Strength variability in lime-cement columns based on cone penetration test data

Natural and improved soils have relatively high inherent property variability that should be taken into consideration in design. Investigations of the spatial variability in lime-cement columns are important since they provide a rational quantification of the variability parameters needed for a reliability-based design analysis of geotechnical systems. Statistical analyses are used to evaluate the spatial variability parameters, namely the mean, the variance and the scale of fluctuation, which is the distance within which soil properties reveal strong correlation. This paper presents a field test, in which 30 cone penetration test soundings were performed and analysed statistically in order to address the spatial variability in a group of lime-cement columns, with respect to the cone tip resistance. The objective of this paper is to describe the statistical analyses and to make a contribution to the empirical knowledge about strength variability in a volume of lime-cement columns. Stationarity has been assessed, and the scale of fluctuation has been evaluated in the vertical and horizontal directions. Random field theory was used based on the sample autocorrelation function. The scale of fluctuation was found to be within the range of 0·2–0·7 m and 2–3 m in the vertical and horizontal directions, respectively. A simple design consideration shows that the variance reduction factor has a major influence on the determination of the design value.