Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Aspects of probabalistic serviceability limit state design of dry deep mixing
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

An expanding population and increased need for infrastructure increasingly necessitate construction on surfaces with poor soil conditions. To facilitate the construction of buildings, roads and railroads in areas with poor soil conditions, these areas are often improved by means of foundation engineering. Constructions that are fairly limited in scope are often founded on shallow or deep foundations. However, these methods are relatively expensive and thus not applicable for large-scale constructions like roads and railroads. A cost-effective way to deal with poor soil conditions is to use ground improvement. This thesis deals with a ground improvement method called deep mixing (DD)using lime-cement columns.

Lime-cement columns are manufactured by pushing a mechanical mixing tool to the desired depth, with the tool then rotated and retracted while a lime-cement binder is distributed into soil, forming lime-cement columns. Because of the complex mixing process and inherent soil variability, soil improved by DD shows high variability with respect to strength and deformation properties. Due to this high variability, it is difficult to predict the properties in advance; it is therefore important to verify the properties after installation. In Sweden, this is normally done using the column penetration test (KKK) method.

Current design praxis considers evaluated mean values in the design, and the effect of variability and uncertainties is dealt with by using a sufficiently high total factor of safety. A more rational approach for dealing with the effect of variability and uncertainties on the reliability of a mechanical system is to include them as parameters in the design model. This can be done by using reliability-based design (RRR). A major incentive for using đť‘…đť‘…đť‘… is that lower variability in design properties produces higher design values. This is important since it encourages contractors to improve their manufacturing methodologies because đť‘…đť‘…đť‘… allows more homogenous columns to be assigned higher design values. Reliability-based design is also in line with Eurocode 7, which states that the selection of the characteristic values for geotechnical parameters shall take the variability of the measured property values into account.

The first part of this doctoral thesis deals with test methods and quantification of the strength variability of soil improved by lime-cement columns. Tip resistances from three different test sites using three different penetration test methods – the cone penetration test, the column penetration test and the total-sounding test – are analysed and quantified in terms of means, variances and scale of fluctuations. The second part introduces RRR in serviceability limit state (SSS) design, using First Order Reliability Methods (FFFF) and Monte-Carlo simulations.

Summarizing the most important findings and conclusions from this study:

  •  The scale of fluctuation was estimated to be 0.2-0.7 m and 0-3 m in the vertical and horizontal direction, respectively.
  •  The relation between cone tip resistances measured using the cone penetration test and column penetration test does not correspond to the cone factors proposed in previous studies and in the Swedish Design Guidelines.
  •  The agreement between the column penetration test and total-sounding test was found to be “good enough”. It is therefore suggested that the total-sounding test be used as a complement to the column penetration test in evaluating the average strength properties of a group of medium- and high-strength lime-cement columns.
  • Reliability-based design is a rational approach to incorporate strength and deformation parameter variability with an SSS design.
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xii, 48 p.
Series
TRITA-JOB PHD, ISSN 1650-9501 ; 1019
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-168596OAI: oai:DiVA.org:kth-168596DiVA: diva2:817375
Public defence
2015-06-10, Sal B1, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150605

Available from: 2015-06-05 Created: 2015-06-05 Last updated: 2016-07-05Bibliographically approved
List of papers
1. Strength variability in lime-cement columns based on CPT data
Open this publication in new window or tab >>Strength variability in lime-cement columns based on CPT data
2012 (English)In: Ground Improvement, ISSN 1365-781X, E-ISSN 1751-7621, Vol. 165, no 1, 15--30 p.Article in journal (Refereed) Published
Abstract [en]

