Abstract
When column stabilisation is meant to function as a ground improvement under an embankment, the design cases to be considered consist of overall stability, compression resistance of the column heads, arching of the embankment on the columns and settlements. This paper focuses on the compression resistance of the columns. The proper geotechnical design of deep mixed (deep stabilised) columns under road embankment requires good estimation of the stress-strain behaviour of the columns and the surrounding soil under the embankment and traffic loading. Earlier Finnish design approaches relied on an even traffic load of 10 kN/m2 on the road surface. The dimensioning methods for column stabilised soil are also based on the idea of an even traffic load. Due to Eurocode recommendations a more realistic scenario is introduced, which remarkably increases the magnitude of the traffic loading. After deriving suitable material properties and stiffness parameters for static and dynamic traffic loading, three-dimensional finite element calculations are performed to achieve better understanding of the mechanical interaction between the embankment, columns and soil under the new loading configuration. Even though more investigations are needed before delivering a final statement, the calculations show that, for the considered case in this paper, the new loading scenario has no relevant consequences on the design compared to the earlier design approach.
Highlights
Deep mixing or deep stabilisation is a widely used ground improvement method in Finland in areas of soft clay [10]
The implementation of the Eurocode approach with new traffic loads was the main drive behind updating the earlier guidelines from 2010 [9]
The loads presented in āGeotechnical Design, Application guidelines for Eurocode in Finnish Finnish Transport Agency (FTA)ās guideline NCCI7ā [8] are based on the measurements made on the Finnish road network during 2013 and 2014 [29]
Summary
Deep mixing or deep stabilisation is a widely used ground improvement method in Finland in areas of soft clay [10]. A mixing head is pushed and rotated though the soft subsoil into the desired depth. It is raised up by rotating while simultaneously adding binder material pneumatically into the soil [5]. According to the new regulations the traffic load became an evenly distributed load of 9 kN/m2 with an additional distributed load of 31 kN/m2 at the area of 3 m x 5 m on one lane. The location of this additional load can vary (Figure 1)
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