Gaudin2011

Recent contributions of geotechnical centrifuge modelling to the
understanding of jack-up spudcan behaviour
Christophe Gaudin, Mark Jason Cassidy n
, Britta Bienen, Muhammad Shazzad Hossain
Centre for Offshore Foundation Systems, University of Western Australia, Perth, WA 6009, Australia
a r t i c l e i n f o
Available online 17 January 2011
Keywords:
Geotechnical engineering
Offshore foundations
Centrifuge modelling
Spudcan
Jack-up
Soil–structure interaction
a b s t r a c t
The paper presents an overview of the recent contributions of centrifuge modelling to the understanding
of soil–structure interaction and the development of design and predictive methods in the field of mobile
jack-up drilling rig foundations. Both advantages and limitations of the centrifuge methods are detailed
and key examples are presented. The benefits provided by centrifuge modelling to the development of
analysis methods that are now being used within the jack-up industry are highlighted. To conclude,
industry trends and research opportunities are discussed, as is the possible role of the geotechnical
centrifuge in finding solutions to these new needs.
& 2010 Elsevier Ltd. All rights reserved.
1. Introduction
In the offshore oil and gas industry, most drilling operations in
water depths up to around 120 m are performed from self-elevat-
ing mobile jack-up units. These offshore platforms typically have
a buoyant triangular hull, three independent truss-work legs and
foundations, commonly known as ‘spudcans’, that approximate large
inverted cones. For jack-up installation and removal from site, a rack
and pinion system are used to jack the legs up and down through the
deck (Fig. 1). Roughly circular in plan, spudcans typically have a
shallow conical underside (in the order of 15–301 to the horizontal),
some with a sharp protruding spigot. In the larger jack-ups in use
today, the spudcans can be in excess of 20 m in diameter, with shapes
varying with manufacturer and rig. As an alternative, some jack-ups
use a mat support that connects all of the legs together. These have
applicability in very soft sediments, because of the increased bearing
area of the mat. Jack-up leg lengths are in the order of 100–205 m.
Jack-up rigs are self-installing. They are towed to site with their
legs elevated out of the water. On location, their legs are lowered to
rest on the seabed. Once the jack-up has been positioned, the
spudcans are jacked until an adequate bearing capacity exists for
the hull to be lifted clear of the water. The spudcan foundations are
then preloaded by pumping sea-water into the ballast tanks in the
hull. This ‘proof tests’ the foundations by exposing them to a larger
vertical load than the spudcan’s proportion of the rig’s self-weight
(usually by a factor of 1.3–2). The ballast tanks are emptied before
drilling operations begin.
During the preloading process, challenges faced by the geotech-
nical engineer include an accurate prediction of the penetration depth
and ensuring the stability of the jack-up during penetration. Instabil-
itiescan occur duetoeccentricloadingofthespudcans bya slopeor an
existing footprint on the seabed, or by a rapid leg penetration during a
‘punch-through’ failure. In the latter, the spudcan temporarily loses
vertical capacity as it punches through a layer of stronger soil into
underlaying softer conditions.
After the jack-up has been installed, it typically operates at the site
for as little as days or as long as a number of years. Engineers must
assess the jack-up stability during this operational phase prior to rig
installation, with the major issue being capacity under storm loading.
During a storm, environmental wind, wave and current forces impose
horizontal, moments and even torsional loads on the spudcans, as
well as altering the vertical load sharing between the spudcans.
Geotechnical engineers must be able to describe the behaviour of
spudcan footings to these combined loads.
When the jack-up is to be finally moved from the site, the
spudcan footings must be removed from the ground. Deep pene-
trations can make this operation difficult, with the time to pull the
spudcans clear being reported to exceed one month in extreme
circumstances. There is an industry need for better understanding
of the extraction mechanisms and the development of a more
efficient extraction procedure.
Before a jack-up can operate at a given location, a site-specific
assessment of its installation, operation and extraction must be
performed. This on-going assessment is what differentiates the
jack-up analysis from that of the conventional fixed platforms and
most onshore operations. The ‘‘Guidelines for the Site Specific
Assessment of Mobile Jack-Up Units’’ as published by Society of
Naval Architects and Marine Engineers (SNAME) has been the
accepted as an industry standard (SNAME, 1994, 2008), though
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/oceaneng
Ocean Engineering
0029-8018/$ - see front matter & 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.oceaneng.2010.12.001
n
Corresponding author. Tel.: +61 8 6488 3732; fax: +61 8 6488 1044.
E-mail addresses: gaudin@civil.uwa.edu.au (C. Gaudin),
mark.cassidy@uwa.edu.au (M.J. Cassidy), britta.bienen@uwa.edu.au (B. Bienen),
hossain@civil.uwa.edu.au (M.S. Hossain).
Ocean Engineering 38 (2011) 900–914

more recently an International Standard Organisation (ISO) docu-
ment has been drafted (ISO, 2009). These documents have been
significantly enhanced by analysis methods developed through
centrifuge testing, with example details provided in this paper.
The more recent InSafeJIP is updating industry guidelines for the
installation and removal of jack-ups (Osborne et al., 2008, 2009). A
key task of the InSafeJIP is to verify analytical models developed
against offshore in-situ field records. This includes methods
developed through centrifuge experiments initially at Cambridge
and Manchester Universities, but more recently at the University of
Western Australia and the National University of Singapore.
1.1. Aims of the paper
Centrifuge modelling is now a well established modelling techni-
que within the geotechnical community and has been used for decades
to provide insights into soil behaviour and soil–structure interaction.
The benefits of the centrifuge to model jack-up foundations were
addressed in some detail when Martin (2001) presented a state-of-the-
art report on the impact of centrifuge modelling in offshore geotech-
nics.Sincethisreview in2001, experimentaltestinginthegeotechnical
centrifuge has contributed to new insights, predictive methods and
design guidelines in all three areas of installation, operation and
extraction. A selection of examples is presented in this paper.
After an introduction to the principles, advantages and limita-
tions of centrifuge modelling, the examples are presented. These
further develop the issues highlighted in this introduction, discuss
centrifuge technologies, present research outcomes and highlight
applications within the jack-up industry. All of these themes are
also summarised in Table 1. The example contributions provided
are organised following the three distinct phases of jack-up
operations: installation of the jack-up, capacity under storm
loading during operation and removal of the jack-up.
Due to the space limitations of a journal paper, some of the
significant contributions of the centrifuge made prior to 2001 and
some that pertain to particular issues are not covered. Notably, this
includes a thorough coverage of the research establishing spudcan
yield surface approaches on the Cambridge centrifuge (see Dean
et al., 1993, Wong et al., 1993 amongst others), the bearing capacity of
spudcans in silica and calcareous sands (e.g. Finnie and Randolph,
1994; Dean et al., 1993; Teh et al., 2006; White et al., 2008), the inter-
action between a spudcan during installation and the nearby piles of a
fixed jacket platform (e.g. Siciliano et al., 1990; Leung et al., 2006,
2008; Xie et al., 2006, 2010) and the contributions of Ng and Lee
(2002) to predicting spudcan settlements under cyclic loading. Other
issues, such as predicting the dynamic motion of jack-ups, spudcan
scour and creep settlements, are also important to the design and
site-specific assessment of jack-ups, but are beyond the scope of
this paper.
2. Centrifuge modelling
2.1. Principles of centrifuge modelling
The constitutive behaviour of soil is highly non-linear and stress
level dependent. To simulate accurately in a physical model
(commonly called model), the behaviour of a full scale geotechnical
structure (commonly called prototype) and the in-situ stresses
must be reproduced in the model. This is achieved by subjecting the
model to a centrifuge acceleration; increasing the self-weight of the
soil by the ratio of the centrifuge acceleration to the Earth’s gravity
(see Fig. 2). This ratio, denoted n, is the multiplicative scaling factor
required to convert dimensions in a centrifuge model to the dimen-
sions of the corresponding field scale situation. Hence, stresses s in
theprototypeat adepthzp, expressed as s¼rgzp,areequivalent tothe
stresses in the model at a depth zm¼zp/n, which are expressed as
s¼rngzm. Because the inertia acceleration field is given by o2
R
(where R is the radius of the centrifuge acceleration and o the angular
rotational velocity), the variation of stress with depth in the model
varies slightly compared to the linear variation with depth in the
prototype (see Fig. 3). However, this is accounted for in the inter-
pretation of centrifuge modelling results. General descriptions of
centrifuge modelling are provided by Schofield (1980), Taylor (1995)
and Muir Wood (2004). Similitude principles and scaling laws
required to extrapolate model dimensions to prototype dimensions
are developed in Garnier et al. (2007).
2.2. Advantages of centrifuge methods in investigating spudcan–soil
interaction
Centrifuge methods offer the following benefits that are rele-
vant to jack-up unit spudcan foundations:
Correct simulation of soil effective stress and soil stiffness: this is
required to realistically simulate soil stress–strain behaviour
around the spudcan.
Shortened time frames: the centrifuge requires a relatively small
volume of soil, limiting the time required for sample preparation.
For soft soil, the primary consolidation may be further shortened
by self-weight consolidation under the gravitational acceleration.
Similarly, testing sequences are considerably shortened though
still ensuring the correct drainage conditions. This allows data to
be collected in a short time frame and at cost orders of magnitude
lower than those associated with field testing. Typically, a series of
six to ten tests in the centrifuge can be undertaken within
Fig. 1. Example of jack-up unit and spudcan foundation (after Le Tirant, 1979).
C. Gaudin et al. / Ocean Engineering 38 (2011) 900–914 901