Natural and improved soils have relatively high inherent property variability that should be taken into consideration in design. Investigations of the spatial variability in lime-cement columns are important since they provide a rational quantification of the variability parameters needed for a reliability-based design analysis of geotechnical systems. Statistical analyses are used to evaluate the spatial variability parameters, i.e. the mean, the variance, and the scale of fluctuation, which is the distance within which soil properties reveal strong correlation. This paper presents a field test, in which 30 CPT soundings were performed and analyzed statistically in order to address the spatial variability in a group of lime-cement columns, with respect to the cone tip resistance. The objective of this paper is to describe the statistical analyses and to make a contribution to the empirical knowledge about strength variability in a volume of lime-cement columns. Stationarity has been assessed, and the scale of fluctuation has been evaluated in the vertical and horizontal directions. Random field theory was used based on the sample autocorrelation function ACF. The scale of fluctuation was found to be within the range of 0.2-0.7 m and 2-3 m in the vertical and horizontal direction, respectively. A simple design consideration shows that the variance reduction factor has a major influence on the determination of the design value.

Keyword
ground improvement, deep mixing, lime-cement columns, statistical analyses, spatial variability, cone penetration test
National Category
Civil Engineering Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-59086 (URN)10.1680/grim.2012.165.1.15 (DOI)2-s2.0-84858857990 (Scopus ID)
Note

QC 20150622

Available from: 2012-01-10 Created: 2012-01-10 Last updated: 2017-12-08Bibliographically approved
2. Variability of strength and deformation properties in lime-cement columns evaluated from CPT and KPS measurements
Open this publication in new window or tab >>Variability of strength and deformation properties in lime-cement columns evaluated from CPT and KPS measurements
2013 (English)In: Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, ISSN 1749-9518, E-ISSN 1749-9526, Vol. 7, no 1, 21-36 p.Article in journal (Refereed) Published
Abstract [en]

The strength variability of soil improved by deep mixing with lime-cement columns is generally high. Eurocode 7 states that selection of characteristic values for geotechnical parameters shall take the variability of measured property values into account. This variability can be considered in the design by using reliability-based design. With reliability-based design, three statistical parameters are needed to evaluate the design value; mean, variance and scale of fluctuation. In this paper, the shear strength of soil improved by lime-cement columns was evaluated using two different penetration methods, the cone penetration test and the column penetration test. The strength was quantified statistically by the mean, variance and scale of fluctuation, while each test method was analyzed and discussed with a focus on its influence on the design value. Based on the analyses, the column penetration test is suggested as a test method for soil improved by lime-cement columns.

Keyword
ground improvement, deep mixing, lime-cement columns, CPT, column penetration test
National Category
Civil Engineering Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-59088 (URN)10.1080/17499518.2013.763571 (DOI)2-s2.0-84874191684 (Scopus ID)
Note

QC 20140618. Tidigare titel: "Strength variability in lime-cement columns evaluated using CPT and KPS"

Available from: 2012-01-10 Created: 2012-01-10 Last updated: 2017-12-08Bibliographically approved
3. Comparing column penetration and total–sounding data for lime–cement columns
Open this publication in new window or tab >>Comparing column penetration and total–sounding data for lime–cement columns
2014 (English)In: Ground Improvement, ISSN 1365-781X, E-ISSN 1751-7621, Vol. 167, no 4, 249-259 p.Article in journal (Refereed) Published
Abstract [en]

In Sweden, the method commonly used for the quality control of lime–cement columns is the column penetration test. However, it is recommended for depths of no more than 8 m because the probe easily deviates from the column at greater depths. As an alternative to facilitate keeping the probe vertical, a centre hole is normally bored in the column using the total-sounding test method. The aim of this paper is to quantify the agreement between the two methods. If there is good agreement, it should be possible to use the less expensive and less time-consuming total-sounding test as a complement to the column penetration test. The analyses suggest good agreement between the methods, and it is therefore suggested that the total-sounding test be used as a complement to the column penetration test in evaluating the average strength properties of a group of medium- and high-strength lime–cement columns.

