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Effect of spatial variability of the strength properties in lime-cement columns on embankment stability
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0001-9615-4861
2012 (English)In: Geotechnical Special Publication, ISSN 0895-0563, Vol. 228, 231-242 p.Article in journal (Refereed) Published
Abstract [en]

Spatial variability with respect to the strength in lime-cement columns is an unavoidable source of uncertainty that should be considered in design. Current design method for the assessment of embankment stability, based on the deterministic factor of safety, cannot address the effect of spatial variability. Reliability-based design methodology is a powerful tool that can be used to integrate the variability into the analysis. In this paper, the spatial variability with respect to the undrained shear strength in the soil and in the columns was evaluated based on CPT test. The first order second moment (FOSM) reliability method was applied to address the impact of the spatial variability of the strength in the soil and in the columns on the reliability of an embankment founded on improved soil by lime-cement columns. The paper also presents a technique to evaluate the variance reduction factor over the failure surface. The results propose that the undrained shear strength in the soil and in the columns can be modelled following normal or lognormal distribution. The analysed example show that the reliability increased significantly when the spatial variability was considered

Place, publisher, year, edition, pages
2012. Vol. 228, 231-242 p.
National Category
Civil Engineering Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-59082DOI: 10.1061/9780784412350.0009Scopus ID: 2-s2.0-84888341110OAI: oai:DiVA.org:kth-59082DiVA: diva2:474981
Conference
International Conference on Grouting and Deep Mixing
Note

QC 20150629

Available from: 2012-01-10 Created: 2012-01-10 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Strength variability in lime-cement columns and its effect on the reliability of embankments
Open this publication in new window or tab >>Strength variability in lime-cement columns and its effect on the reliability of embankments
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Ground improvement by deep mixing (DM) is a generic term used for a number of methods in which a binding agent, often lime and/or cement, is mechanically mixed with the soil to increase its engineering properties. The inherent variability with respect to the engineering properties of the improved soil is high due to the variations in geology and the complex mixing process. High variability introduces uncertainty in estimating improved soil properties and the performance of the structure.

Current design methodology deals with soil properties deterministically and the uncertainties involved are incorporated in a single value represented by a total factor of safety (FS). The chosen FS is highly dependent on the engineer’s judgment and past experience, in which both of these factors vary between different geotechnical designers. Therefore, current design methodology used in practice for DM does not deal with uncertainties in a rational way. In order to design a geotechnical system with the desired level of confidence, the uncertainties involved must be integrated in the DM design. This can be achieved by using reliability-based design (RBD) methods.

The research work in this thesis is presented as a collection of three papers. In the first paper, a comprehensive statistical analysis of cone penetration test (CPT) data is described. The objective was to make a contribution to empirical knowledge by evaluating the strength variability of lime-cement columns within the group of tested columns. In the second paper, the effect of the spatial variability and statistical uncertainty with regard to the embankment’s reliability was investigated within the framework of RBD. The study in the third paper investigated the strength variability in lime-cement columns based on two test methods, namely CPT and column penetration test (KPS). In this study, the effect of different test methods on the evaluation of the design value was addressed.

The main conclusions from this study can be summarized as follows. First, the probability distribution function (PDF) for the undrained shear strength of lime-cement columns can be modeled in RBD as normal or log-normal distributions. However, the use of log-normal distribution is recommended for RBD analyses. Second, the evaluated scales of fluctuation indicate ranges of 2 to 4 m and 0.2 to 0.8 m in the horizontal and the vertical directions respectively. This means that in order to fulfill the requirements of independent/uncorrelated samples for assessment of the design value, the spacing between samples must exceed the horizontal scale of fluctuation. It is therefore proposed that the spacing between individual samples should be at least 4 meters. Third, the design values evaluated using CPT and KPS were approximately the same. However, the inherent variability evaluated differs due to the larger volume tested with the KPS probe than with the CPT probe. However, this difference was not significant between the two tests. Fourthly, due to the limitation in the deterministic design in terms of dealing with uncertainties, it is recommended that RBD design should be used in parallel with the deterministic design of lime-cement column.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. v, 35 p.
Series
TRITA-JOB. LIC, ISSN 1650-951X ; 2016
Keyword
lime-cement, embankments
National Category
Civil Engineering Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-57992 (URN)
Presentation
2012-02-06, Q2, Osquldasväg 10 NB, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20120110

Available from: 2012-01-10 Created: 2012-01-04 Last updated: 2014-06-18Bibliographically approved

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Larsson, Stefan

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