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Proceedings of the Institution of Civil Engineers

Geotechnical Engineering 166 February 2013 Issue GE1

Pages 3148 http://dx.doi.org/10.1680/geng.9.00080

Paper 900080

Received 30/09/2009 Accepted 10/01/2011

Published online 09/02/2012

Keywords: embankments/field testing & monitoring/geotechnical

engineering

ICE Publishing: All rights reserved

Geotechnical Engineering

Volume 166 Issue GE1

Stability for a high embankment founded

on sulfide clay

Muller, Larsson and Westerberg

Stability for a highembankment founded onsulfide clayj1 Rasmus Muller MSc, CEng

Senior Geotechnical Engineer, Tyrens AB, Borlange, Sweden

j2 Stefan Larsson PhD, CEngProfessor, Royal Institute of Technology, Stockholm, Sweden

j3 Bo Westerberg PhD, CEngAssistant Professor, LuleaUniversity of Technology, Lulea, Sweden

j1 j2 j3

During staged construction of embankments on clay foundations, the undrained shear strength su increases due to

consolidation during the construction process. The increase is usually related to the pre-consolidation pressure 9p by

way of the ratio su=9p 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 soildraininteraction 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 su=9p ratios in

the sulfide clay. The mean su=9pratio was estimated by means of statistical analysis to 0 .25 for a large stress interval.

Notationa constant dependent on soil type and failure mode

b constant dependent on soil type

Cc compression indexcv coefficient of consolidation in the vertical direction

C creep index

CPTu cone penetration test with pore pressure

measurement

CRS constant rate of strain oedometer test

CUK0DSS K0 consolidated undrained direct simple shear test

FC fall cone test

FCOED fall cone test on oedometer consolidated samples

FS total factor of safety

FVS field vane shear test

g unit weight

kv vertical hydraulic conductivity

OCR overconsolidation ratio

PVD prefabricated vertical drain

qt cone resistance measured by way of CPTu

SHANSEP stress history and normalised soil engineering

properties

su corrected undrained shear strength

su,FC=FVS undrained shear strength measured via fall cone or

field vane test

USA undrained strength analysisu pore water pressure

wL liquid limit

wm natural water content

9p pre-consolidation pressure

v total vertical stress

9v effective vertical stress

j9 angle of shearing resistance

1. IntroductionDuring construction of a staged embankment founded on clay the

drainage conditions can be classified as partly drained (Ladd,

1991). The weight of the embankment induces positive excess

pore pressures, and consolidation (increase in effective stresses)

is ongoing. If a stability analysis is performed under these

conditions, an analysis in terms of total stresses is usually

preferable (more simple) over an effective stress analysis (Lacasse

et al., 1977; Lambe and Whitman, 1979; Leroueil et al., 2001;

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Wood, 1990). An effective stress analysis requires accuratepredictions of the pore pressure development in the design phase

and very careful control of the development during construction.

Furthermore, an effective stress analysis may overpredict the total

factor of safety (FS). Several recently published studies have

adopted total stress analyses to evaluate stability during staged

construction (e.g. Shibuya et al., 2008; Watabe et al., 2002). A

total stress analysis based on the initial undrained shear strength

su0 in the clay would in most cases be conservative (i.e. lead to

more expensive measures to achieve the required degree of

stability). It is therefore preferable to utilise the increase in su

that occurs owing to consolidation and effective stress increase

during construction, which can be done by way of an undrained

strength analysis (USA) (Ladd, 1991). The basic components of a

USA involve the following principal steps

(a) evaluation of the stress history of the soil in terms of initial

in situ effective stress 9v0 and pre-consolidation stress 9p0

(b) estimation of the changes in stresses imposed by the proposed

loadings by way of consolidation analyses

(c) laboratory tests to evaluate su at different consolidation

stressessu=9p(d) stability analyses using su profiles calculated in step (c).

In order to fulfil step (c) above, the use of K0 consolidated

undrained active and passive triaxial tests and direct simple sheartests is suggested (Ladd, 1991). These tests should be conducted

by way of either the recompression technique (Bjerrum, 1973) or

the stress history and normalised soil engineering properties

(SHANSEP) technique (Jamiolkowski et al., 1985; Ladd and

Foott, 1974). The recompression technique means consolidating

the samples to 9v0 before shearing. The SHANSEP technique

essentially requires consolidating the soil samples to stresses well

beyond9p0 and then unloading them to various overconsolidation

ratios (OCR 9p=9v) before shearing. The limited applicability

of the SHANSEP technique, owing to alteration of the soil

structure, has been the subject of discussion in several studies

(Ladd, 1991; Mesri, 1975; Tavenas and Leroueil, 1980). InSweden the recompression technique is normally adopted in order

to avoid destructuring of the clay (Lofroth, 2008; Westerberg,

1999).

It is common to relate su to 9v and OCR by using the following

constitutive relationship (Ladd and Foott, 1974; Roscoe and

Burland, 1968;Schofield and Wroth, 1968)

su=9v a OCRb1:

where a is dependent on the type of soil and the failure mode

(triaxial compression, direct shear or triaxial extension) and b is

dependent on the type of soil. Typical values of b range from 0.7

to 0.9 with 0.8 being a reasonable estimate for most soils

(Larssonet al., 2007a). Any loading and subsequent consolidation

leading to a stress state where 9v > 9p0 results in a normally

consolidated stress state in the clay where 9v 9p: Equation 1can then be rewritten as

su=9p a2:

For classic limit equilibrium analysis of short-term stability of

embankments, direct simple shear (DSS) tests are suggested as the

most relevant test; these simulate the behaviour around a postulated

failure surface most closely (Wroth, 1984). Several researchers

state that peak strengths from DSS tests provide reasonable

estimates of the average undrained strength ratio (su=9p) along

potential failure surfaces (Ladd, 1991; Larsson, 1980). This

assumption implies a constant value ofa for a certain soil. Values of

aranging from 0.15 to 0.50 have been suggested for different types

of soils in numerous studies (e.g.Chung et al., 2007;Jardine and

Hight, 1987;Karlsson and Viberg, 1967;Kim et al., 2009;Ladd,

1991; Larsson, 1980; Mayne, 1980; Mayne and Mitchell, 1988;

Nicholson and Jardine, 1981; Shibuya et al., 2008; Suzuki and

Yasuhara, 2007; Tanaka, 1994; Watabe et al., 2002). From these

studies it can be concluded that the su=9pratio varies with soil type.

There is usually scatter in obtained values from either in situ tests or

laboratory tests and different test methods in field or laboratory

might render different values. An average value of a 0:22 is

suggested for inorganic clays (Jardine and Hight, 1987;Ladd, 1991;

Larsson, 1980, Mayne, 1980) and a 0:25 for organic clays andsilts (Jardine and Hight, 1987; Ladd, 1991; Larsson, 1980).

Stability analyses, according to the USA methodology used for

designing embankments built using staged construction methods,

require reliable predictions of su at the various stages. The

predictions involve estimations of su=9p, 9v and 9p based on

consolidation analyses. These predictions and consolidation ana-

lyses are, however, associated with uncertainties, thus results

from investigations (i.e. field measurements and laboratory tests)

at a specific site should preferably be supported by experience

from similar projects involving similar ground conditions and

empirical knowledge about the behaviour of the soil in question.

