This report presents a research project on the long-term properties of lime-cement columns that were installed in clay at three field sites approximately 20–30 years ago in connection with infrastructure projects on the Swedish west coast. The purpose of the research project was to investigate homogeneity and strength through predrilled column penetration test (pillar sounding) and sampling of the columns in the field, as well as laboratory testing. A further aim was to develop laboratory equipment and methodology for leaching tests for accelerated ageing, and to carry out leaching tests on core samples from the columns. In the field, sampling in the columns was carried out with S-Geobor, and in the laboratory the strength of the core samples was examined through uniaxial compression tests and shear punching tests. The homogeneity of the columns was investigated through visual inspection and X-ray tomography of the core samples.
The results of the investigations show that the lime-cement columns have significantly higher strength after 30 years than what was assumed in the design of the reinforcement measure. The strength of the lime-cement columns has increased somewhat compared with the strength measured in pillar soundings performed after about 10 years.
The strength evaluated from the pillar soundings in the field does not correspond with the strength evaluated from the laboratory tests. The laboratory tests generally show a large variation in strength at roughly the same levels, both between different columns and within a single column.
The probing results from the pillar soundings generally show a greater variation in evaluated strength between the columns at each site in the upper two meters than at greater depths. Based on visual assessment of the core samples from the columns, there were larger variations in the mixing of the binder with the clay in the upper two meters than below. The variation in strength between columns, as well as the difference in strength with depth, has been statistically quantified for the pillar soundings at the Håby field site.
During pillar sounding, the vane can deviate from the column and gradually transition from measuring probing resistance (strength) in the column to that in the surrounding natural soil. This should be considered when analysing results from column probing. The use of S-Geobor for obtaining core samples from the lime-cement columns in the field worked well. The samples were generally of high quality.
A modified apparatus has been developed to perform accelerated leaching tests in the laboratory on samples taken from stabilized columns in the field.