2–3 weeks, including the soil sample preparation. With an ability
to cover a wide variety of loading and/or soil conditions, the
centrifuge also provides the ability to conduct parametric studies.
Controlled seabed reconstitution: control of the soil reconstitu-
tion process results in a homogeneous sample, with known
boundary conditions and stress history. By using standard soil
characterisation tools in controlled conditions (such as cone
penetrometer tests, shear vane tests and more recently T-bar
penetrometer tests for soft soils (see Randolph, 2004)), and
post-testing soil classification methods (such as particle size
distribution or Atterberg limits performed on core samples
taken from the centrifuge samples), it is possible to determine
the soil characteristics accurately. Since boundary conditions,
material properties and soil stress history are well controlled in
centrifuge models, quantitative results of the penetration
resistance and patterns of soil flow may be used to validate
numerical or analytical models rigorously.
Realistic loading conditions: new motion control techniques are
able to accurately replicate complex loading sequences, including
cyclic vertical or/and horizontal motion/s under either load or
displacement control. This is particularly relevant to combined
loading conditions generated by the environmental loading during
jack-up operation, or during re-installation events near existing
footprints.
Detailed instrumentation and analysis techniques: new insights
into spudcan behaviour have been derived by improved
Table 1
Some recent contributions to the spudcan modelling through centrifuge testing and future requirements.
Example Problem
addressed
Centrifuge technology used Insights/outcomes Application in industry Future requirements
1 Installation in
clays:
deep
penetration
back flow
PIV and photogrammetry
Accurate load–displacement
measurements
Definition of transition
from shallow to deep
mechanisms
Method for predicting the
depth at which flow-
around mechanism occurs
New bearing capacity
formulae that account for
deep penetration, as well as
rate and sensitivity
New design charts and formula for
predicting preferential flow
mechanism, as implemented in
draft ISO (2009)
Tests with varying soil
sensitivity
Application into soils with
intermediate drainage
conditions
Assessing capacity increase
and settlement, due to
dissipation of pore-
pressures during and after
preloading
2 Spudcan punch-
through
stiff-over-
soft clay
sand-over-
clay
measurements
Miniature ball penetrometers
(Fig. 18)
Definition of
punch—through
mechanisms
Underpinning of analytical
prediction methods
New methods being trialled in
industry, such as in InSafeJIP
(Osborne et al., 2009)
Testing in more complex
multi-layered soils
Comparison with field
measurements
Direct predictive methods
based on in-situ
penetrometer data
Application in
unconventional soils, such
as cemented hard layers
3 Reinstallation
into existing
footprints
Shortened drainage conditions
allowed for years of prototype
drainage between footprint
creation and reinstallation
Parametric study on footprint
geometry and degree of strength
disturbance/setup
Multiple testing sites
Miniature ball penetrometers
Guidance on critical
reinstallation offset
distance
Understanding of relative
footprint geometry and
strength disturbance
contribution
Providing some evidence to the
qualitative recommendations of
reinstallation offset distance in
draft ISO (2009) guidelines
Accounting for the
structural configuration
(stiffness at the hull level)
Investigating mitigation
methods, such as skirted
spudcans
4–5 Combined VHM
capacity and
jack-up ‘‘fixity’’
behaviour
measurements
Scale model of three-legged
jack-up (Fig. 13)
Verification of VHM yield
capacity surfaces at stress
levels relevant to field
spudcan footings
Validation of numerical
VHM force-resultant
models for pushover
analysis in multi-footing
structures
Force-resultant models allowed for
in step 3 analysis of SNAME (2008)
and draft ISO (2009) guidelines
Cyclic loading
Multiple degree-of-
freedom loading arms for
use in centrifuge
Dynamic loading tests
and models
Soft soils and intermediate
silty soils to be tested
Capacity of deeply
embedded spudcans
and legs
6–7 Spudcan
extraction
Pore-pressure and total stress
transducers
Water jetting, using a syringe
pump (Fig. 16)
Mechanisms governing
extraction, including
additional capacity due to
consolidation during long
operations
New methodology for
predicting extraction
resistance whilst using
water jetting
InSafeJIP (2009, 2010) Extend current
methodology for deep
embedment
Investigating performance
of top jetting
Investigating performance
of cyclic extraction
C. Gaudin et al. / Ocean Engineering 38 (2011) 900–914902

instrumentation developed for centrifuge modelling. For
instance, by using visual image acquisition systems (such as
digital camera) and associated image processing systems (such as
particle image velocimetry (PIV), and photogrammetry, described
for application to geotechnics by White et al. (2003)), soil flow
mechanisms evolving with spudcan penetration have provided
the basis for a number of new predictive models. Accurate and
detailed miniature pore pressure and total pressure measure-
ments have also provided insights into mechanisms generating
excess or negative pore-pressures at the spudcan surface.
2.3. Potential limitations of centrifuge methods in investigating
spudcan–soil interaction
As in any experimental technique, centrifuge modelling has
limitations. Common centrifuge limitations include potential scale
effects, difficulties in modelling secondary consolidation and shear
strain localisation (see Gaudin et al., 2010b). The following addi-
tional three limitations are of particular relevance to the centrifuge
modelling of jack-up spudcan behaviour.
Jack-up operations are increasingly being mobilised in regions
with highly stratified seabeds and complex soils that exhibit
intermediate drainage conditions, high sensitivity and sometimes
have high carbonate content. These conditions are still difficult to
model in the centrifuge, where single soil stratigraphy remains
dominant and where artificial soils usually exhibit low sensitivity.
The complex soil–structure interaction resulting from the inter-
action between the three jack-up legs is in most cases ignored, with
single leg models still the most commonly tested. Notable excep-
tions are the three-legged jack-up models tested by Murff et al.
(1991), Dean et al. (1995, 1996, 1998) and Bienen et al. (2009a).
The variation of centrifuge acceleration with sample depth may
be a limitation in centrifuges with small radius (lower than 1 m),
due to the large penetration depth involved in jack-up founda-
tions installation in soft soils.
Despite these potential limitations, centrifuge methods have
been used extensively to investigate the behaviour and perfor-
mance of jack-up foundations, providing insight and data used to
develop industry guidelines and procedures (such as SNAME (1994,
2008) and ISO (2009)). As such, centrifuge methods have been used
primarily to establish fundamental understanding of jack-up
foundation behaviour and derive assessment methods, rather than
to directly test specifics of an offshore jack-up operation at one
particular field.
2.4. History of contributions and impact on design practices in
offshore geotechnics
The initial use of centrifuge modelling in offshore geotechnics
took place at the Manchester University in 1973, where the
behaviour and performance of gravity platforms for use in the
Gulf of Mexico were investigated (Rowe and Craig, 1981). The work
encompassed a wide range of soil and loading conditions and
provided pivotal insights taking place into the failure mechanism
(Craig and Al-Saoudi, 1981). In the early days of the centrifuge, it
was understood and acknowledged that centrifuge modelling
could significantly contribute to design when novel conditions,
or those not fully understood, prevailed (Craig, 1984).
Since the pioneering work in 1973 centrifuge research has expan-
ded worldwide, initially under the impulsion of Professor Schofield in
Europe and Professor Kimura in Japan. Initially, research focused first
on phenomenological and site specific studies before progressively
developing towards more general studies, including the observation
of failure mechanisms and the understanding of soil–structure
interaction. Eventually, it aided the development of predictive design
methods. This marked the transition from the centrifuge modelling to
the centrifuge testing. The former aims at establishing the validity/
relevance of certain assumptions, designs or models, by directly
replicating the field conditions. In this case, the results provide an
immediate representation of the design situation. Centrifuge testing,
on the other hand, creates an idealised representation of a problem in
order to obtain quantitative or/and qualitative prediction/s about the
mode of behaviour of the structure investigated (Lee, 2001).
As geotechnical centrifuge techniques developed technically and
scientifically, and with an increased need for performance data and
understanding of offshore soil–structure interaction, the acceptance
of the offshore community to the benefits of the centrifuge grew
significantly. An important step in this process was the keynote
address given by Professor Murff to the wider offshore community, at
the Offshore Technology Conference (Murff, 1996). It advocated the
benefits of centrifuge methods by providing key examples, notably
related to suction caissons, drag anchors and jack-up foundations. The
latter example mainly discussed the research on jack-up foundations
sponsored by Exxon and performed in the Cambridge University
centrifuge, and also at the Oxford University (final report: Noble
Denton and Associates, 1987). The outcomes of this research were
integrated in the original SNAME guidelines and are still influential on
the draft ISO (2009) code of practise. Since then, the geotechnical
offshore industry has continued to benefit from the centrifuge
methods, and both academic and industry users have developed a
Prototype
g
Model
rω
2
=ng
rω
Fig. 2. Inertial stresses in a centrifuge model induced by rotation about a fixed axis
correspond to the gravitational stresses in the corresponding prototype (after
Schofield, 1980).
σ
σ ρ
σ ρ
Fig. 3. Comparison of stress variation with depth in a centrifuge model and its
corresponding prototype (after Schofield, 1980).

