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Embankments founded on sulphide clay: - some aspects related to ground improvement by vertical drains
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, some aspects concerning building embankments founded on sulphide clay are studied, with special reference to ground improvement by preloading in combination with prefabricated vertical drains (PVD’s). The main purpose of the research was to increase empirical knowledge of the mechanical behaviour of sulphide clays subjected to embankment loadings and of the interaction between vertical drains and sulphide clays. Important aspects related to ground improvement with PVD’s in more general terms are also treated, in particular how various uncertainties regarding the properties of the clay and the clay-drain interaction imposed in the design phase can be addressed. The benefits of using theobservational method for handling these uncertainties are discussed, and a description of how the method was used in an embankment project is presented. The results from the research are presented in one conference paper and two papers submitted to peer-reviewed international journals, which are appended.

The design of PVD’s involves describing the consolidation characteristics of the clay and the interaction between the drains and the clay. Primarily, the rate of consolidation is determined by the hydraulic conductivity (permeability) of the clay in the horizontal direction. Hence, accurate determination of this material property is of paramount importance in making reliable design predictions. As conventional laboratory tests for assessing the consolidation characteristics of a clay only provide information about its properties in the vertical direction, one is often left to make assumptions about the horizontal properties based on empirical correlations. Reliable empirical knowledge of these correlations for a certain clay is there forevital. A large number of CRS tests were performed on horizontal and vertical samples ofsulphide clay in order to investigate the correlation between the horizontal and verticalhydraulic conductivity and coefficient of consolidation. The results show that there is very small anisotropy in these parameters and that the scatters in the results are large. For designpurposes, sulphide clays should therefore be assumed to be isotropic in this respect. In orde rto handle the variation in properties, several parallel tests should be made and partial factors of safety should be introduced in the design. Introducing partial factors of safety in the design of PVD’s is one of the main topics suggested for further research. Regarding the clay-drain interaction, a study of the disturbance effects (smear effects) during the installation of drains in sulphide clays was performed. Back-calculations of measurements of pore pressure dissipation were made via a parameter study. It was shown that smear affects the consolidation rate to some extent but that the natural (undisturbed) hydraulic conductivity is more significant.

The undrained shear strength su of a clay is dependent on the preconsolidation pressure σ 'p . As the clay consolidates under a loading, the effective stress increases, possibly to magnitudes surpassing the initial preconsolidation pressure and thereby leading to increased undrainedshear strength of the clay. The relation between su and σ 'p, i.e. the ratio su /σ 'p for asulphide clay, was investigated based on results from a large number of in situ tests andlaboratory tests. There were large scatters in the measurements, but su /σ 'p =0.25 is suggested as being relevant in the direct shear zone for design purposes in sulphide clays.

Place, publisher, year, edition, pages
Stockhollm: KTH , 2010. , xiv, 48 p.
Series
TRITA-JOB. LIC, ISSN 1650-951X ; 2015
Keyword [en]
geotechnical engineering; embankments; vertical drains; sulphide clay
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-25802OAI: oai:DiVA.org:kth-25802DiVA: diva2:359899
Presentation
2010-10-11, E2, Lindstedtsvägen 3, KTH, Stockholm, 15:06
Opponent
Supervisors
Note

QC 20101101

Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2014-06-16Bibliographically approved
List of papers
1. Veda trial embankment-comparison between measured and calculated deformations and pore pressure development
Open this publication in new window or tab >>Veda trial embankment-comparison between measured and calculated deformations and pore pressure development
2009 (English)In: GEOTECHNICS OF SOFT SOILS - FOCUS ON GROUND IMPROVEMENT / [ed] Karstunen M, Leoni M, BOCA RATON: CRC PRESS-TAYLOR & FRANCIS GROUP , 2009, 405-410 p.Conference paper, Published paper (Refereed)
Abstract [en]

The Veda embankment is about 300 metres long, up to 16 metres high and is being built as a staged construction on vertically drained subsoil consisting of very loose post glacial sulphide clay and very loose glacial clay. The Veda trial embankment was built one year in advance in order to obtain essential knowledge about the behaviour of the subsoil when subjected to an embankment load. This paper present and discuss the process of using the measurements from the trial embankment together with laboratory tests in order to establish a numerical analysis for the Veda embankment, that describes the behaviour of the soil sufficiently well as a foundation for the design and prediction according to the observational method.