This paper presents how stability during construction was pre-

dicted and controlled in a project involving a large embankment

built on vertically drained sulfide clay in Sweden. USAs based on

predictedsu profiles were used to calculate FS at critical stages of

construction of the embankment. Previous experience of construc-

tion of large embankments on sulfide clay and empirical know-

ledge related to the interaction between vertical drains and this

type of soil was limited. These shortcomings were compensated

for within the design and construction phases by using information

gathered from a trial embankment and the use of the observational

method. Predictions of su used in stability calculations in the

design phase were compared with measurements during construc-

tion. Furthermore, the paper aims at increasing understanding of

the behaviour of sulfide clay with the help of the relationship

su=9p obtained from laboratory tests and evaluated from in situ

measurements ofsu and pore water pressure u during construction.

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2. Description of the projectThe Veda embankment was built to navigate over an approximately

300 m wide valley situated near the river Angermanalven, 55 km

north of the city of Sundsvall in Sweden (Figure 1(a)). This section

is a part of the Adalsbanan railway line which connects the East

coast railway line with the recently built Botnia line along the north-

eastern coast of Sweden. The subsoil strata in the valley generally

consist of soft sediments of silt, clay (partly sulfide clay) and sand.

The embankment was made of crushed rock fill (mainly granite and

gneiss) derived from a nearby tunnelling project, and rises to aheight 16 m above the original ground surface (Figure 1(b)).

Sulfide soils mostly occur in tropical areas around the world.

The occurrence of sulfide soils in Europe is limited, apart from

the coastal areas around the Gulf of Bothnia, where the

embankment is situated (Figure 1(a)). Common to all sulfide

soils is the presence of sulfide in the form of pyrite (FeS 2) and

iron monosulfide (FeS). The sulfide soils that are found in

Sweden around the Gulf of Bothnia usually have a relatively

high organic content as they were formed as organic matter

degraded in fine-grained sediments under anaerobic conditions

(Larsson et al., 2007b). Typical ranges for properties of these

sulfide soils are total sulfur content of 0.12%, total iron

content of 25%, and organic content of 27% of dry weight

(Westerberg and Andersson, 2009). If the sulfide soil is sub-

jected to oxygen (e.g. excavated), there can be negative environ-

mental impacts such as lowering of pH in ground- or surface

water and leaching of metal ions (Macsik, 1999). In Sweden

there are restrictions regarding the handling of sulfide soils, and

excavation should be avoided.

The embankment load imposes a considerable stress increase in

the soil, which in turn leads to deformation and stability

problems. In order to address the stability issues, support berms

consisting of moraine fill were constructed and the embankmentwas built using staged construction, making it possible to account

for the increase in su in the clay due to consolidation effects.

Prefabricated vertical drains (PVDs) were installed in order to

accelerate consolidation. Recently published studies present re-

sults from in situ measurements of the su increase in vertically

drained clay during staged construction of embankments and fills

during land reclamation (Bergado et al., 2002; Bo et al., 2007;

Loet al., 2008;Long and ORiordan, 2001;Suzuki and Yasuhara,

2007). However, as experience of embankments of this particular

magnitude on sulfide clay is limited, uncertainty about strength,

deformation and consolidation characteristics of the subsoil

prevailed. Generally, pilot tests are recommended owing to thecomplexity and difficulty in predicting the parameters required to

make an accurate design of ground improvement works involving

PVDs (Hansbo, 1997). In the present case a trial embankment

was built and instrumented 1 year before the beginning of the

main embankment works. The design and construction processes

were performed according to the observational method (Peck,

1969). Various parameters were monitored during construction of

the embankment, such as su from field vane shear (FVS) tests

and from cone penetration tests (CPTu), and compared with

design assumptions and predictions.

The geotechnical design requirements issued by the client

concerning stability stated that the FS was to exceed 1.5 in both

the short term (during construction) and the long term. In the

present case the critical phase was the short-term situation or, in

other words, the partially drained situation (i.e. partially consoli-

dated), when the consolidation process was ongoing.

Norw

ay

Swed

en

KalixLocation ofsulfide soils

Finlan

dUme

Both

nia

nBay

VedaEmbankment

Sundsvall

Stockholm

Gteborg

0 250 km 500 km

(a)

25

20

15

10

5

0

5

10

15

Elevation:m

0 100 200 300 400

Length: m(b)

Crestofembankment

Original ground surfaceSectionA

SectionB

SectionC

Silty clay

Sulfide clay

Glacial clay

Sand

Moraine

Figure 1.Veda area: (a) location plan (partly fromSchwab, 1976);

(b) elevation through centre of embankment

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3. Initial ground conditionsThe ground surface in the valley was situated about 4 4.5 m

above sea level (Angermanalven river) near the centre of the

embankment. A deposit of clay, silt and sand up to 16 m thick

was present in the bottom of the valley. The sediments overlaid a

firm moraine (Figure 1(b)). The upper 12 m consisted of silty

clay, followed by an approximately 3.5 m thick layer of post-

glacial sulfide clay, which in turn overlaid 35 m of glacial clay

with silt and sand layers. Near hydrostatic pore-water pressures

prevailed corresponding to a water table situated near the ground

surface.

Site investigations in the area consisted of probing, mainly by

way of CPTu, sampling and pore pressure measurements. Labora-

tory tests on undisturbed samples of clay taken from various

depths were also carried out at six locations. Extractions were

made using the Swedish standard piston sampler (SIS, 2007),

pushing the clay sample into 170 mm long plastic tubes with an

inner diameter of 50 mm. Index properties such as liquid limit

wL, natural water content wn and total unit weight were

determined and su was evaluated by fall cone (FC) tests.

Sedimentation analyses were also performed on samples of the

sulfide soil, indicating clay contents (by total weight) of 2732%

and silt contents of 6065%. Total sulfur, iron and organic

contents (by total dry weight) were determined as 0.3 0.4%,

3.1 3.7% and 2.8 2.9% respectively. These ranges fall well intothose presented as typical ranges for sulfide soils, and the soil

was defined as sulfide clay. Furthermore, from samples taken at

two locations, compression index Cc, creep index C, vertical

hydraulic conductivity kv, coefficient of consolidation in the

vertical direction cv and 9p of the clay were determined by way

of constant rate of strain (CRS) consolidation tests and standard

incremental load oedometer tests. Evaluations of su at different

9p were made by FC tests, performed on samples which had

undergone incremental load oedometer tests (FCOED). The

undrained shear strength in the clay was also determined in situ

by way of FVS and evaluated from CPTu.

According to Swedish practice, values of undrained shear strength

in clays evaluated from FC and FVS tests su,FC=FVS or CPTu

should be corrected by empirical relations when used for stability

calculations.

The corrected value of su in overconsolidated clay classified as

normal inorganic Swedish clay is calculated from FC or FVS

tests as (Larsson and Ahnberg, 2005;Larssonet al., 2007a)

su su,FC=FVS43

wL

0:45OCR

1:3

0:15

3:

From CPTu, su is calculated as (Larsson and Ahnberg, 2005;

Larssonet al., 2007a)

su qt v0

13:4 0:0665wLOCR

1:3

0:24:

When the clay is classified as sulfide clay, the corrected value su

is calculated from FC or FVS tests independent of consolidation

status as (Larssonet al., 2007b)

su su,FC=FVS 3 0:655:

From CPTu, su is calculated as (Larssonet al., 2007b)

su q t v0

20

OCR

1:3

0:2

6:

For clays with OCR, 1.3, the last expression in parentheses in

Equations 3, 4 and 6 should be set equal to 1.0. In this study

clays above elevation +4 m and below 1.5 m related to the sea

level, are classified as normal inorganic Swedish clay andbetween +2 m and1.5 m as sulfide clay (Figure 1(b)).

A selection of soil properties along with a typical result from a

CPTu in the area is presented in Figure 2. Profiles showing the

measured initial pore water pressure u0, evaluated 9v0 and 9p0

are also shown. The initial overconsolidation ratio OCR0 was

around 5 at the top of the clay deposit and around 1.3 at the

bottom. In the sulfide clay, Cc, C, wL and wn were significantly

higher while and kv were lower compared to the upper silty

clay and the bottom glacial clay. As seen in Figure 2, the ratio

C=Cc was in the order of 0.060.08 in the sulfide clay. Previous

studies (Mesri and Godlewski, 1977; Mesri et al., 1994) havepresented ratios in the order of 0.050.06. Hence, the evaluated

ratios were a little higher in the sulfide clay at Veda than the

findings for other organic clays presented in the aforementioned

studies.

Typical values of cv were in the range 0.951.4 m2/year over the

relevant stress range (50250 kPa).

There was a relatively large scatter in su obtained from laboratory

FC tests and in situ FVS and CPTu tests. The coefficient of

variation was 2030% in the sulfide clay, in line with the findings

ofLarssonet al. (2007b), and 2070% in the upper silty clay and

the bottom glacial clay. The large scatter in the upper silty clay

and the bottom glacial clay presumably arose from the inhomo-

geneities due to silt and sand layers. Unfortunately, more

sophisticated studies of su, for example by way of triaxial tests or

DSS tests, were not carried out at this stage of the project.

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4. The trial embankment

4.1 Purpose of the trial embankment

Construction of the trial embankment served the purpose of

increasing understanding of strength and deformation properties

in the soil concerning different aspects, such as the ratio su=9pand the consolidation rate in the different clay layers. Further-

more, the trial embankment enabled testing of the equipment and

techniques proposed for measurements of the planned Veda

embankment.

4.2 Description of the trial embankment

In November 2005, PVDs in a triangular pattern with 1.07 m

spacing and instrumentation for the trial embankment were

installed. Drains of the brand Membradrain MD 7007, with a

cross-section of 100 mm 3 3 mm, filter permittivity of 0.3 s1

and a discharge capacity larger than 3 m3/day, were used. The

crest of the trial embankment was situated about 30 m beside the

crest of the Veda embankment, made of crushed rock material

and constructed in two stages. The length and height were 50 m

and 6.7 m respectively (Figure 3).

4

3

2

1 0

1

2

3

4

Elevation:m

4

8

12

Coreresistance,

:MPa

qc

Silty

clay

Sulfide

clay

Glacial

clay

0

10

20

30

40

su0:kPa

FVSFCCPTMean

Design2

0

40

60

80

w

w

n

L

a

nd

:%

wnwLMeanwn

MeanwL

15

17

19

21

:kN/m3 M

ean

0

10

20

30

40

50

kv

10

:m/s(1

)

kvMeankv

0

2040

6080100

u0

v0

and

and

p0:kPa

pu0v0

p0

0

0204060810

Cc

CcMeanCc

00020

040

060

080

10

C

C

MeanC

Figure

2.

Soilp

rofile

and

selected

soilproperties

atthes

ite

before

construction

started

Piezometers

Concrete well

Settlement plate

Inclinometers

T1 T2

0 10 20

Length: m

Section1

Section2

Section3

(a)

Piezo-meters

Berm

Trialembankment

Concretewell Settlement plates

Inclinometers

Berm

PVDs c/c 107 m

15

10

5

0

5

10

15

Elevation:m

20 0 20

Length from centreline: m

(b)

Moraine

Sand

Glacial clay

Sulfide clay

Silty clay

Figure 3.Trial embankment: (a) layout plan; (b) cross-section

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4.3 Measurements and results from the trialembankment

Measurements of settlements, horizontal deformation and pore

pressure development were performed in three sections and

continued for 1 year, until the works with the Veda embankment

started in December 2006.Figure 4illustrates the staged construc-

tion sequence and corresponding measured excess pore pressures

u-excess at different elevations in the soil. Corresponding meas-

urements from different control sections showed good agreement,

therefore mean values are presented. Pore pressure measurements

were conducted with the use of BAT IS piezometers.

Two concrete wells (1.0 m in diameter), T1 and T2, were installed

through the embankment to enable measurements of su during

construction. In situ tests (FVS and CPTu) were made on two

occasions, after 50 days and 140 days. After 220 days, undis-

turbed sampling of the clay using the Swedish standard piston

sampler (SIS, 2007) and subsequent K0 consolidated undrained

direct simple shear tests (CUK0DSS) were performed. The load

from the Veda embankment was expected to induce normally

consolidated stress states at the stages when stability was to be

analysed, that is 9v . 9p0. Hence, evaluation of su at stresses

above 9p0 and with OCR 1 was of interest. Table 1 presents

the evaluated in situ vertical effective stress at the time of

sampling 9v,220, the consolidation stresses used in the tests

9p,DSS, the evaluatedsu values and the obtainedsu=9p ratios. Thesu profiles shown inFigure 5(a)are based on measurements made

50 and 140 days after the beginning of the filling operations,

together with the evaluated mean values from initial tests at the

location of the trial embankment. The profiles were evaluated

based on mean values from tests in wells T1 and T2.Figures 5(b)

and 5(c) show measured u, evaluated 9v and 9p profiles

representing the conditions after 50, 140 and 220 days respec-

tively. The 9v profiles were calculated based on initial stress

conditions, measured u profiles and the total stresses v induced

by the embankment fill ( 18 kN/m3). It can be seen that parts

of the curves representing 9v after 50 and 140 days indicate areas

where the clay was still somewhat overconsolidated. When su=9pratios were evaluated this was taken into account, assigning

b 0:8 in Equation 1 according to the recommendations given

by Larsson et al. (2007a). Evaluated su=9p ratios obtained at

different times and from different test methods ranged from about

0.2 t o 0.45 (Figure 6). Mean values in the sulfide clay were

approximately 0.29 and in the rest of the clay approximately0.33. The coefficient of variation ranged from 0.09 to 0.25 in the

sulfide clay and 0.1 4 t o 0.20 in the other clay layers. Values

chosen for design of the Veda embankment are also presented.

Measurements of ground surface settlements near the crest of the

trial embankment are presented in Figure 7(a). The settlement

plates used were placed on a sand blanket and made of square

steel plates (0.5 m 3 0.5 m) with a steel rod welded to the centre

of the plates. Polyvinyl chloride (PVC) tubes were used to protect

the steel rods from the rock fill. The tips of the rods were

monitored over time by surveying with geodetic total station. In

Figure 7(b), horizontal displacements at different elevations for aselection of time steps are shown. After 1 year, when measure-

ments were interrupted, the crest settlements were in the order of

1.0 1.2 m. Measurement of horizontal displacements was inter-

rupted after about 200 days. At that time, the maximum

horizontal displacement was about 0.17 m and located in the

sulfide clay layer.

4.4 Discussion and conclusions from the trial

embankment

The dissipation of u-excess, that is the consolidation rate, was

much slower in the sulfide clay than in the rest of the clay deposit

(Figures 4 and5(b)). This had an influence on the design of the

PVDs for the Veda embankment, as discussed by Muller and

Larsson (2008). The difference in consolidation rate highly influ-

enced the increase in 9v (and consequently 9p). Hence, the rate

of increase ofsu in the sulfide clay was expected to be lower than

in the silty clay and glacial clay (c.f. Figure 5(a)). As shown in

7

6

5

4

3

2

1

0

Fillheight:m

140

120

100

80

60

40

20

0

u-excess:kPa

0 50 100 150 200 250 300 350 400

Time: days

Load sequenceu-excess at 1 mu-excess at 0 mu-excess at 1 mu-excess at 3 m

Figure 4.Trial embankment: load sequence and measured

u-excess with respect to time

Elevation:m

9v,220:kPa

9p,DSS:kPa

su:kPa

su=9p,DSS

+1 99 120 51.7 0.43

+1 99 180 64.2 0.36

0 63 80 25.7 0.32

0 63 120 37.0 0.31

0 63 180 41.4 0.23

1 113 130 33.3 0.26

1 113 180 37.7 0.21

3 169 160 61.2 0.38

3 169 220 73.2 0.33

Table 1.K0 consolidated undrained direct simple shear test

(CUK0DSS) results

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Figure 5(a), in tests performed after 50 days in the part of the

clay which was still overconsolidated (i.e. 9p 9p0), the su

increase was negligible. According to the pore pressure measure-

ments after 140 days, the clay between elevations +0.5 and

0.5 m should still be somewhat overconsolidated, in other words

a negligible su increase. However, the measurements of su at this

point in time indicated an increase of around 5 kPa (about 30%).

This raised questions regarding the following.

(a) The accuracy of the pore pressure measurements since there

was uncertainty related to the exact positions of the

instruments relative to the drains. Did the measuredu

represent the average value between adjacent drains?

(b) The accuracy of the in situ measurements ofsu:Were the

techniques suitable and were measurements adequately

corrected? Were these instruments suitably positioned for

measurements of average values?

It was concluded that measurements of representative values from

neither piezometers nor CPTu or FVS tests could be expected

from single measurements. Parallel measurements of the same

quantity (u or su), at the same depth but at different locations,

should provide the basis for evaluations of average values.

Furthermore, evaluations of su from measurements by CPTu and

FVS tests should be conducted in parallel. This would enable

estimations of su profiles during construction of the Veda

embankment from three independent sources, CPTu tests, FVS

tests and from pore pressure measurements together with estima-

0 50 100 150 200

v and

p: kPa

v0

p0

v 50 days

p 50 days

v 140 days

p 140 days

v 220 days

(c)

0 10 20 30 40 50 60

su

: kPa

4

3

2

1

0

1

2

3

4

Elevation:m

Initial meanCPT 50 daysFVS 50 daysCPT 140 daysFVS 140 days

(a)

0 40 80 120 160

u: kPa

u0u 50 daysu 140 daysu 220 days

(b)

Figure 5.Trial embankment, evaluated profiles: (a) su; (b) u;

(c) 9v and 9p

0 01 02 03 04 05

su p/

4

3

2

1

0

1

2

3

4

Elevation:m

FVS

CPTu

CUK0DSS

FCOED

Mean

Design

Figure 6.Trial embankment: evaluated su=9p ratio plotted against

depth

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tions of the induced stresses from the embankment and prognoses

of the su=9p ratios.

The choice of design values of su for the stability analyses of the

Veda embankment was uncertain as the scatter in the evaluated

su=9p ratios was quite large. There were no clear trends betweendifferent testing methods, thus no method was regarded as more

reliable than any other. It should be noted that Larsson et al.

(2007b) suggest CPTu as being more reliable than FVS tests. Due

to the uncertainties and considering the suggestions by Larsson

(1980),Jardine and Hight (1987) andLadd (1991), design values

were not strictly evaluated from the mean values (Figure 6).

Values of su=9p ratios corresponding to a cautious estimate were

employed as design values in the stability analyses performed

during the design phase.

5. Preconstruction design of the Vedaembankment

The Veda embankment was designed to be built in seven stages

according to Figure 8. The seventh stage represented unloading

of the surcharge. PVDs installed in a triangular pattern with a

spacing of 0.8 m and large moraine support berms were planned.

The drains were of the same brand as those used at the trial

embankment.Figure 9presents a layout plan and a typical section

of the embankment.

5.1 Preconstruction stability analysis

Construction works were intended to proceed continuously until

completion of stage 5 (Figure 8). Thereafter a 6-month-long

pause was scheduled before applying the surcharge (stage 6). The

most critical phases regarding stability in this project wereidentified when constructing stage 5 and when applying the

surcharge in stage 6.

The geometrical conditions concerning the berm length in com-

parison with the thickness of the clay deposit (Figure 9), and the

occurrence of the significantly weaker sulfide clay layer compared

to the rest of the soil, rendered non-circular slip surfaces with a

significant horizontal translation being least stable. As a result, a

major part of the critical slip surfaces was located beneath the

berms, that is corresponding to a direct simple shear state. In

areas close to the centre of the embankment, su corresponding to

triaxial compression would have been more appropriate due tothe stress rotation. However, su corresponding to triaxial com-

pression is generally significantly larger than su corresponding to

direct simple shearing (e.g.Ladd, 1991). Use of predicted vertical

effective stresses and values of su=9p corresponding to direct

simple shearing were considered as reasonable and conservative

simplifications in this case. In the stability analyses, su profiles

representing the initial conditions (su0) were used in the unim-

proved part of the soil and su profiles corresponding to predicted

design conditions were used where PVDs were installed. Analys-

ing stage 6, two different su profiles were used in the PVD

improved area as the effective stresses were predicted to be

higher below the embankment compared to the support berms,

given the differences in fill heights. The appearance and location

of the critical slip surface representing analyses for stages 5 and

6 is presented in Figure 10. The rock fill embankment and the

moraine support berms were defined as granular materials with

an angle of shearing resistance, j9 348, corresponding to the

0 100 200 300 400

Time: days

0

200

400

600

800

1000

1200

1400

Crests

ettlement:mm

Section 1

Section 2

Section 3

(a)

4

2

0

2

4

6

8

Elevation:m

Section 1, 11 days

Section 1, 56 daysSection 1, 73 days

Section 1, 197 days

Section 3, 11 days

Section 3, 56 days

Section 3, 73 days

Section 3, 197 days

0 40 80 120 160

Horizontal displacement: mm

(b)

Figure 7.Trial embankment: (a) measured settlements and

(b) measured horizontal displacements

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estimated constant voids values. The unit weights of the rock fill

and berm were 18 kN/m3, according to the design code

(Swedish Rail Administration, 2009).

Stability analyses were carried out as analytical calculations by

way of the MorgernsternPrice limit equilibrium method, in the

computer program Beast (Frimann-Clausen, 2003). USAs were

employed to account for the increase in su owing to consolidation

(Ladd, 1991). The vertical effective stress increases in the soil at

different stages of the construction process were evaluated byconsolidation analyses according to the Swedish design guide for

vertical drains (Swedish Road Administration, 1989), based on

the approach presented by Hansbo (1981). Experiences gained

from measurements at the trial embankment were also consid-

ered. The stability analysis for stage 5 was based on the

predictions ofsu after stage 3 (as stages 4 and 5 were intended to

take place continuously). Similarly, stage 6 was based on the

predictions of su after stage 5 and 6 months consolidation time.

The stresses induced by the loading and consolidation process

were expected to render 9v . 9p0 at both stage 5 and 6 through-

out the whole clay deposit. Based on these analyses and the

design su=9p values (Figure 6), predicted su profiles were

obtained (Figure 11). Calculations resulted in FS 1.54 and

FS 1.53 for stages 5 and 6 respectively, the size and shape of

the critical slip surface presented inFigure 10 was valid for both

stages. Corresponding calculations, without accounting for the su

increase, resulted in FS 1.33 and FS 1.02.

A simple parametric study was also performed to check the

sensitivity of the stability to variations in the su=9p values, tan j9

in the rock fill, in the rock fill and the initial su0: The

parametric study was based on normalised values, meaning the

use of the evaluated mean su=9p values (Figure 6),

tan j9 0:675 (348), 18 kN/m3 and the mean su0 profile

(Figure 2). The parameters were varied one at a time by

multipliers of 0.8, 0.9, 1.0, 1.1 and 1.2. Results from the

parametric study are presented in Figure 12, where calculated FS

with different multipliers divided by FSnorm calculated withvalues corresponding to the norm analysis (FS=FSnorm) are

shown. The calculated FS was most sensitive to variations in in

the rock fill (10:8) meaning that an increase (or decrease) in of

10% would render approximately 8% lower (or higher) calculated

FS. The second most influential parameter was the su=9p ratio

(10:6). The stability was least sensitive to variations in tanj9

(10:2) ands u0 (10:2).

6. Construction of the Veda embankment

6.1 Changes in staged construction sequence

Works began in December 2006 when a 0.5 m thick drainage

layer of sand was applied and PVDs installed. Day 0 corresponds

to the start of the actual filling works (stage 1) on 13 March

2007. The load sequence was altered somewhat from the design

(Figure 8). This influenced the stability in mainly two ways: the

higher surcharge (approximately 1 m) introduced a slightly larger

20

18

16

14

12

10

8

6

4

2

0

Fillheight:m

0 100 200 300 400 500 600 700Time: days

200

180

160

140

120

100

80

60

40

20

0

Me

asured

-excess:kPa

u

Stage 6

Stage 5

Stage 4

Stage 3

Stage 2

Stage 1

Load sequence designLoad sequence embankmentLoad sequence bermu-excess at 25u-excess at 10u-excess at 00u-excess at 05u-excess at 20

Figure 8.Veda embankment: loading sequence and measured

u-excess with respect to time

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load, and a rest period (approximately 2 months) initiated

between stages 4 and 5 led to slightly different stress conditions

compared with the intended design. Allowance of a rest period

between stages 4 and 5 enabled some consolidation to take place,

which was accounted for when the stability for stage 5 was

checked during construction.

6.2 Measurements

Regarding the stability of the embankment, the key quantities

were in the rock fill and the su=9p ratio in the clay. An

investigation of existing methods to measure the density or unit

weight in coarse rock fill material was undertaken. However,

owing to time constraints, no suitable method for use in the

present case was found. This quantity was therefore not measured

during the construction works.

Pore pressures were measured continuously throughout the con-

struction process at different levels in the soil (Figure 8).Figures

13(a)13(d) show the evaluated u profiles and 9v profiles under

the embankment and under the berm. The consolidation process

had produced normally consolidated conditions, that is 9v 9p,

for the time steps presented (except after 70 days under the

Trial embankment

100 200 300

A1 B1 C1

A2 B2C2

Piezometers

Concrete well

Settlement plate

Settlement tube

Inclinometers

0 50 100Length: m

(a)

25

20

15

10

5

0

5

10

15

Elevation:m

20 0 20 40 60 80 100 120 140


S.P.: Settlement plateC.W.: Concrete wellINC.: InclinometersS.T.: Settlement tube

Drainage (sand)Original ground surface

Berm (moraine)S.T.S.P.C.W.S.P.

Stage 3Stage 2Stage 1

Embankment (rock fill)

Preloading (rock fill)INC.

C.W.S.P.

S.P.

Moraine

Sand Piezometers

PiezometersSulfide clayGlacial clay

Silty clay

(b)

Stage 6

Stage 5

Stage 4Stage 3

Stage 2

Stage 1

PVD S c/c 08 m

Figure 9.Veda embankment: (a) layout plan; (b) cross-section

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embankment). The predicted (design) u profiles and9v profiles at

stages 5 and 6 are also presented for comparison. For stage 5, it

should be noted that the staged construction sequence was altered

(as described above). The total stresses in the soil were different

when measurements were made (after stage 4) when compared

with the predictions (after stage 3). From the measured u and

calculated v (based on the initial conditions and the prevailing

fill height), profiles of 9v were evaluated. The effect of load

spreading with respect to the limited embankment width and the

limited clay depth was analysed by numerical modelling using a

simple linear-elastic material model, and considered in the

determination ofv.

The undrained shear strength su in the clay was measured by

CPTu and FVS tests in six wells (Figure 9) at the critical

phases during the staged construction process that is, after

130 days (stage 5) and 265 days (stage 6). In addition, FVS

tests were performed after 70 days in the six wells and CPTu

tests were performed after 590 days in the three wells under the

berm (A2, B2 and C2). Evaluated su from tests under the

25

20

15

10

5

0

5

10

15

Elevation:m

20 0 20 40 60 80 100 120 140


Init ial profilesu

Critical slip surface for analysis ofstage 5 and of stage 6

Original ground surfaceand GW surface

34

18 kN/m

3

34

18 kN/m

3

Preloading(rock fill)

Moraine

Sand PVDs c/c 08 m

Sulfide clay

Glacial clay

Silty clay

su profiles withregard to

consolidation

Figure 10.Veda embankment: example of a slip surface analysis,

showing the critical slip surface for stage 5 and stage 6

0 20 40 60 80 100

su: kPa

4

3

2

1

0

1

2

3

4

Elevation:m Initial

Stage 5(embankment and berm)Stage 6 ( )embankmentStage 6 (berm)

Figure 11.Veda embankment: predicted undrained shear

strength su plotted against depth for different stages during

construction

08 09 10 11 12

Multiplier

12

11

10

09

08

FS/FSnorm

su p/

su0

tan

Figure 12.Veda embankment: Calculated FS/FSnorm plotted

against values of the multiplier for different parameters

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embankment and berm are presented in Figures 14(a)14(d).

Calculations of su (su 9v 3 su=9p) based on the evaluated 9vprofiles (Figures 13(b) and 13(d)) and the chosen design su=9pratios (Figure 6) are also presented. In Figures 14(a)14(d) the

predicted (design) su profiles at stages 5 and 6 are also

presented for comparison.

Settlements of the ground surface near the crest of the Veda

0 50 100 150 200 250

u: kPa

4

3

2

1

0

1

2

3

4

Elevation:m

Silty clay

Sulfideclay

Glacial clay

(a) (b)

u0u 70 days,u 130 days (stage 5),Design (stage 5)u 265 days (stage 6),Design (stage 6)

0 50 100 150 200 250

v

: kPa

300

p0

v0

v 70 days

Design (stage 5)

Design (stage 6)

v 130 days (stage 5)


0 50 100 150

u: kPa

4

3

2

1

0

1

2

3

4

Elevation:m

Silty clay

Sulfideclay

Glacial clay

(c) (d)

u0

u, 70 daysu 130 days (stage 5),Design (stage 5)u 265 days (stage 6),Design (stage 6)

0 50 100 150 200 250

v: kPa

p0

v0

v 70 days

Design (stage 5)

Design (stage 6)



u 590 days,

v 590 days

Figure 13.Veda embankment: evaluated measurements of u

and 9v at different stages during construction: (a) uunder

embankment; (b) 9v under embankment; (c) u under berm;

(d) 9v under berm

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embankment are presented in Figure 15(a), and approximately

1.0 1.3 m of settlement was measured after 560 days. InFigures

15(b) and 15(c), horizontal displacements at different elevations

for a selection of time steps are shown. Initially, horizontal

deformations towards the centre of the embankment developed

(negative values inFigures 15(b) and 15(c)). These displacements

occurred due to the construction sequence that is, building the

berms before the embankment in stages 1, 2 and 3 (Figure 8).

CPTu, 590 days

0 20 40 60 80 100

su

: kPa

4

3

2

1

0

1

2

3

4

Elevation:m

Silty clay

Sulfideclay

Glacial clay

(a) (b)

su0FVS, 265 days (stage 6)CPTu, 265 days (stage 6) v us

Design (stage 6)

0 20 40 60 80 100

0 20 60 1004

3

2

1

0

1

2

3

4

Elevation:m

Silty clay

Sulfideclay

Glacial clay

(c) (d)

0 20 40 60 80 100

su

: kPa

su0

FVS, 70 daysFVS, 130 days (stage 5)CPTu, 130 days (stage 5) v us

Design (stage 5)

su: kPa su: kPa

40 80

su0FVS, 265 days (stage 6)

CPTu, 265 days (stage 6) v us

Design (stage 6)

su0

FVS, 70 daysFVS, 130 days (stage 5)CPTu, 130 days (stage 5) v us

Design (stage 5)

p (stage 5) p (stage 6)

p (stage 5) p (stage 6)

Figure 14.Veda embankment: evaluated measurements of su at

different stages during construction; (a) under embankment at

stage 5; (b) under embankment at stage 6; (c) under berm at

stage 5; (d) under berm at stage 6 and after 590 days

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The horizontal displacements changed direction as construction

proceeded, resulting in maximum displacements of approximately

0.05 m and 0.08 m after 560 days. As for the trial embankment,the maximum displacements occurred in the sulfide clay layer.

6.3 Stability calculations

By incorporating the evaluated su profiles, updated calculations

of the total stability were made. These resulted in FS 1.70 and

FS 1.47 for stages 5 and 6 respectively and the stability was

judged as satisfactory at both stages.

7. DiscussionConventional limit equilibrium USAs accounting for strength

increase due to consolidation were performed to assess the

stability of the embankment during construction. As previousexperience and empirical knowledge of these characteristics for

sulfide clay were limited, the observational method was em-

ployed. The stability analyses were most sensitive to variations in

in the rock fill followed by the su=9p ratio in the sulfide clay

(Figure 12). Owing to time constraints, no suitable method of

measuring in the rock fill for use in the present case was

found, and so unfortunately this quantity was not verified during

construction. The value of 18 kN/m3 used was in accordance

with common Swedish practice and should be fairly representa-

tive of actual conditions. This is an issue that is seldom

addressed in embankment projects in Sweden; nevertheless, it

should be the subject of careful consideration in the design and

construction phases of embankment projects. One method for

doing this basically includes excavating a pit in the fill material,

weighing the material, lining the pit with an impermeable sheet

and filling the pit with a known volume of water or sand (e.g.

Bertram, 1973; Gordon and Miller, 1966; ICOLD, 1986; Zeller

and Zeindler, 1957). The increase in su was evaluated from in

situ measurements. An important experience gained from this

project is the value of independent measurement of a certainquantity. The increase in su was estimated from three different

sources and from measurements at six different locations.

Evaluations were made from direct measurements of su (FVS

and CPTu) and indirectly by way of measurements of u in the

clay. All three sources were associated with uncertainties, hence

assumptions and judgements had to be made in order to estimate

the average field conditions. Some of the uncertainties are

presented below.

(a) The positions of the instruments in the drain pattern, as the

vicinity to the drains affected the measured values; this is

also discussed bySuzuki and Yasuhara (2007) andLo et al.(2008). For instance, measurements from a piezometer tip

positioned close to a drain would have indicated a faster

dissipation rate than a tip installed at a larger distance from a

drain. Hence, evaluations ofu from measurements of a single

tip might not have been relevant for a large soil volume.

Furthermore, as a result of consolidation settlements in the

clay, the piezometer tips were to some extent pushed deeper

into the soil. Measurements of the depths of the tips were

made during the consolidation process.

(b) CPTu and FVS tests were considered as tests of relative

values ofsu of the clay. In order to derive design values from

these tests, empirical correction factors were used and the

validity of the design values was therefore dependent on the

validity of these factors. The applicability of correction

factors of clay loaded beyond9p0 is discussed byTavenaset

al. (1978) among others.

(c) Estimations of in the clay and fill material. As seen from

0 100 200 300 400 500 600Time: days

0

200

400

600

800

1000

1200

1400

Crestsettlement:mm

Settlement plate, section A

Settlement plate, section B

Settlement tube, section B

Settlement plate, section C

Settlement tube, section C

(a)

80 40 0 40 80Horizontal displacement: mm

4

2

0

2

6

4

Elevation:m

Section B,41 days

(b)

Section B,76 days

Section B,

254 daysSection B,441 daysSection B,562 days

Section B,140 days

80 40 0 40 80Horizontal displacement: mm

4

2

0

2

6

4

Elevation:m

Section C,41 days

(c)

Section ,76 days

C

Section ,

254 days

C

Section ,441 days

C

Section ,562 days

C

Section ,140 days

C

Figure 15.Veda embankment: (a) measured settlements;

(b) measured horizontal displacements at section B; (c) measured

horizontal displacements at section C

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the simple parametric study, analyses of the stability werestrongly influenced by the assumed value of in the rock fill.

(d) The model used for estimations of load spreading strongly

influenced the assessments of9v, hence the evaluations ofsu

from measurements ofu:

(e) Evaluations of9p0 from CRS tests. For instance, different test

methods or strain rates affect the evaluations (e.g. Olson,

1986).

(f) Estimations of the ratiosu=9p. As seen fromFigure 6and

Figure 16, the scatter in observed values of the ratio were

quite large in this case. It was therefore preferable to compare

measurements with valid empirical relationships.

As seen from Figures 14(a)14(d), evaluations of su from the

three sources agreed fairly well in the sulfide clay. In the silty

clay and in the glacial clay the scatter was larger, presumably

arising from the less homogeneous structure (varves of sand and

silt) of these clays. However, these clay layers had less impact on

the stability. By compiling results from different types of tests

and at different locations, uncertainties in the measurements were

reduced, and a sufficiently reliable assessment of the stability was

enabled.

In this project, su=9p ratios were obtained in the laboratory by

CUK0DSS and FCOED tests. In the field, the su=9p ratios were

obtained by CPTu and FVS tests, and evaluations of 9v bymeasurements of u: Figure 16shows measured su plotted against

evaluated9p in the sulfide clay obtained from the laboratory and

the in situ tests. According to the KolmogorovSmirnov normal-

ity test for the 5% level of significance, the su data for each valueof 9p did not differ significantly from a normal distribution. The

coefficient of variation with respect to the measured su was about

25%, the same order as the coefficient of variation related to the

initial conditions (Figure 2). The uncertainty related to the

positions of the instruments in the drain pattern was probably

reduced by simultaneously measuring at different locations.

In Figure 16, a best linear regression curve of su on 9p by the

method of least squares is shown. Furthermore, the confidence

limits of this regression are shown for the 10% level of signifi-

cance. Since the number of data is large, the confidence limits of

the fitted mean value of su are narrow. The confidence limits of

prediction of the whole sample are considerably larger as

illustrated. The design values of su were set by way of the ratio

su=9p 0:25 for the range 50 kPa , 9p , 250 kPa, which corre-

sponds to a straight line inFigure 16passing through the origin.

As illustrated, the deviation from the best linear regression curve

is very small. Furthermore, according to a t-test, the null

hypothesis that su=9p 0:25 and that the curve passes through

the origin cannot be rejected for the 10% level of significance.

Considering that the sulfide clay has a relatively high organic

content, it is worth noting that the ratio su=9p 0:25 agrees well

with the suggestions in Larsson (1980),Jardine and Hight (1987)

andLadd (1991), regarding organic clay.

In Figures 17(a) and 17(b), recordings of maximum horizontal

displacements (occurring in the sulfide clay layer) are plotted

against crest settlements. Tavenas et al. (1979) suggested a linear

80

70

60

50

40

30

20

10

0

su:kPa

0 50 100 150 200 250 300

p: kPa

Data from field measurements by FVS and CPTuData from laboratory CUK0DSSData from laboratory FCOEDLinear regression, best fitLinear regression, through origo / 025su p Confidence interval for the best-fit regression90% limit of prediction

Figure 16.Variation in undrained shear strength su plotted

against evaluated preconsolidation stress 9p

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increase in maximum horizontal displacement dh with the crest

settlement ds, with a mean of 0.16 based on 13 case history

embankments on soft clay sites. Ratios of dh=ds were suggested

as: 0.18 for overconsolidated clays; 1.0 during construction

for normally consolidated clays (undrained distortion); and0.16

during initial consolidation for normally consolidated clays. At

the Veda embankment, after development of the initial negative

horizontal displacements, dh=ds was approximately 0.060.14

and gradually increased to 0.140.19. At the trial embankment

dh=ds was approximately 0.150.18 during the whole construc-

tion process. These findings correspond rather well with the

suggestions by Tavenas et al. (1979) regarding deformation of anormally consolidated clay under the stresses imposed by

embankments.

7. ConclusionMeasurements during construction aimed to compensate for

uncertainties in the design assumptions. Uncertainties were

compensated for by evaluating a given property by way of a

number of different measurement methods and at different

locations.

The utilisation of shear strength increase, according to the ratio

su=9

p, was possible because of the information gained from thetrial embankment and laboratory tests in combination with the

use of the observational method. A controllable design was

possible without too much in-built safety.

The large amount of measurements during construction showed

that the ratio su=9p 0.25 is valid for a large stress interval.

Since the scatter is considerable, use of a single test or only a

few tests can result in misleading conclusions.

AcknowledgementsThe authors wish to express their thanks to the Sven Tyrens

Foundation for making this study possible and to Adalsbanan

Railroad Line for allowing the use of all measurements presented

in this paper. Mrs Tara Wood at the Chalmers University of

Technology is also acknowledged for proofreading and valuable

comments on the text.

REFERENCES

Bergado DT, Balasubramanian AS, Fannin RJ and Holtz RD

(2002) Prefabricated vertical drains (PVDs) in soft Bangkok

clay: a case study of the new Bangkok International Airport

project. Canadian Geotechnical Journal39(2): 304315.

Bertram GE(1973) Field tests for compacted rockfill. In

Embankment Dam Engineering, Casagrande Volume(Hirschfeld RC and Poulos SJ (eds)). Wiley, New York, NY,

pp. 120.

Bjerrum L (1973) Problems of soil mechanics and construction on

soft clays: SOA Report. Proceedings of the 8th International

Conference on Soil Mechanics and Foundation Engineering,

Moscow 3: 111159.

Bo MW, Arulrajah A and Nikraz H (2007) Preloading and

prefabricated vertical drains design for foreshore land

reclamation projects: a case study. Ground Improvement

11(2): 6776.

Chung SG, Kim GJ, Kim MS and Ryu CK (2007) Undrained shear

strength from field vane tests on Busan Clay. Marine

Georesources and Geotechnology 25(34): 167179.

Frimann-Clausen CJ (ed.)(2003)BEAST a Computer Program

for Limit Equilibrium Analysis by the Method of Slices,

revision 4. Roquefort les Pins.

Gordon BB and Miller RK (1966) Control of earth and rock-fill

0 250 500 750 1000 1250 1500

Crest settlement: mm

200

150

100

50

0

50

100

Maxim

um

horizontaldisplacement:mm

Section BSection Cd /d 016*h s

*Tavenas . (1979)et al

(a)

0 250 500 750 1000 1250 1500

Crest settlement: mm

200

150

100

50

0

50

100

Maximum

horizontaldisplacement:mm

Section 1Section 3d /d 016*h s

*Tavenas . (1979)et al

(b)

Figure 17.Veda embankment: measured maximum horizontal

displacement plotted against crest settlements: (a) Veda

embankment; (b) trial embankment.Tavenas et al.(1979) mean

ratio of dh/ds 0.16 is based on 13 case history embankments

on soft clay sites

46




on sulfide clay


8/12/2019 geng166-0031

17/18

for Oroville Dam. Journal of the Soil Mechanics andFoundation Division, ASCE92(3): 123.

Hansbo S(1981) Consolidation of fine-grained soils by

prefabricated vertical drains. Proceedings of the 10th

International Conference on Soil Mechanics and Foundation

Engineering, Stockholm 3: 667682.

Hansbo S(1997) Practical aspects of vertical drain design.

Proceedings of the 14th International Conference on Soil

Mechanics and Foundation Engineering, Hamburg3: 1749

1752.

ICOLD (International Commission on Large Dams) (1986)Quality

Control for Fill Dams. ICOLD, Paris, Bulletin No. 56,

Appendix B.

Jamiolkowski M, Ladd CC, Germaine JT and Lancelotta R (1985)

New developments in field and laboratory testing of soils.

Proceedings of the 11th International Conference on Soil

Mechanics and Foundation Engineering, San Francisco, vol.

1, pp. 57153.

Jardine RJ and Hight DW (1987) The behaviour and analysis of

embankments on soft clays. In Embankments on Soft Clays

(Jardine RJ and Hight DW (eds)). Public Works Research

Centre, Athens, Greece, pp. 159244.

Karlsson R and Viberg L (1967)Ratio c/p9 in Relation to Liquid

Limit and Plasticity Index, with Special Reference to Swedish

Clays. Swedish Geotechnical Institute, Stockholm, Sweden

Preliminary Report, 23, pp. 4347.Kim C, Kim S and Lee J (2009) Estimating clay undrained shear

strength using CPTu results. Proceedings of the Institution

of Civil Engineers Geotechnical Engineering162(2):

119127.

Lacasse SM, Ladd CC and Barsvary AK (1977) Undrained

behaviour of embankments on New Liscard varved clay.

Canadian Geotechnical Journal14(3): 367388.

Ladd CC(1991) Stability evaluation during staged construction.

Journal of Geotechnical Engineering (22nd Terzaghi

Lecture), ASCE117(4): 537 615.

Ladd CC and Foott R(1974) New design procedure for stability

of soft clays. Journal of the Geotechnical EngineeringDivision, ASCE100(7): 763786.

Lambe TW and Whitman RV (eds) (1979)Soil Mechanics, SI

Version. Wiley, New York, NY, USA.

Larsson R(1980) Undrained shear strength in stability calculation

of embankments and foundations on soft clays. Canadian

Geotechnical Journal17(4): 591 602.

Larsson R and Ahnberg H (2005) On the evaluation of undrained

shear strength and preconsolidation pressure from common

field tests in clay. Canadian Geotechnical Journal42(4):

12211231.

Larsson R, Sallfors G, Bengtsson P-E et al. (2007a) Evaluation

of Shear Strength in Cohesive Soils with Special Reference

to Swedish Practice and Experience. Swedish

Geotechnical Institute, Linkoping, Sweden, Information No. 3

(in Swedish).

Larsson R, Westerberg B, Albing D, Knutsson S and Carlsson E

(2007b)Sulphide Soil Geotechnical Classification and

Undrained Shear Strength. Swedish Geotechnical Institute,Linkoping, Sweden, Report No. 69 (in Swedish).

Leroueil S, Demers D and Saihi F (2001) Considerations on

stability of embankments on clay. Soils and Foundations

41(5): 117127.

Lo SR, Mak J, Gnanendran CT, Zhang R and Manivannan G

(2008) Long-term performance of a wide embankment on

soft clay improved with prefabricated vertical drains.


Lofroth H (2008) Undrained Shear Strength in Clay Slopes

Influence of Stress Conditions. A Model and Test Study. Swedish

Geotechnical Institute, Linkoping, Sweden, Report No. 71.

Long MM and ORiordan NJ (2001) Field behaviour of very soft

clays at the Athlone embankments. Geotechnique51(4):

293309.

Macsik J(1999) Soil Improvement Based on Environmental

Geotechnics, Environmental and Geotechnical Aspects of

Drainage of Redox-sensitive Soils and Stabilisation of Soils

with By-products. PhD thesis, LuleaUniversity of

Technology Division of Mining and Geotechnical

Engineering, Lulea, Sweden, doctoral thesis No. 1999:09.

Mayne PW(1980) Cam-Clay predictions of undrained strength.

Journal of the Geotechnical Engineering Division, ASCE

106(11): 1219 1242.

Mayne PW and Mitchell JK (1988) Profiling of overconsolidation

ratio in clays with field vane. Canadian Geotechnical Journal25(1): 150157.

Mesri G(1975) New design procedure for stability of soft clays.

Discussion.Journal of the Geotechnical Engineering

Division, ASCE101(4): 409412.

Mesri G and Godlewski PM (1977) Time- and stress-

compressibility interrelationships. Journal of the

Geotechnical Engineering Division, ASCE103(5): 417429.

Mesri G, Kwan Lo DO and Feng TW (1994) Settlement of

Embankments on Soft Clays. American Society of Civil

Engineers, Reston, VI, USA, Geotechnical Special

Publication 40, pp. 856.

Muller R and Larsson S (2008) Veda trial embankment comparison between measured and calculated deformations

and pore pressure development. Proceedings of the 2nd

International Workshop on Geotechnics of Soft Soils: Focus

on Ground Improvement(Karstunen M and Leoni M (eds)).

Taylor and Francis, London, UK, pp. 405 410.

Nicholson DP and Jardine RJ (1981) Performance of vertical

drains at Queenborough bypass. Geotechnique 31(1): 67 90.

Olson RE(1986)State of the Art: Consolidation Testing.

American Society for Testing and Materials, West

Conshohocken, PA, USA, STP 892, pp. 770.

Peck RB(1969) Advantages and limitations of the observational

method in applied soil mechanics (Ninth Rankine Lecture).

Geotechnique 19(2): 171187.

Roscoe KH and Burland JB (1968) On the generalised stress

strain behaviour of wet clay. Proceedings of the Symposium

on Engineering Plasticity. University Press, Cambridge, UK,

pp. 535 609.

47




on sulfide clay


8/12/2019 geng166-0031

18/18

Schofield AN and Wroth CP (eds) (1968)Critical State SoilMechanics. McGraw Hill, London, UK.

Schwab EF(1976) Bearing Capacity, Strength and Deformation

Behaviour of Soft Organic Sulphide Soils. Royal Institute of

Technology Division of Soil and Rock Mechanics,

Stockholm, Sweden.

Shibuya S, Jung M, Chae J and Fujiwara T (2008) Evaluation of

short-term stability for sea-wall structure at Kobe airport.

Journal of Civil Engineering, KSCE12(3): 155163.

SIS (Swedish Standards Institute)(2007) Geotechnical

Investigation and Testing Sampling Methods and

Groundwater Measurements Part 1: Technical Principles

for Execution. SIS, Stockholm, Sweden, SS-EN ISO 22475

1:2006.

Suzuki K and Yasuhara K (2007) Increase in undrained shear

strength of clay with respect to rate of consolidation.Soils

and Foundations 47(2): 303318.

Swedish Rail Administration(2009) TK Geo. Swedish Rail

Administration, Borlange, Sweden, BVH 1585.001 (in

Swedish).

Swedish Road Administration(1989) Vertical Drains Design

Guide. Swedish Road Administration, Borlange, Sweden,

Publication 1987:30 (in Swedish).

Tanaka H(1994) Vane shear strength of a Japanese marine clay

and applicability of Bjerrums correction factor. Soils and

Foundations 34(3): 39 47.Tavenas F and Leroueil S (1980) The behaviour of embankments

on clay foundations. Canadian Geotechnical Journal17(2):

236260.

Tavenas F, Blanchet R, Garneu R and Leroueil S (1978) Thestability of staged-constructed embankments on soft clays.


Tavenas F, Mieussens C and Bourges F (1979) Lateral

displacements in clay foundations under embankments.


Watabe Y, Tsuchida T and Adachi K (2002) Undrained shear

strength of Pleistocene Clay in Osaka Bay. Journal of

Geotechnical and Geoenvironmental Engineering, ASCE

128(3): 216226.

Westerberg B(1999) Behaviour and Modelling of a Natural

Soft Clay Triaxial Testing, Constitutive Relations and

Finite Element Modelling. PhD thesis, LuleaUniversity

of Technology Division of Mining and Geotechnical

Engineering, Lulea, Sweden, doctoral thesis no.

1999:13.

Westerberg B and Andersson M(2009) Undrained shear strength

and compression properties of Swedish fine-grained sulphide

soils. Proceedings of the 17th International Conference on

Soil Mechanics and Geotechnical Engineering, Alexandria,

vol. 1, pp. 7275.

Wood DM (ed.) (1990) Soil Behaviour and Critical State Soil

Mechanics. Cambridge University Press, Cambridge, UK.

Wroth CP(1984) The interpretation of in situ soil tests (24th

Rankine Lecture). Geotechnique 34(4): 449489.

Zeller J and Zeindler H (1957) Test fills with coarse shellmaterials for Goschenenalp Dam. Proceedings of the 4th

International Conference on Soil Mechanics and Foundation

Engineering, London 2: 405409.

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