strong expertise in analysing the centrifuge method outcomes,
incorporating them into the development of new design tools, and
developing deeper understanding in the offshore structure–soil
interaction. This is illustrated in Table 1 and in the following seven
examples.
3. Contributions of centrifuge methods to the spudcan
installation
On a modern jack-up, the maximum vertical leg load during
installation can exceed 140 MN and produce average vertical
bearing pressures on the spudcan in excess of 400 kPa. In soft
soils, this fully embeds the spudcan and can even cause penetration
of over 30 m. Recent centrifuge tests have helped characterise the
evolving mechanisms of the penetrating spudcan, as detailed in the
following three examples (and in Table 1).
3.1. Example 1: prediction of backflow and bearing capacity in
homogeneous clays
In model tests in clay at 1 g, the ratio of shear strength, su, to the
effective overburden stress, s0
v0, is higher than for an offshore
spudcan. However, producing correct stresses, due to soil self-
weight in experimental testing, is particularly important for the
continuous penetration of spudcans, where the soil flow mechan-
isms evolve with penetration depth and are affected by the strength
ratio, su/s0
v0. This is because the ratio directly controls the triggering
of soil to flow-around the footing from underneath to above
(defined as backflow). This ratio can be correctly simulated in
model tests in the centrifuge.
Spudcan penetration mechanisms were initially investigated in
the centrifuge by installing dry spaghetti markers vertically across
the centreline of the foundation in the undisturbed clay bed (Craig
and Chua, 1990, 1991), or by inserting lead threads through a soil
sample prior to testing (Murff, 1996). After completion of the test,
the soil sample was dissected along the centreline, permitting the
final deformation pattern to be observed. This only allowed the final
mechanism to be considered and did not provide information on the
ongoingmechanism changes, includingwhen thesoilbackflow occur-
red. Predictions of this were attempted by Springman and Schofield
(1998). In the centrifuge, they used a mini video camera fixed to the
model jack-up platform leg to capture the clay infill into the lattice leg.
Although this provided good images of the surface soil deformation,
mechanisms occurring within the soil could not be revealed.
By utilising new visualisation techniques for capturing soil
flow mechanisms in the centrifuge, Hossain et al. (2005) provided a
breakthrough in understanding the deep penetration mechanisms
of a spudcan into soft clay. The system, which combines digital still
photography, PIV and close range photogrammetry (GeoPIV, White
et al. (2003)), allows accurate resolution of the flow pattern around
a ‘half-object’ penetrated adjacent to a transparent window (neces-
sary due to the opacity of natural soils). The soil was confined within a
purpose designed strongbox with a plexiglass window to allow the
observation of the soil deformations, with the box mounted within
the drum centrifuge channel (see Fig. 2). Half-spudcan penetration
tests were conducted at an elevated gravity (50–200 g) tight against
the window of the strongbox. Images were captured continuously by
a high resolution digital still camera sitting at right angles on a cradle
within the channel. The experimental arrangement is shown in Fig. 4.
In the single layer clay, the soil flow patterns observed from
centrifuge model tests and continuous penetration finite element
analyses revealed three distinct mechanisms of soil flow-around
the advancing spudcan, as presented in Fig. 5 (Hossain et al., 2005,
2006). At a certain stage of penetration, soil backflow is initiated
and, in contrast to the recommendation in the current offshore
design guidelines (SNAME, 2008), Fig. 5 shows that this occurs not
because of instability of the open cavity1
, but because of a
preferential flow mechanism of soil from below the spudcan to
above it. A new design chart was proposed (see Fig. 6) along with a
robust formula to estimate the limiting cavity depth, H, above the
penetrating spudcan as
H
D
¼
suH
guD
0:55
À
1
4
suH
guD

ð1Þ
where D is the spudcan diameter, g0
is the submerged unit weight of
the clay and suH is the undrained shear strength at the backflow
depth, H. Eq. (1) has already replaced expressions that were based
on the hole collapse in offshore design guidelines (such as in the
draft ISO, 2009).
It is significant as it modifies the bearing capacity calculation of
a penetrating spudcan. Any soil backflow into the cavity created by
the spudcan penetration affects the bearing response in two ways:
(a) by (partially) negating the surcharge contribution, g0
d, and
(b) by increasing the shear resistance (and hence Nc) as the failure
mechanism now must pass through the backfilled soil. Since
backflow provides a seal over the top of the spudcan, the above
relationship also provides guidance on conditions, where transient
suctions may be sustainable beneath the spudcan, with a con-
sequential increase in uplift resistance and moment capacity at low
vertical loads. These were also shown to exist in centrifuge
experiments of deeply embedded spudcans by Cassidy et al.
(2004a), amongst others.
3.2. Example 2: installation in strong-over-soft soils
Jack-up installation and preloading in stratified deposits, where
a strong layer overlays weaker soil, has always been a challenge to
offshore engineers, due to the potential for catastrophic ‘punch-
through’ failure. Centrifuge testing has helped understand the
problem, as the higher stress, due to an enhanced soil self-weight at
elevated gravity has allowed researchers to more easily reconsti-
tute stratified soil deposits. In 1 g tests on the laboratory floor, it is
arduous to achieve bonding at the interface between two layers
Fig. 4. Set-up within the drum channel for a half-spudcan test (after Hossain and
Randolph (2010a)).
1
Offshore design guidelines, such as SNAME (1994, 2008), have suggested that
soil on top of a penetrating spudcan be assessed by evaluating the maximum stable
depth of an open cavity above the installing spudcan. This is based on the
investigations carried out by Meyerhof (1972), using Rankine’s pressure theory
and Britto and Kusakabe (1983) implementing the upper bound plasticity analysis.

with the layers often separating during testing. However, this can
be established more easily by simply testing under elevated gravity
(Hossain and Randolph, 2010a), or by allowing for significant con-
solidation prior to testing (Teh et al., 2008; Lee, 2009). Homo-
geneous sand layers can be laid through sand raining techni-
ques, including those developed for spraying sand in-flight (see Lee,
2009, for an example technique in a drum centrifuge). The develop-
ment of such capabilities has focused research onto understanding
spudcan punch-through mechanisms (Hossain and Randolph, 2010a;
Teh et al., 2010; Lee, 2009; Lee et al., 2009).
In stiff-over-soft clays, the failure mechanisms reported by Kim
(1978) from 1 g model tests on a surface circular footing are incon-
sistent compared to the recent centrifuge visualisation on penetrating
spudcan. Once again, half-spudcan penetration tests (at 100–200 g)
permitted the soil flow mechanisms to be captured with a digital
camera (Hossain and Randolph, 2010a). The experimental evidence
provided failure patterns at different spudcan penetration depths. The
quantified soil flow vectors showed that punch-through was asso-
ciated with the formation of distinct shear planes in the top layer (see
Fig. 7), and consequently a soil plug with the shape of an inverted
truncated cone was forced down into the underlying soft layer.
For a spudcan penetrating sand-over-clay, the situation is even
more complex. The spudcan behaviour in the sand layer is governed
by confining stress, qclay/qsand ratio and relative thickness of the
sand layer (t/D; where t is the thickness of the strong layer) and
they are a function of stress level and operative friction and dilation
angles. These vary with stress level and footing diameter, even on
sand layers with similar relative density (Lee et al., 2009). Revealing
this has taken centrifuge developments over a couple of decades.
Initially, Craig and Chua (1990, 1991) depicted post-test snapshots
of sand-over-clay punch-through behaviour through use of spa-
ghetti in the sample. Following this Okamura et al. (1997) reported
mechanisms for surface flat footings by employing a radiography
technique. More recently and again employing the image-based
analysis technique of half-spudcan penetration tests against a
transparent window, the detailed progressive failure mechanisms
at a sand-over-clay site were illustrated by Teh et al. (2008). The
mechanism at the time of punch-through is shown in Fig. 8. The key
finding is the dilatancy characteristics play a key role in the form of
the projected area beneath the advancing spudcan. They are supp-
ressed with the increase of t/D and the strength su of the lower
clay layer.
In order to develop a calculation method, the image results
discussed above require an augmentation with full load–
displacement profiles and numerical finite-element analysis. In
both stiff-over-soft clay and sand-over-clay sites, the load-pene-
tration response was also measured experimentally through full-
spudcan penetration tests. In the stiff-over-soft clay, centrifuge test
0.01
0.1
1
10
0.001 0.01 0.1 1 10
Normalised strength, suH/γγ′′′D
Normalisedcavitydepth,H/D
Typical design range
Centrifuge test
LDFE
γ′
−
γ′
=
s
4
1
D
s
D
H uH
Wall failure
Backflow
0.55
D
uH
Fig. 6. New design chart for estimating cavity depth after spudcan installation in
clay (after Hossain et al. (2006)).
Fig. 7. Spudcan punch-through on stiff-over-soft clay (from the PIV analysis: axes in
millimeters and in model scale) (after Hossain and Randolph (2010a)).
Fig. 5. Soil flow mechanisms of the spudcan penetration in the single layer clay: (a) heave mechanism, (b) backflow mechanism and (c) deep flow mechanism. Note that the
cavity depth corresponds to the depth, where the flow mechanism is initiated (after Hossain et al. (2006)).