Place, publisher, year, edition, pages
BOCA RATON: CRC PRESS-TAYLOR & FRANCIS GROUP, 2009
National Category
Mineral and Mine Engineering
Identifiers
urn:nbn:se:kth:diva-30826 (URN)000267057000053 ()2-s2.0-79952358110 (Scopus ID)978-0-415-47591-4 (ISBN)
Conference
2nd International Workshop on Geotechnics of Soft Soils Glasgow, SCOTLAND, SEP 03-05, 2008
Note
QC 20110310Available from: 2011-03-10 Created: 2011-03-04 Last updated: 2014-06-16Bibliographically approved
2. Hydraulic Conductivity and Coefficient of Consolidation of Two Sulphide Clays in Sweden
Open this publication in new window or tab >>Hydraulic Conductivity and Coefficient of Consolidation of Two Sulphide Clays in Sweden
2012 (English)In: Geotechnical and Geological Engineering, ISSN 0960-3182, E-ISSN 1573-1529, Vol. 30, no 1, 173-186 p.Article in journal (Refereed) Published
Abstract [en]

The variation and anisotropy in hydraulic conductivity and the coefficient of consolidation was investigated for two Swedish sulphide clays. A series of constant rate of strain oedometer tests was performed on samples trimmed in the vertical and horizontal direction. A methodology to evaluate the horizontal coefficients of consolidation c h via the horizontal hydraulic conductivity k h and the vertical compression modulus M v is proposed. Laboratory evaluations of c h are also compared with determinations of c h from in situ piezometer measurements in vertically drained sulphide clay. Furthermore, the validity of the empirical correlation between hydraulic conductivity change index C k and initial void ratio e 0, C k = 0.5e 0 (Tavenas et al. in Can Geotech J 20(4):645-660, 1983b), was investigated for the sulphide clays. The results from the investigation show large ranges in measured hydraulic conductivities and coefficients of consolidation. However, the results indicate that the correlation C k = 0.5e 0 is valid. The anisotropy in hydraulic conductivity and the coefficient of consolidation of the sulphide clays tested seems to be small. For design purposes, multiple tests for assessment of hydraulic conductivity and the coefficient of consolidation should be made, and a partial factor of safety, depending on the requisite level of safety and the spatial variability of the parameters, should be introduced. For design purposes in this type of clay, k h = k v and c h = c v are suggested.

Place, publisher, year, edition, pages
Springer, 2012
Keyword
Anisotropy, Coefficient of consolidation, CRS test, Hydraulic conductivity, Prefabricated vertical drain, Sulphide clay
National Category
Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-25823 (URN)10.1007/s10706-011-9459-0 (DOI)2-s2.0-84155180932 (Scopus ID)
Note
QC 20120618Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2017-12-12Bibliographically approved
3. Stability for a high embankment founded on sulphide clay
Open this publication in new window or tab >>Stability for a high embankment founded on sulphide clay
2013 (English)In: Proceedings of the Institution of Civil Engeneers: Geotechnical Engineering, ISSN 1353-2618, E-ISSN 1751-8563, Vol. 166, no 1, 31-48 p.Article in journal (Refereed) Published
Abstract [en]

During staged construction of embankments on clay foundations, the undrained shear strength s(u) increases due to consolidation during the construction process. The increase is usually related to the pre-consolidation pressure sigma'(p) by way of the ratio s(u)/sigma'(p) and is important when assessing the stability of an embankment. Properties controlling the increase are usually associated with various unknowns that can be difficult to predict before construction. A case involving a large embankment built on vertically drained sulfide clay is presented. Empirical knowledge and experience of similar constructions on sulfide clay were limited, therefore there were uncertainties of the soil-drain interaction and how the soil would behave under the embankment load. A trial embankment was built to gather knowledge and experience of this particular soil and the observational method was adopted. The study presents how embankment stability was predicted at design stage and controlled during construction. It highlights the importance and usefulness of obtaining measurement data from different types of measurements. Laboratory tests and a large number of in situ tests at different stages during construction were performed to assess s(u)/sigma'(p) ratios in the sulfide clay. The mean s(u)/sigma'(p) ratio was estimated by means of statistical analysis to 0.25 for a large stress interval.

Keyword
embankments, field testing & monitoring, geotechnical engineering
National Category
Civil Engineering Geotechnical Engineering
Identifiers
urn:nbn:se:kth:diva-25824 (URN)10.1680/geng.9.00080 (DOI)000313738500005 ()2-s2.0-84878074873 (Scopus ID)
Note

QC 20130213

Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2017-12-12Bibliographically approved

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