Trans-scale spatial variability of lime-cement mixed columns

Artikel i vetenskaplig tidskrift, 2024

Lime-cement columns are a common form of ground improvement used in the Nordic countries to improve the engineering properties of soft soils. The strength and stiffness of lime-cement mixed clay, however, are heterogeneous. Hence, the characterisation of the extent of variability of strength and stiffness is essential to optimise the performance of lime-cement columns. This paper presents an integrated approach to characterise the variability in strength and stiffness of samples from 1 year old lime-cement columns in natural sensitive clay, from the Centralen project site in Gothenburg, Sweden. A novel image-based method is proposed to characterise the spatial variability at the laboratory scale, using a stereoscopic digital image correlation (DIC) system in addition to X-ray Computed Tomography (XCT) scans. Data from column penetration tests (FKPS) and reverse column penetration tests (FOPS) on the lime-cement columns at the excavation site were used to estimate the spatial variability at the field scale. The key finding of this work is that different magnitudes of scales of fluctuations exist for the lime-cement mixed clay under laboratory scale and field scale testing. The results serve to highlight the ever-present problem of inherent variability in lime-cement mixed soils and challenges to accurately characterise this variability. Thus, further work is required to relate scale of fluctuation of strength to that of stiffness, and to link scale of fluctuation at laboratory scale with that at field scale.