data were also used to validate large deformation finite element
(LDFE) analyses, before undertaking the parametric analyses
(Hossain and Randolph, 2010b). The combination of half-spudcan
visual evidence, full spudcan load–displacement profiles and LDFE
results provided the basis for the development of a more rational
mechanism-based design approach reported by Hossain and
Randolph (2009). In the sand-over-clay, Lee et al. (2009) and Teh
et al. (2009) have reported new analytical design approaches
accounting for the failure patterns, the stress level and dilatant
response of the sand. All these approaches have seen evalua-
tion against field case studies in the recently completed InSafeJIP
(Osborne et al., 2008; 2009; InSafeJIP, 2009, 2010).
3.3. Example 3: reinstallation of jack-ups through existing seabed
footprints
The geotechnical centrifuge has provided insight into the problem
of jack-up spudcan reinstallation through an existing footprint in the
seabed. The issue is unique in offshore engineering and arises, because
jack-ups often return tothe same site foranadditionaldrillingwork or
for servicing a fixed platform. Locating a jack-up unit at a site, where
previous jack-up operations have occurred can be hazardous, because
of the spudcan footprints left on the seabed from the previous
operations. In soft clay soils, the footprints can be in an excess of
10 m deep and wide, with varying strength distributions from the
new surface to a depth below the original spudcan penetration
(Stewart and Finnie, 2001; Gan, 2010). Fig. 9 shows a typical scenario
of spudcan installation near an existing footprint.
The behaviour of spudcans during jack-up reinstallation is com-
plex, with the response dependent on the footprint geometry,
changing soil properties and the structural configuration and orienta-
tion of the jack-up unit itself. Centrifuge tests have confirmed that
preloading close to these footprints can result in eccentric and incli-
ned loading conditions (Stewart and Finnie, 2001; Cassidy et al., 2009;
Gan, 2010; Kong et al., 2010) and increased vertical penetration
through softer remoulded soils (Stewart and Finnie, 2001; Cassidy
et al., 2009; Gan, 2010; Kong et al., 2010). By using a free horizontal
slider as a connection piece in the experiment (Fig. 10), slewing of
the jack-up legs as the spudcan slides into the footprint was also
demonstrated (Gaudin et al., 2007). By quantifying these effects for
likely offshore scenarios, centrifuge tests have provided guidance to
the industry on the worst offset distance ratio (defined as the distance
between the centre of the spudcan and the centre of the footprint,
divided by the diameter of the spudcan) between installations.
This was demonstrated to be between 0.5 and 0.75 for lightly over-
consolidated clays. Beyond an offset ratio of 1.5, the footprint has no
significant effects on the spudcan penetration (Stewart and Finnie,
2001; Gaudin et al., 2007; Cassidy et al., 2009). These findings are
discussed in the new ISO site-assessment guidelines (ISO, 2009).
The shorter drainage paths and consolidation times have made
the centrifuge a particularly effective experimental method for this
problem. This is because the soil properties under the footprint vary
with the preload level, duration of preload hold and the duration of
time between the installation creating the spudcan and the reins-
tallation. The operational time a jack-up spends at one location can
be a number of years. However, centrifuge testing allows the equi-
valent dissipation of pore-pressures and change of soil strengths
Fig. 8. Observed mechanism of spudcan punch-through in sand-over-clay soils
(from the PIV analysis: axes in millimeters and in the model scale) (after Teh et al.
(2008)).
original spudcan
location
reinstalled location
remoulded and
reconsolidated soil
less soil
disturbance
new sea-bed
surface
Fig. 9. Typical spudcan reinstallation scenario.
Fig. 10. Sliding testing device used in the spudcan installation tests (setup in the
UWA drum centrifuge, after Gaudin et al. (2007)).

within the footprint in a matter of hours. Leung et al. (2007), Gan
et al. (2008) and Gan (2010) have effectively used the centrifuge to
study the change in soil properties of footprints, for both normally
consolidated and over-consolidated soils, reporting contours of
strength loss and gain. These new profiles of shear strength critically
affect the behaviour of the spudcan on reinstallation, as the shear
strength is now varying in both the vertical and horizontal directions.
4. Contributions of centrifuge methods to jack-up operations
Assessment of the operational phase of jack-up deployment
requires analytical models that can predict the ultimate load capa-
city and the corresponding displacements. For structures such as
jack-ups, the behaviour of the individual footings significantly influ-
ences the overall system response. The foundation behaviour is further
load-path dependent. Therefore, accurate modelling of the non-linear
load–displacement relationship of the spudcans is crucial to the pre-
diction of the global structural response, under working loads as well
as at an ultimate capacity. The use of centrifuge technology in the
development of single footing analytical models and their verification
in the structural push-over analysis of three-legged jack-ups is descri-
bed in the following examples 4 and 5, respectively.
4.1. Example 4: development of force-resultant models for combined
loading
The development of analytical models is ideally based on
parametric studies performed under carefully controlled condi-
tions. Results obtained from experiments carried out on small scale
physical models form the majority of the database used in the
development of force-resultant footing models (Martin and
Houlsby, 2001; Houlsby and Cassidy, 2002; Houlsby, 2003;
Cassidy et al., 2004b; Bienen et al., 2006). Force-resultant models
express the footing–soil interaction directly as the non-linear load–
displacement relationship at a reference point on the footing.
Typically, these have been written in a plasticity framework. Model
laboratory tests at 1 g have validated this approach and provided
the data to calibrate these force-resultant models (see Gottardi
et al., 1999; Martin and Houlsby, 2000; Byrne, 2000; Bienen et al.,
2006). Further calibration was undertaken using centrifuge techniques,
which allows stress similitude to the prototype to be maintained. Thus,
single footing tests in the centrifuge (e.g. Tan, 1990; Murff et al., 1992;
Cassidy et al., 2004a; Cassidy, 2007; Bienen et al., 2007) have allowed
additional model validation and calibration of the parameters under
conditionsrelevanttotheprototypeinwhatareregardedcurrentstate-
of-the-art force-resultant footing models. Fig. 11 shows an example of
a yield surface of a circular footing on loose silica sand established
using the swipe testing technique (Tan (1990), with underlying
assumptions further discussed in Gottardi et al. (1999)) in the
centrifuge, with the vertical load V normalised by the past largest
vertical load V0 plotted against the normalised resultant non-vertical
load Q. The experimental curves represent results of two different
ratios of applied horizontal displacement to rotation.
This work is significant as it also forms the experimental basis
for the yield surface approach used in the SNAME (1994, 2008) and
ISO (2009) guidelines. Interestingly, it was the jack-up industry
that first embraced the use of interaction surfaces written directly
in terms of the combined loads on the footing.
For conditions tested, the force-resultant model components do
not see major variation with soil type (Cassidy et al., 2002a, 2004a;
Byrne and Houlsby, 2001; Bienen et al., 2007; Cassidy, 2007;
Govoni et al., 2010). Some differences in the observed behaviour are
reported for the centrifuge results compared to the experimental
results obtained at 1 g. These include the shape and size of the yield
surface as well as the degree of association during yield (Bienen
et al., 2007). Further testing of the tensile behaviour of spudcans in
soft clay soils is required.
4.2. Example 5: centrifuge testing of three-legged jack-up response in
the centrifuge
Validation of the force-resultant models for load paths represen-
tative of field jack-up spudcans was still required as the load paths in
the single footing experiments were designed to establish the model
components (e.g. yield surface shape and size) and were not necessa-
rily representative of those followed by spudcans in the field.
Although comparison of the predicted response against field
data (e.g. Stock et al., 2000; HSE, 2001; Nelson et al., 2001; Cassidy
et al., 2002b; Nataraja et al., 2004) allows critical assessment of the
appropriateness and performance of analytical models, validation
up to the ultimate failure loads is not possible as no recorded sets
of field data are known to the authors, where a real jack-up was
loaded to failure. Challenges exist even for monitored conditions
before collapse. For instance, the relevant environmental loading
conditions in the field are not always known in full, adding uncer-
tainty in any retrospective analysis. Additional obstacles in validating
analytical models against field data include comprehensiveness and
quality as well as confidentiality of the measured data.
Compared to this, testing conditions in the centrifuge can be
carefully controlled, resulting in minimal uncertainty, and a scaled
jack-up can be pushed to toppling or sliding failure. Scaled models
of multi-legged jack-ups have therefore proved a useful comple-
ment to single footing tests and monitored offshore rigs in the
validation of numerical model performance.
In the 1990s, a large number of centrifuge experiments on model
jack-ups at Cambridge University boosted understanding of the geo-
technical aspects of the rigs’ behaviour. These experiments were per-
formed on clay (Dean et al., 1996, 1998) as well as sand (Murff et al.,
1991; Tsukamoto, 1994; Dean et al., 1995; Hsu, 1998), with rig install-
ation and preloading performed at stress levels relevant to the field
(i.e. at an enhanced gravity, thus ensuring similitude of the bearing
response of the model to the prototype). Horizontal load was applied
at the hull. The studies focussed on footing stiffness (rotational stiff-
ness in particular). While the initial tests on sand (Murff et al., 1991;
Tsukamoto, 1994) investigated drained behaviour, the later experi-
mental series (Dean et al., 1995; Hsu, 1998) was performed on satu-
rated sand and included monitoring of pore-pressure generation and
dissipation. Stiffness levels that were recorded during these experi-
ments formed the basis of the formulations used in the initial drafts of
the SNAME recommended practise document.
Other valuable insights were obtained from the centrifuge
experiments. Observations included the different load paths of
Fig. 11. Yield surface as established from the single footing experiments in the
centrifuge (after Cassidy (2007)).