Place, publisher, year, edition, pages
Thomas Telford, 2014
Keyword
ground improvement, deep mixing, correlation, agreement, column penetration test, total-sounding test, rotary penetration test
National Category
Civil Engineering Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-98814 (URN)10.1680/grim.12.00019 (DOI)2-s2.0-84912092226 (Scopus ID)
Note

QC 20150622

Available from: 2012-07-03 Created: 2012-07-03 Last updated: 2017-12-07Bibliographically approved
4. Serviceability Limit State design of lime-cement columns - A reliability-based design approach
Open this publication in new window or tab >>Serviceability Limit State design of lime-cement columns - A reliability-based design approach
2014 (English)In: Geotechnical Safety and Risk IV - Proceedings of the 4th International Symposium on Geotechnical Safety and Risk, ISGSR 2013 / [ed] D . Q . Li, London: Taylor & Francis Group, 2014, 417-422 p.Conference paper, Published paper (Refereed)
Abstract [en]

Deep mixing with lime-cement columns is a ground improvement method used to improve the strength and deformation properties of soft cohesive soils. Due to the complex manufacturing process, the variability in the strength and deformation properties is normally high. A rational approach to include variability in the design process is by introducing Reliability-Based Design (RBD). This paper presents a reliability-based design approach for Serviceability Limit State (SLS) design of soil improved by lime-cement columns using the First-Order Reliability Method (FORM). The paper further presents the impact of uncertainties, reliability indices and area replacement ratios on the relationship between the characteristic value and the design value with respect to the column modulus of elasticity.

Place, publisher, year, edition, pages
London: Taylor & Francis Group, 2014
Keyword
Deformation, Lime, Reliability, Safety engineering, Soil cement, Strength of materials
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-144473 (URN)10.1201/b16058-64 (DOI)2-s2.0-84896842327 (Scopus ID)978-1-138-00163-3 (ISBN)
Conference
4th International Symposium on Geotechnical Safety and Risk, ISGSR 2013; Hong Kong; Hong Kong; 4 December 2013 through 6 December 2013
Note

QC 20140520

Available from: 2014-04-23 Created: 2014-04-23 Last updated: 2015-06-05Bibliographically approved
5. Probabilistic design of dry deep mixing using an observational approach
Open this publication in new window or tab >>Probabilistic design of dry deep mixing using an observational approach
2015 (English)In: Ground Improvement, ISSN 1365-781X, E-ISSN 1751-7621, Vol. 168, no 4, 300-311 p.Article in journal (Refereed) Published
Abstract [en]

The evaluation of material parameters for design should consider the spatial variability of measured parameters, the extent and type of tests, and the type and size of the current mechanical system. This is stated in Eurocode 7; however, there is very little guidance as to how this is to be done in practice. The strength and deformation properties of dry deep mixing columns are subject to high variability, and it is difficult to estimate these parameters in advance. Owing to this high variability, probabilistic analyses are considered useful for the design and quality assessment decision procedure. This paper presents a procedure, based on probabilistic analysis, which is a combination of design by calculation and the observational method. The procedure renders the possibility to update acceptance criteria based on measurements during construction, and the methodology rewards the development of the mixing process and increased testing.

Place, publisher, year, edition, pages
ICE Publishing, 2015
Keyword
design methods & aids, quality control, statistical analysis
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-157737 (URN)10.1680/grim.14.00011 (DOI)000370554100006 ()
Note

QC 20150113. QC 20160318

Available from: 2014-12-13 Created: 2014-12-13 Last updated: 2017-12-05Bibliographically approved
6. Probabilistic serviceability limit statedesign approach for dry deep mixing
Open this publication in new window or tab >>Probabilistic serviceability limit statedesign approach for dry deep mixing
(English)Manuscript (preprint) (Other academic)
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-168591 (URN)
Note

QS 2015

Available from: 2015-06-05 Created: 2015-06-05 Last updated: 2015-06-05Bibliographically approved

Open Access in DiVA

Thesis(1435 kB)183 downloads
File information
File name FULLTEXT01.pdfFile size 1435 kBChecksum SHA-512
32f4a5f087458a245b084913c63753cb47cdbe6b3c755930ccdc4d25f18432144add0d63975799e0e38986eefd48182c93b8978ccdbac493f3af8d442567db38
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Bergman, Niclas
By organisation
Soil and Rock Mechanics
Geotechnical Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 183 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

urn-nbn

Altmetric score

urn-nbn
Total: 416 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf