A field study of the mixing process of lime-cement columns for deep mixing has been carried out at a test site in Håby, Sweden. The study aimed to investigate the influence on the stabilisation effect and the coefficient of variation for excavated columns, when a number of factors related to the installation process were varied. The influencing factors investigated were the retrieval rate, number of mixing blades, rotational speed, air pressure in the storage tank, and diameter of the binder outlet hole. A large number of hand-operated penetrometer tests were carried out on the excavated column cross-sections. Statistical multifactor analyses were used to evaluate the influence on the stabilisation effect and the coefficient of variation of the varied factors. The results showed that the retrieval rate and the number of mixing blades were found to have a significant effect. The effect of rotational speed and the diameter of the outlet hole were found to be insignificant. The field study showed that the strength and deformation properties of the soil and the upper pair of mixing blades, with respect to the binder outlet hole, had a major influence on the binder dispersion over the column cross-section. The blade rotation number can be used as an indirect value of the mixing work and can be used as a measure of the mixing tool effectiveness.

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This paper presents results from work concerning development of the installation technique of lime-cement columns for ground improvement by deep mixing, as a part of the work of the Swedish Deep Stabilization Research Centre. A second field test was performed in order to test the findings from a previous work published by Larsson et al. The same methodology was adopted as in the previous work. However, the experimental programme was somewhat modified. Statistical analysis of variances, ANOVA, was used to investigate the influence of a number of factors in the mixing process: retrieval rate; number of mixing blades; rotation speed; air pressure in the binder tank; and diameter of the binder outlet hole. The analysis was performed with respect to the stabilisation effect and the coefficient of variation evaluated from hand-operated penetrometer tests on excavated column sections in open test pits. The retrieval rate and the number of mixing blades were found to have a significant effect. The effect of rotation speed, the binder tank air pressure, and the diameter of the outlet hole were insignificant. The two field studies illustrate the importance of performing a sufficient number of tests when studying influencing factors, because the strength is highly stochastic with large variations. Cet exposé présente les résultats de travaux concernant le développement de l'installation technique de colonnes de chaux-ciment pour améliorer le sol par mixage profond, dans le cadre des travaux du Centre de recherche sur la stabilisation profonde en Suède. Nous avons réalisé un second essai sur le terrain afin de tester les résultats d'une é tude précédente publiée par Larsson et al. Nous avons adopté la même méthodologie que dans les travaux précédents. Cependant, nous avons quelque peu modifié le programme expérimental. L'analyse statistique des variantes, ANOVA, a é té utilisée pour enquêter sur l'influence d'un certain nombre de facteurs dans le processus de mixage: taux de récupération, nombre de lames de mixage, vitesse de rotation, pression de l'air dans le réservoir d'agent liant et diamètre du trou de sortie de l'agent liant. L'analyse a é té faite relativement à l'effet de stabilisation et au coefficient de variation é valués à partir d'essais au pénétromètre manuel sur des sections de colonnes excavées dans des fosses d'essai ouvertes. Nous avons trouvé que le taux de récupération et le nombre de lames de mixage avaient un effet significatif. La vitesse de rotation, la pression d'air dans le réservoir de l'agent liant et le diamètre du trou de sortie n'avaient pas d'effet. Les deux é tudes sur le terrain montrent combien il est important de réaliser un nombre suffisant d'essais pour l'étude des facteurs influents, car la résistance est hautement stochastique avec de grandes variations.

A highway between Stockholm and Nynäshamn in Sweden was constructed in a geologically sensitive area with large deposits of highly compressible clay and organic soils overlaying large deposits of silt and sand resting on bedrock. A mixed ground improvement solution, using Vibro Replacement and Dry Soil Mixing for a 7-10 m high embankment, was designed and executed. The alternative design provided both technical and production advantages to the project. This paper presents the design and execution tasks that arose during the project due to the mixing of the two different ground improvement techniques. The used design method is presented together with the monitoring results of settlements as well as the results from field tests and field trials.

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