the footings, decreasing footing stiffness with an increasing lateral
load, and non-linear hysteretic response in cyclic tests (example
results of cyclic centrifuge tests on footings with and without skirts
are shown in Fig. 12). In monotonic push-over tests, the two critical
conditions of lift-off or sliding of a spudcan were identified.
In all of the above tests, the horizontal load was applied along the
jack-up’s ‘axis of symmetry’, thus considering planar vertical, hor-
izontal, moment (VHM) loading only. As three-dimensional jack-ups
can be loaded from multiple directions in the field, further research
was undertaken at the University of Western Australia (UWA).
Amodeljack-up rigand associated loading apparatus(Fig. 13)were
developed for testing at 200 g in the UWA beam centrifuge (Bienen
et al., 2009a). As the aim of the investigation was to study the overall
response of the jack-up rigs to push-over loading, monotonically
increasing loads were applied at the hull. The centrifuge experiments
allowed for instrumentation that measured the jack-up’s displace-
ments and rotations in all six degrees-of-freedom in space (see Fig. 13)
as well as the load components on each of the three legs. For the first
time, experiments were performed of a jack-up loaded at various
angles, not only along the ‘axis of symmetry’. The continuously recor-
ded data allowed not only the measured ultimate load to be compared
to predictions, but the entire non-linear load–displacement response
up until failure. Because each leg was monitored, the detailed instru-
mentationenabledanalysisoftheoverallsystem,aswellasthechanges
and redistributions of loads between the spudcans.
Fig. 14 shows the global jack-up response measured in two
centrifuge experiments with different loading angles as an exam-
ple. The results are also compared in the figure to the predicted
response using structural finite elements and spudcan force-
resultant models (see example 4, and Bienen and Cassidy, 2009).
The results are shown for the hull reference point (HRP), which
coincides with the hull’s centre of gravity. While the resultant
horizontal hull displacement is similar in magnitude (though not in
direction), the different loading angles translate to different foot-
ing load paths. This affects the footing response and ultimately
the failure mode of the system. Failure is predicted numerically as
the vertical and moment load capacities tend to zero on the rear
footing(s) in response to the applied overturning load. The good
agreement of the measured and predicted responses highlights the
quality of prediction of the numerical force-resultant footing model.
The centrifuge tests of the scaled three-legged jack-up have therefore
Fig. 12. (a and b) Spudcan load paths during cyclic centrifuge experiments (Dean et al., 1995, 1998).
Strain gauges
Strain gauges
Pulley (pull-over
load application)
Application
of preloadDisplacement
sensor
Leg A
Leg C
Leg B
Fig. 13. Model jack-up for testing in the centrifuge (after Bienen (2009)).

added much confidence to the use of these force-resultant models for
offshore conditions (as recommended in a ‘‘Step 3’’ analysis in the
SNAME or ISO documents).
5. Contributions of centrifuge methods to the spudcan
extraction
Spudcan extraction often proves difficult and time-consuming in
the field, especially in soft soils, where deep penetrations are ex-
perienced. As no guidelines are currently available for the spudcan
extraction, various strategies to free the leg are usually employed
through a trial and error process (InSafeJIP, 2009). Therefore, the key
contributing factors to a successful extraction have remained uncertain
to the jack-up industry. Aspects that increase the level of complexity in
understanding spudcan extraction in the field include highly stratified
soil conditions, difficulties in quantifying the changes in soil strength
due to disturbance and reconsolidation, sometimes unquantifiable
wave excitations, as well as difficulties in measuring the loading
exerted during the extraction process on the jack-up. In order to
develop sound predictive methods for the expected resistance and to
devise successful extraction procedures, the governing soil failure
mechanisms must first be established.
As detailed in the following examples 6 and 7, centrifuge modell-
ing has recently provided an evidence of these extraction mechanisms
and analytical models have been developed based on these results.
5.1. Example 6: failure mechanisms and resistance components
during the spudcan extraction
As was shown in examples 1 and 3, soil failure mechanisms can be
visualised by testing half models against a transparent window in
combination with PIV and photogrammetry. Purwana et al. (2006,
2008, 2009) employed this technique to gain insight into soil failure
mechanisms during the spudcan extraction, an example of which is
shown in Fig. 15. In the left half of the figure, the photo taken during the
extraction test is presented, showing the spudcan and the clay to which
the coloured flock was added to allow for better visualisation of the soil
movement. The right half of the figure depicts the corresponding
vectors of soil displacement as obtained from the PIV analysis. The
results have proven valuable in determining the soil displacement
pattern and understanding the mobilisation of soil resistance during
the spudcan extraction. Importantly, the effect on extraction of soil
remoulding and consolidation during installation, preloading and
holding of self-weight during operation could all be modelled in a
timely manner in the centrifuge.
The centrifuge data can also be used as a basis for the develop-
ment of predictive methods. Such a model for the spudcan extraction
resistance was proposed by Purwana et al. (2009). It was developed
based on centrifuge extraction data from the spudcan embedments of
up to1.5diameters, and utilised experimentalrecordingsofresistance
at both the spudcan top and base, as well as pore-pressures. A similar
formulation for calculating the extraction resistance was adopted in
the InSafeJIP (2010) guidelines, also calibrated against centrifuge data.
5.2. Example 7: extraction with water jetting
Especially when an insufficient uplift load is available through
the jack-up hull buoyancy, water jetting may ease the spudcan
extraction. Jetting with nozzles located at the spudcan top face
aims at reducing resistance to an extraction through fracturing and
remoulding the soil. Jetting with nozzles at the spudcan invert
(i.e. the base of the spudcan), on the other hand, aims at decreasing
the negative pore-pressures mobilised by the uplifting spudcan.
This can extend to creating positive excess pore-pressures at the
spudcan invert, applying an additional active uplift force.
0.0
5.0
10.0
15.0
20.0
25.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Resultant horizontal displacement at the HRP [m]
Appliedload[MN]
Exp., Test 1
Exp., Test 2
Num., Test 1
Num., Test 2
Failure load Test 1 (22.0 MN)
Max. applied load Test 2 (17.9 MN)
Fig. 14. Measured and predicted global jack-up response (after Bienen and Cassidy (2009)).
Fig. 15. Visualisation of soil failure mechanism during spudcan extraction (after
Purwana et al. (2008)).

Insight into this has been provided by a series of centrifuge tests,
investigating various parameters including the extraction rate, the
jetting flow rate and the jetting pressure (Bienen et al., 2009b;
Gaudin et al., 2010a). A model spudcan with the ability to jet water
at different flow rates during a centrifuge test was used, as shown in
Fig. 16. The model represents 17.11 m diameter spudcan, currently
being used offshore. The spudcan invert featured three concentric
circles of twelve jetting nozzles each. Only one nozzle ring was used
at a time, the other two were blocked. The prototype spudcan
jetting nozzles are 38 mm in diameter. As direct scaling of the
nozzle diameter for testing at 200 g was technically not feasible,
the model jetting nozzles were 2 mm in diameter initially. This was
reduced to 0.5 mm after the first testing series. Dimensional
analysis, as developed in Gaudin et al. (2010a), was used to
determine the prototype flow rate according to the model pump
flow rate. A semicircular outlet guard above each nozzle redirected
the jetting flow along the bottom face of the spudcan, which is
consistent with an offshore practise.
Results demonstrated that the jetting efficiency relates to the ratio
of the jetting volume flow to the volume of the void theoretically
created at the invert, due to uplift of the spudcan (defined as the filling
ratio). The experimental data suggest an optimum jetting performance
not to coincide with vented extraction (i.e. a filling ratio of 1), but to a
mechanism where localised flow-around the spudcan edge still occurs
in addition to the uplift mechanism of the soil above the spudcan
(Bienen et al., 2009b; Gaudin et al., 2010a). The jetting flow appears to
be adominant factoroverthe jetting pressure, incontrast tothe general
belief.
From the understanding of mechanism gained from the cen-
trifuge tests, a conceptual framework for spudcan extraction with
water jetting was established based on (i) the pullout force
resulting from the buoyancy of the jack-up hull and (ii) the filling
ratio f. A relationship between the ratio of an applied extraction
force (Qdirect) to the expected extraction resistance without jetting
(Qult) and the filling ratio f was developed (Bienen et al., 2009b;
Gaudin et al., 2010a), which is shown in Fig. 17 (centrifuge test
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Filling ratio, f (-)
Fig. 17. Conceptualchartofjettingextractionefficiency.Thechartindicates,foragivenextractionload,therequiredflowrateforasuccessfuljettedextraction(afterGaudinetal.(2010a)).
Fig. 16. Model spudcan for extraction tests with water jetting (after Gaudin et al.
(2010a)). (a) spudcan base with jetting nozzles and deflectors and (b) water jetting in
model spudcan.

results are represented by the open circles). The filling ratio can be
related to the required parameter in the field, the jetting flow rate.
6. Future opportunities for application of the centrifuge
This paper has highlighted some of the advances made through
the use of centrifuge methods in understanding the jack-up
behaviour. With the jack-up industry moving to new areas with
more challenging soil conditions, further research is required.
There are significant opportunities for the centrifuge to contribute
to new understanding and to scientifically underpin the analysis
methods. The following opportunities have been identified:
Penetrometer correlation (installation prediction). The load-pene-
tration prediction of the spudcan installation usually uses
bearing capacity theory with soil strength parameters derived
from simple laboratory tests (usually performed offshore), and
occasionally cone penetrometer tests (CPTs). Correlation to
measured penetrometer resistance (accounting for the different
mechanisms taking place between cone and spudcan penetra-
tions) could represent an attractive alternative. There are chal-
lenges, however, in applying the centrifuge to this application.
Scaling of a penetrometer to in-situ conditions is not possible, with
for instance a 1 mm ball penetrometer required at say 100 g.
Recent developments using an epoxy to mould axial strain gauges
into the shaft of ball penetrometers have produced measurement
instruments with diameter as low as 4 mm (Lee, 2009), as shown
in Fig. 18. With careful account of the strain rate generated by the
penetration and of the difference in geometric scale, relative to the
different soil layers, it is possible to develop relevant correlations
from the centrifuge tests. A preliminary application of centrifuge
penetrometer data to the jack-up installation field cases offshore
Australia is discussed in Erbrich (2005).
Installation through footprints or sloped seabeds: predictive
methods and mitigation techniques are still required by an
industry for the installation of jack-ups through footprints or a
sloped seabed, to answer concerns related to collision with
adjacent fixed platforms or the possibility of structural damage
to the rig itself. Though the centrifuge has provided data on the
induced loads and displacements for a single footing, little work
has been performed to understand possible differences due to
the structural stiffness and movements of an installing three-
legged jack-up. Accounting for this soil-structural interaction
and for different installation scenarios is a future challenge,
which will require the development of innovative centrifuge
modelling techniques.
More realistic soil samples: drainage conditions, soils stratigra-
phy and soil sensitivity are important features to model to
improve the understanding of spudcan–soil interaction and to
be able to use centrifuge modelling for site specific studies. The
soil response to the spudcan loading is typically assumed in the
jack-up site-specific assessment guidelines to be either drained
when the coarse soil is considered, or undrained, when the fine-
grained soil is considered. For relatively permeable soil, such
as carbonate silt common offshore Australia, or silty sand with a
low permeability, the response may be partially drained, resul-
ting in an undrained bearing capacity factors underestimating
penetration or extraction resistance. Similarly, reconstitution of
soil stratigraphy and modelling soil’s sensitivity is critical to the
investigation of punch-through phenomenon and the assess-
ment of extraction resistance, respectively. These problems will
benefit from recent advances in soil reconstituting techniq-
ues using natural soil sampled from the site and ensuring that
key characteristics of the soil are correctly replicated (see for
instance Gaudin et al. (2010b)). These also rely on an extensive
in-situ characterisation so key parameters such as void ratio,
overconsolidation ratio, coefficients of compressibility and con-
solidation and in-situ strength can be used to design the sample
reconstitution process. Laying complex multi-layered stratigra-
phies within the centrifuge is also required.
Set-up effects: saturated soils consolidate under loading, with the
rate of consolidation depending on the coefficient of consolidation
of the soil and the length of the drainage path. Consolidation, even
if partial, can therefore lead to local strengthening (Young et al.,
1984; Barbosa-Cruz, 2007), also called the soil set-up. This may be
beneficial or have adverse effects (such as creating ‘‘artificial’’
punch-through potential after a delay during the jack-up installa-
tion process). Either case, however, requires improved under-
standing, which can be gained from an enhanced instrumentation
of centrifuge models, notably capturing the generation and
dissipation of excess pore pressure at the model surface. These
techniques, already used successfully for model suction caissons
(Chen and Randolph, 2007), are currently being transferred to the
model spudcans.
Cyclic loading: jack-up rigs are employed in the ocean environ-
ment, and therefore placed in locations, where cyclic loading is
an important consideration. The current state-of-the-art footing
models cannot account for the hysteresis and stiffness degrada-
tion associated with cyclic loading (though recommendations
on how to account for cyclic degradation within the yield surface
approach have been made by Dean and Metters (2009), amongst
others). Recent advances in motion control systems for centrifuge
models (such as described by De Catania et al. (2010)) will allow
Fig. 18. Miniature ball penetrometer with 4 mm diameter ball and 2 mm diameter shaft (after Lee (2009)). (a) Aligning stain gauges in epoxy mould and (b) completed ball
penetrometer.

cyclic loading of an entire storm, or multiple storms over the life of
an installed jack-up, to be applied.
Spudcan extraction: while recent research has advanced our
understanding of spudcan extraction, more comprehensive under-
standingofthedevelopmentof effectivestressesaround aspudcan
is desirable, both for unaided extractions and for those using water
jetting. Evaluation of required jetting volumes (base jetting) or
pressures (top jetting) is expected to relate to the evolution of
effective stresses around the spudcan. Current methods for base
jetting are limited to a narrow set of boundary conditions and
require further validation for other situations. Furthermore, the
current knowledge is restricted to the failure mechanisms that
develop at a relatively narrow range of spudcan embedment in soft
clay. Furthermore, the effect of small amplitude wave loading and
resulting cyclic loading on the spudcan extraction is currently not
understood. The centrifuge technology required to investigate
these issues is available.
For all these opportunities, centrifuge methods will play a role in
both increasing understanding of the soil–structure interaction and
the development of thorough predictive methods. However, there
is also a need to calibrate any new procedures against offshore field
measurements, as an application of new predictive methods to
highly complex and stratified seabeds is always a challenge.
7. Conclusions
Centrifuge modelling techniques have played an integral role
in developing new design and assessment methods for jack-up
spudcan foundations, many of which have been incorporated into
industry guidelines. This paper provides a review of recent con-
tributions covering all three phases of the jack-up installation, in-
situ operations and jack-up extraction. Areas where the centrifuge
has directly influenced an industry practise, particularly in chan-
ging recommended SNAME and ISO procedures and the recent
introduction of the InSafeJIP guidelines, have been highlighted
throughout the paper.
As centrifuge technology itself develops, further opportunities
will be created for solving the emerging issues faced by the jack-up
industry, as they move into deeper water and more challenging
seabed conditions. Some of the opportunities for the near future
have been showcased in this paper, and include amongst others:
direct prediction of jack-up installations using penetrometer data,
installation through footprints and sloped seabeds, spudcan beha-
viour in multi-layered and intermediate silty soils and operational
procedures for jetted spudcan extraction.
The geotechnical centrifuge will continue to provide pivotal
insights into the spudcan behaviour, but should not be considered
a stand-alone tool. Analytical methods developed through centrifuge
data offer maximum benefit when considered together with numer-
ical methods and field data. The latter is increasingly being collected
offshore and will play a critical role in the calibration and validation of
centrifuge outcomes to the more complex field conditions.
Acknowledgements
The authors acknowledge the sponsorship of the COFS compo-
nents of research covered in this review, including from the Keppel
Offshore and Marine, Woodside Energy Limited and the Australian
Research Council. The second author is the grateful recipient of an
Australian Research Council Future Fellowship. The authors acknowl-
edge and thank the anonymous reviewers, whose comments and
suggestions significantly enhanced the content of the paper.
References
Barbosa-Cruz, E.R., 2007. Partial consolidation and breakthrough of shallow
foundations in soft soil. Ph.D. Thesis, The University of Western Australia.
Bienen, B., 2009. Predicting the load–displacement response of a mobile jack-up
drilling rig on sand. Australian Geomechanics 44 (4), 1–12.
Bienen, B., Byrne, B., Houlsby, G.T., Cassidy, M.J., 2006. Investigating six degree-
of-freedom loading of shallow foundations on sand. Geótechnique 56 (6),
367–379.
Bienen, B., Cassidy, M.J., 2009. Three-dimensional numerical analysis of centrifuge
experiments on a model jack-up drilling rig on sand. Canadian Geotechnical
Journal 46 (2), 208–224.
Bienen, B., Cassidy, M.J., Gaudin, C., 2009a. Physical modelling of the push-over
capacity of a jack-up structure on sand in a geotechnical centrifuge. Canadian
Geotechnical Journal 46 (2), 190–207.
Bienen, B., Gaudin, C., Cassidy, M.J., 2007. Centrifuge tests of shallow footing
behaviour on sand under combined vertical–torsional loading. International
Journal of Physical Modelling in Geotechnics 7 (2), 1–21.
Bienen, B., Gaudin, C., Cassidy, M.J., 2009b. The influence of pull-out load on the
efficiency of jetting during spudcan extraction. Applied Ocean Research 31 (3),
202–211.
Britto, A.M., Kusakabe, O., 1983. Stability of axisymmetric excavations in clays.
Journal of Geotechnical Engineering, ASCE 109 (5), 666–681.
Byrne, B.W., 2000. Investigations of suction caissons in dense sand. D.Phil. Thesis,
University of Oxford.
Byrne, B.W., Houlsby, G.T., 2001. Observations of footing behaviour on loose
carbonate sands. Geótechnique 51 (5), 463–466.
Cassidy, M.J., 2007. Experimental observations of the combined loading behaviour of
circular footings on loose silica sand. Geótechnique 57 (4), 397–401.
Cassidy, M.J., Byrne, B.W., Houlsby, G.T., 2002a. Modelling the behaviour of circular
footings under combined loading on loose carbonate sand. Geótechnique 52
(10), 705–712.
Cassidy, M.J., Byrne, B.W., Randolph, M.F., 2004a. A comparison of the combined load
behaviour of spudcan and caisson foundations on soft normally consolidated
clay. Geótechnique 54 (2), 91–106.
Cassidy, M.J., Houlsby, G.T., Hoyle, M., Marcom, M., 2002b. Determining appropriate
stiffness levels for spudcan foundations using jack-up case records. In:
Proceedings of the 21st International Conference on Offshore Mechanics and
Arctic Engineering (OMAE), Oslo, Norway, OMAE2002-28085.
Cassidy, M.J., Martin, C.M., Houlsby, G.T., 2004b. Development and application of
force resultant models describing jack-up foundation behaviour. Marine
Structures 17, 165–193.
Cassidy, M.J., Quah, C.K., Foo, K.S., 2009. Experimental investigation of the
reinstallation of spudcan footings close to existing footprints. Journal of
Geotechnical and Geoenvironmental Engineering, ASCE 135 (4), 474–486.
Chen, W., Randolph, M.F., 2007. Radial stress changes and axial capacity for suction
caissons in soft clay. Geótechnique 57 (6), 499–511.
Craig, W.H.,. 1984. Preface. In: Proceedings of the International Symposium
Application of Centrifuge Modelling to Geotechnical Design, Manchester, UK, 1.
Craig, W.H., Al-Saoudi, N.K.S., 1981. The behaviour of some model offshore
structures. In: Proceedings of the 10th International Conference on Soil
Mechanics and Foundation Engineering, Stockholm, Sweden, 2, 541–556.
Craig, W.H., Chua, K., 1990. Deep penetration of spudcan foundations on sand and
clay. Geótechnique 40 (4), 541–556.
Craig, W.H., Chua, K., 1991. Large displacement performance of jack-up spudcans. In:
Proceedings of the International Conference on Centrifuge ’91, Rotterdam,
Balkema, 139–144.
Dean, E.T.R., James, R.G., Schofield, A.N., Tan, F.S.C., Tsukamoto, Y., 1993. The bearing
capacity of conical footings on sand in relation to the behavior of spudcan
footings of jack-ups. In: Proceedings of the Wroth Memorial Symposium:
Predictive Soil Mechanics, Oxford, 230–253.
Dean, E.T.R., Hsu, Y., Schofield, A.N., Murff, J.D., Wong, P.C., 1995. Centrifuge
modelling of 3-leg jackups with non-skirted and skirted spudcans on partially
drained sand. Offshore Technology Conference (OTC), Houston, OTC 7839.
Dean, E.T.R., James, R.G., Schofield, A.N., Tsukamoto, Y., 1996. Drum centrifuge study
of three-leg jackup models on clay. CEUD/D-Soils/TR289.
Dean, E.T.R., James, R.G., Schofield, A.N., Tsukamoto, Y., 1998. Drum centrifuge study
of three-leg jack-up models on clay. Geótechnique 48 (6), 761–785.
Dean, E.T.R., Metters, R., 2009. Cyclic stiffness degradation in nonlinear jackup
dynamics. In: Proceedings of the Offshore Technology Conference, Houston, OTC
19998.
De Catania, S., Breen, J., Gaudin, C., White, D.J., 2010. Development of a multiple axis
actuator control system. In: Proceedings of the Seventh International Con-
ference on Physical Modelling in Geotechnics, vol. 1, Zurich, 325–330.
Erbrich, C.T., 2005. Australian frontiers—spudcans on the edge. In: Proceedings of
the International Symposium on Frontiers in Offshore Geotechnics (ISFOG),
Perth, 49–74.
Finnie, I.M.S., Randolph, M.F., 1994. Bearing response of shallow foundations in
uncemented calcareous soil. In: Proceedings of the International Conference on
Centrifuge ’94, Rotterdam, Balkema.
Gan, C.T., 2010. Centrifuge model study on spudcan-footprint interaction. Ph.D.
Thesis, National University of Singapore.
Gan, C.T., Cassidy, M.J., Gaudin, C., Leung, C.F., Chow, Y.K., 2008. Drum centrifuge
model tests on spudcan footprint characteristics in normally consolidated and

over-consolidated kaolin clay. Centre for Offshore Foundation System, Uni-
versity of Western Australia. Research report no. 08469.
Garnier, J., Gaudin, C., Springman, S.M., Culligan, P.J., Goodings, D., Konig, D., Kutter,
B., Phillips, R., Randolph, M.F., Thorel, L., 2007. Catalogue of scaling laws and
similitude questions in centrifuge modelling. International Journal of Physical
Modelling in Geotechnics 7 (3), 1–24.
Gaudin, C., Cassidy, M.J., Donovan, T., 2007. Spudcan reinstallation near existing
footprints. In: Proceedings of the Sixth International Conference of Offshore Site
Investigation and Geotechnics, 11–13 September, London, 285–292.
Gaudin, C., Bienen, B., Cassidy, M.J., 2010a. Investigation of the potential of bottom water
jetting to ease spudcan extraction in soft clay. Geótechnique. Accepted 7 April 2010.
Gaudin, C., Cluckey, E.C., Garnier, J., Phillips, R., 2010b. New frontiers for centrifuge
modelling in offshore geotechnics. In: Proceedings of the Second International
Symposium on Frontiers in Offshore Geotechnics, Perth, Australia.
Gottardi, G., Houlsby, G.T., Butterfield, R., 1999. Plastic response of circular footings
on sand under general planar loading. Geótechnique 49 (4), 453–469.
Govoni, L., Gourvenec, S., Gottardi, G., 2010. Centrifuge modeling of circular shallow
footings on sand. International Journal of Physical Modelling in Geotechnics 10
(2), 35–46.
Hossain, M.S., Hu, Y., Randolph, M.F., White, D.J., 2005. Limiting cavity depth for
spudcan foundations penetrating clay. Geótechnique 55 (9), 679–690.
Hossain, M.S., Randolph, M.F., Hu, Y., White, D.J., 2006. Cavity stability and bearing
capacity of spudcan foundations on clay. In: Proceedings of the Offshore
Technology Conference, Houston, OTC 17770.
Hossain, M.S., Randolph, M.F., 2009. New mechanism-based design approach for
spudcan foundations on stiff-over-soft clay. In: Proceedings of the Offshore
Hossain, M.S., Randolph, M.F., 2010a. Deep-penetrating spudcan foundations on
layered clays: centrifuge tests. Geótechnique 60 (3), 157–170.
Hossain, M.S., Randolph, M.F., 2010b. Deep-penetrating spudcan foundations on
layered clays: numerical analysis. Geótechnique 60 (3), 171–184.
Houlsby, G.T., 2003. Modelling of shallow foundations for offshore structures. In:
International Conference on Foundations (ICOF), Dundee, Scotland, 11–26.
Houlsby, G.T., Cassidy, M.J., 2002. A plasticity model for the behaviour of footings on
sand under combined loading. Geótechnique 52 (2), 117–129.
HSE (Health and Safety Executive), 2001. Interpretation of full-scale monitoring data
from a jack-up rig. Offshore Technology Report 2001/035.
Hsu, Y.S., 1998. Excess pore pressure under cyclically loaded model jack-up
foundations. Ph.D. Thesis, Cambridge University.
InSafeJIP, 2009. Improved guidelines for the prediction of geotechnical performance
of spudcan foundations during installation and removal of jack-up units. First
year report. Authors: Osborne, J.J., Teh, K.L., Houlsby, G.T., Cassidy, M.J., Bienen,
B., Leung, C.F.
InSafeJIP, 2010. Improved guidelines for the prediction of geotechnical performance
of spudcan foundations during installation and removal of jack-up units.
Proposed Industry Guidelines. Authors: Osborne, J.J., Teh, K.L., Houlsby, G.T.,
Cassidy, M.J., Bienen, B., Leung, C.F.
ISO, 2009. Petroleum and natural gas industries – site-specific assessment of mobile
offshore units – part 1: jack-ups. International Organization for Standardization,
ISO 19905-1. Draft Release.
Kim, S.W., 1978. Bearing capacity of footings on two-layered clays under inclined
loads. M.Eng. Thesis, Nova Scotia Technical College.
Kong, V.W., Cassidy, M.J., Gaudin, C., 2010. Jack-up reinstallation near a footprint
cavity. In: Proceedings of the Seventh International Conference on Physical
Modelling in Geotechnics (ICPMG 2010). Zurich, vol. 2, 1033–1038.
Lee, F.H., 2001. The philosophy of modelling versus testing. In: Proceedings of the
International Symposium on Constitutive and Centrifuge Modelling; Two
extremes, Monte Verita, Switzerland, 113–131.
Lee, K.K., 2009. Investigation of potential punch-through failure on sands overlaying
clay soils. Ph.D. Thesis, The University of Western Australia.
Lee, K.K., Randolph, M.F., Cassidy, M.J., 2009. New simplified conceptual model for
spudcan foundations on sand overlying clay soils. In: Proceedings of the
Offshore Technology Conference, Houston, OTC-20012.
Le Tirant, P., 1979. Seabed reconnaissance and offshore soil mechanics for the
installation of petroleum structures. Technip, Paris.
Leung, C.F., Gan, C.T., Chow, Y.K., 2007. Shear strength changes within jack-up
spudcan footprint. In: Proceedings of the 17th International Offshore and Polar
Engineering Conference (ISOPE), Lisbon, Portugal, 1504–1509.
Leung, C.F., Xie, Y., Chow, Y.K., 2006. Centrifuge model study of spudcan-pile
interaction. In: Proceedings of the 16th International Offshore and Polar
Engineering Conference (ISOPE), San Francesco, 530–535.
Leung, C.F., Xie, Y., Chow, Y.K., 2008. Use of PIV to investigate spudcan–pile
interaction. In: Proceedings of the 18th International Offshore and Polar
Engineering Conference (ISOPE), Vancouver, 721–726.
Martin, C.M., 2001. Impact of centrifuge modelling on offshore foundation design.
In: Proceedings of the International Symposium on Constitutive and Centrifuge
Modelling; Two extremes, Monte Verita, Switzerland, 135–154.
Martin, C.M., Houlsby, G.T., 2000. Combined loading of spudcan foundations on clay:
laboratory tests. Geótechnique 50 (4), 325–338.
Martin, C.M., Houlsby, G.T., 2001. Combined loading of spudcan foundations on clay:
numerical modeling. Geótechnique 51 (8), 687–699.
Meyerhof, G.G., 1972. Stability of slurry trench cuts in saturated clay. In: Proceedings
of the Speciality Conference Performance of Earth and Earth Supported
Structures, Lafayette 1, Part 2, 1451–1466.
Muir Wood, D.M., 2004. Geotechnical Modelling. Spon Press, Taylor Francis.
Murff, J.D., 1996. The geotechnical centrifuge in offshore engineering. In: Proceed-
ings of the Offshore Technology Conference, OTC 8265.
Murff, J.D., Hamilton, J.M., Dean, E.T.R., James, R.G., Kusakabe, O., Schofield, A.N.,
1991. Centrifuge testing of foundation behaviour using full jack-up rig models.
Offshore Technology Conference (OTC), Houston, Texas, OTC 6516.
Murff, J.D., Prins, M.D., Dean, E.T.R., James, R.G., Schofield, A.N., 1992. Jackup rig
foundation modelling. Offshore Technology Conference, Houston, OTC 6807.
Nataraja, R., Hoyle, M.J.R., Nelson, K., Smith, N.P., 2004. Calibration of seabed fixity
and system damping from GSF Magellan full-scale measurements. Marine
Structures 17, 245–260.
Nelson, K., Stonor, R.W.P., Versavel, T., 2001. Measurements of seabed fixity and
dynamic behaviour of the Sants Fe Magellan jack-up. Marine Structures 14,
483–541.
Ng, T.G., Lee, F.H., 2002. Cyclic settlement behaviour of spudcan foundations.
Geótechnique 52 (7), 469–480.
Noble Denton Associates, 1987. Foundation Fixity of Jack-up Units: a Joint
Industry Study. Noble and Denton Associates.
Osborne, J.J., Teh, K.L., Leung, C.F., Cassidy, M.J., Houlsby, G.T., Chan, N., Devoy, D.,
Handidjaja, P., Wong, P., Foo, K.S., 2008. An introduction to the InSafe JIP. In:
Proceedings of the Second Jack-up Asia Conference, Singapore.
Osborne, J.J., Houlsby, G.T., Teh, K.L., Bienen, B., Cassidy, M.J., Randolph, M.F., Leung,
C.F., 2009. Improved guidelines for the prediction of geotechnical performance
of spudcan foundations during installation and removal of jack-up units. In:
Proceedings of the 41st Offshore Technology Conference, Houston, OTC 20291.
Okamura, M., Takemura, J., Kimura, T., 1997. Centrifuge model test on bearing
capacity and deformation of sand layer overlying clay. Soils and Foundations 37
(1), 73–88.
Purwana, O.A., Leung, C.F., Chow, Y.K., Foo, K.S., 2006. Breakout failure mechanism of
jackup spudcan extraction. In: Proceedings of the Sixth International Conference
of Physical Modelling in Geotechnics (ICPMG06), Hong-Kong, 1, 667–672.
Purwana, O.A., Quah, M., Foo, K.S., Leung, C.F., Chow, Y.K., 2008. Understanding
spudcan extraction problem and mitigation devices. In: Proceedings of the
Second Jack-Up Asia Conference Exhibition, Singapore.
Purwana, O.A., Quah, M., Foo, K.S., Nowak, S., Handidjaja, P., 2009. Leg extraction/
pullout resistance—theoretical and practical perspectives. In: Proceedings of
the 12th International Conference The Jack-Up Platform Design, Construction
Operation, London.
Randolph, M.F., 2004. Characterisation of soft sediments for offshore applications.
Keynote Lecture In: Proceedings of the Second International Conference on Site
Characterisation, Porto, 1, 209–231.
Rowe, P.W., Craig, W.H., 1981. Applications of models to the prediction of offshore
gravity platform foundation performance. In: Proceedings of the International
Conference on Offshore Site Investigation, London, 269–281.
Schofield, A.N., 1980. Cambridge geotechnical centrifuge operations. Geótechnique
30 (3), 227–268.
Siciliano, R.J., Hamilton, J.M., Murff, J.D., Phillips, R., 1990. Effect of jackup spudcans
on piles. Offshore Technology Conference, Houston, OTC 6467.
SNAME, 1994. Recommended Practice for Site Specific Assessment of Mobile Jack-up
Units. TR Bulletin 5-5A first ed. Society of Naval Architects and Marine
Engineers, New Jersey.
SNAME, 2008. Recommended practice for site specific assessment of mobile jack-up
units. TR Bulletin 5-5A, first ed.—Rev. 3, Society of Naval Architects and Marine
Engineers, New Jersey.
Springman, S.M., Schofield, A.N., 1998. Monotonic lateral load transfer from a jack-
up platform lattice leg to a soft clay deposit. In: Proceedings of the International
Conference on Centrifuge ’98, Rotterdam: Balkema, 563–568.
Stewart, D.P., Finnie, I.M.S., 2001. Spudcan-footprint interaction during jack-up
workovers. International Society of Offshore and Polar Engineers (ISOPE),
Cupertino, California 1, 61–65.
Stock, D.J., Lewis, D.R., Baucke, T.C., Hsu, H.Y., 2000. Hurricane Georges hindcast
assessment of LeTourneau 116-C and 82-SD-C jackups. Offshore Technology
Conference (OTC), Houston, OTC 12075.
Tan, F.S.C., 1990. Centrifuge and numerical modelling of conical footings on sand.
Ph.D. Thesis, University of Cambridge.
Taylor, R.N., 1995. Geotechnical Centrifuge Technology. Blackie Academic and
Professional.
Teh, K.L., Cassidy, M.J., Leung, C.F., Chow, Y.K., Randolph, M.F., Quah, C.K., 2008.
Revealing the bearing failure mechanisms of a penetrating spudcan through
sand overlaying clay. Geótechnique 58 (10), 793–804.
Teh, K.L., Cassidy, M.J., Chow, Y.K., Leung, C.F., 2006. Effects of scale and progressive
failure on spudcan ultimate bearing capacity in sand. In: Proceedings of the
International Symposium on Ultimate States of Geotechnical Structures, Marne-
la-Valee, France, 1, 481–489.
Teh, K.L., Leung, C.F., Chow, Y.K., Handidjaja, P., 2009. Prediction of punch-through
for spudcan penetration in sand overlying clay. In: Proceedings of the Offshore
Teh, K.L., Leung, C.F., Chow, Y.K., Cassidy, M.J., 2010. Centrifuge model study of
spudcan penetration in sand overlying clay. Geótechnique 60 (11), 825–842.
Tsukamoto, Y., 1994. Drum centrifuge tests of three-leg jack-ups on sand. Ph.D.
Thesis, Cambridge University.
White, D.J., Take, W.A., Bolton, M.D., 2003. Soil deformation measurement using
particle image velocimetry (PIV) and photogrammetry. Geótechnique 53 (7),
619–631.
White, D.J., Teh, K.L., Leung, C.F., Chow, Y.K., 2008. A comparison of the bearing
capacity of flat and conical circular foundations on sand. Geótechnique 58 (10),
781–792.

Wong, P.C., Chao, J.C., Murff, J.D., Dean, E.T.R., James, R.G., Schoﬁeld, A.N., Tsukamoto,
Y., 1993. Jack up rig foundation modelling II. Offshore Technology Conference
(OTC), Houston, OTC 7303.
Xie, Y., Leung, C.F., Chow, Y.K., 2006. Effects of spudcan penetration on adjacent piles.
In: Proceedings of the Sixth International Conference on Physical Modeling in
Geotechnics, Hong Kong, vol. 2, 701–706.
Xie, Y., Leung, C.F., Chow, Y.K., 2010. Study of soil movements around a penetrating
spudcan. In: Proceedings of the Seventh International Conference on Physical
Modeling in Geotechnics, Zurich, vol. 2, 1075–1080.
Young, A.G., Remmes, B.D., Meyer, B.J., 1984. Foundation performance of offshore
jack-up drilling rigs. Journal of GeotechnicalEngineering Division, ASCE 110 (7),
841–859.

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