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Stability for a high embankment founded on sulphide clay
Tyréns AB.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.ORCID iD: 0000-0001-9615-4861
Luleå Institute of Technology.
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.

Place, publisher, year, edition, pages
2013. Vol. 166, no 1, 31-48 p.
Keyword [en]
embankments, field testing & monitoring, geotechnical engineering
National Category
Civil Engineering Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-25824DOI: 10.1680/geng.9.00080ISI: 000313738500005Scopus ID: 2-s2.0-84878074873OAI: oai:DiVA.org:kth-25824DiVA: diva2:359975
Note

QC 20130213

Available from: 2010-11-01 Created: 2010-11-01 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Embankments founded on sulphide clay: - some aspects related to ground improvement by vertical drains
Open this publication in new window or tab >>Embankments founded on sulphide clay: - some aspects related to ground improvement by vertical drains
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
geotechnical engineering; embankments; vertical drains; sulphide clay
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-25802 (URN)
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
2. Probabilistic stability analysis of embankments founded on clay
Open this publication in new window or tab >>Probabilistic stability analysis of embankments founded on clay
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xviii, 74 p.
Series
Trita-JOB PHD, ISSN 1650-9501 ; 1018
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-122886 (URN)
Public defence
2013-06-04, Sal B1, Brinellvägen 23, Brinellvägen 23, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20130529

Available from: 2013-05-29 Created: 2013-05-29 Last updated: 2013-05-29Bibliographically approved

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