Korrelation mellan hållfasthet i kalkcementpelare och oförstärkt lera : En studie av sonderingar utförda på projekt BanaVäg i Väst
A today common soil reinforcement method is the installation of lime-cement columns. Lime-cement columns have been used since the 1970’s and have been a useful method for stabilizing soil at great depths. It is mostly used for stabilizing road and railway embankments because the method is economically viable and the columns are easy to install. The total costs for the installation of the lime-cement columns is dependent on the numbers of installed columns, what percentage of lime and cement that has been used and the pattern in which the columns has been installed. It has been found that the method is more preferred from an environmental perspective than other stabilizing methods from a transport and pollution point of view.
A problem with the installation of lime-cement columns is that the stability of the columns has been varying, and that has contributed to costly quality controls. In many cases has a higher security factor than necessary been used, leading to more costs.
In this master thesis it has been evaluated whether is exists a relationship between the soils initial undrained shear strength and the evaluated shear strength of the lime-cement column reinforced soil. If such a relationship can be proved, the initial test of the soil might contribute to an easier estimation of how the strength in the columns will develop. It might also contribute to simplify the estimated quantity of the binder and facilitate the estimation of where the tests will be executed.
By using different probing and samplings results, the undrained shear strength and other parameters have been evaluated in about 50 sampling points. These have been compared to the shear strength in about 150 lime-cement columns along the new E45 between the cities Bohus and Nödinge in the south of Sweden. The area has been divided into 5 parts to see differences in the geographical areas. The lime-cement columns have been tested after 2 weeks and after 4 weeks after the installation to see the changes due to time. An analysis of how the shear strength in the columns is dependent of the shear strength in the soil along with the depth has been made.
The result indicates that the properties of the soil don’t vary significantly along the area, meaning that the differences in the results are dependent on the installation methods of the lime-cement columns and not by the changes in the soil.
It can be concluded that the shear strength in the soil increases by the depth, which is a result of the increasing
in-situ stress along with the depth. When analyzing the columns tested after 2 weeks it can be stated that there are no significant change of the shear strength along with the depth due to the increasing in-situ stress, and a week relationship could be seen when the columns had been tested after 4 weeks. The reason for this might be the impact of the hydration process meaning that the in-situ stress has a higher impact on the lime-cement columns by time.
The variation of the shear strength in the lime-cement in columns with the depth along the distance is independent of the shear strength in the soil, as can be seen from the determination coefficient in the studied intervals that didn’t exceed 10 % with reservation for a few misleading results. The geographical placement has a negligible impact on the lime-cement column-complex.
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