverket), whose financial support made this work possible. I would also like to thank my supervisor, Stefan Larsson, who has supported this work with his knowledge and never-ending enthusiasm. Further acknowledgments are directed to my colleagues at the Division of Soil and Rock Mechanics. Finally, I would like to thank my family – my wife, Helena, for her support and understanding, my daughter, Greta, for the joy she brings me and my parents, Sture and Ann-Charlotte, for their assistance. Without you, this work would never have been possible. Summary An expanding population and increased need for infrastructure increasingly necessitate construction on surfaces with poor soil conditions. To facilitate the construction of buildings, roads and railroads in areas with poor soil conditions, these areas are often improved by means of foundation engineering. Constructions that are fairly limited in scope are often founded on shallow or deep foundations. However, these methods are relatively expensive and thus not applicable for large-scale constructions like roads and railroads. A cost-effective way to deal with poor soil conditions is to use ground improvement. This thesis deals with a ground improvement method called deep mixing (í µí°·í µí±€) using lime-cement columns. Lime-cement columns are manufactured by pushing a mechanical mixing tool to the desired depth, with the tool then rotated and retracted while a lime-cement binder is distributed into soil, forming lime-cement columns. Because of the complex mixing process and inherent soil variability, soil improved by í µí°·í µí±€ shows high variability with respect to strength and deformation properties. Due to this high variability, it is difficult to predict the properties in advance; hence it is important to verify the properties after installation. In Sweden, this is normally done using the column penetration test (í µí°¾í µí±ƒí µí±†) method. Current design praxis considers evaluated mean values in the design, and the effect of variability and uncertainties is dealt with by using a sufficiently high total factor of safety. A more rational approach for dealing with the effect of variability and uncertainties on the reliability of a mechanical system is to include them as parameters in the design model. This can be done by using reliability-based design (í µí±…í µí°µí µí°·). A major incentive for using í µí±…í µí°µí µí°· is that lower variability in design properties produces …