Volume 3, Issue 1 March 2018

Special Contribution

Potential Damage to Steel Pipe Piles During Installation
Prof. Dr. M.F. Randolph
Fugro Chair in Geotechnics, Centre for Offshore Foundation Systems
The University of Western Australia

ABSTRACT
Steel pipe piles are widely used both onshore and offshore because of their good bending stiffness and ease of installation.
They are generally vibrated, driven or jacked open-ended, although internal plates or even complete end-closures may
be used to improve their bearing capacity. Large diameter, thin-walled open-ended piles are susceptible to distortion at
the tip, particularly when installed into stratified sediments where the soil conditions may vary spatially, both with depth
and within planes normal to the pile axis. A particular form of damage is extrusion buckling where progressive distortionof the pile occurs, starting from the tip, as it penetrates through the soil. Case histories illustrating this form of collapse
are shown and possible triggers for damage discussed.
1

INTRODUCTION

Piles are vulnerable to damage during jacking or driving into strong soils or weak rock. This may often go undetected,
with the only indication being a driving resistance that deviates from the expected profile. Figure 1 shows two contrasting
examples from onshore pile driving. In one case tip buckling of an H-pile has occurred due to encountering unweatheredbasalt at a shallower depth than anticipated; in the other case a thin-walled casing has become distorted during driving,possibly due to encountering a buried object within made ground.

(a) Tip buckling of H-pile(b) Distortion of thin-walled casing

Figure 1 Examples of damage during driving

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Volume 3, Issue 1 March 2018

A more general case of widespread damage inthe vicinity of the pile tip, which wentcompletely unnoticed during the original
installation, is shown in Figure 2 (Broos et al.
2017). The piles, which were extracted during
widening a harbour basin in Rotterdam, were1420 mm diameter with 17 mm wall thickness
in the region of the tip. They had been installedby driving at a rake of 1 in 5, bearing in medium
to dense sands with cone resistance of 25 to 40
MPa. It is quite likely that the raking angle(around 11 degrees) contributed to the
distortion, since the pile tip would haveencountered any stronger stratum at one edge.
The relatively large diameter to wall thickness
ratio (D/t) of 84 for the piles shown in Figure 2
may be viewed in the context of the current
trend in open-ended pile geometries, inparticular the very large diameter monopiles
now in use for European offshore windfarms.
A typical monopile is shown in Figure 3. Overmuch of the pile length the wall thickness may
be no more than 75 mm (D/t of 100), but withthicker sections in regions of high bending
moment (near the seabed surface) and at thepile tip where the pile is reinforced internallywith a driving shoe.
The concern for piles with large D/t ratios is
the potential for damage to occur duringtransportation and installation. Typically,
construction tolerances on ‘out of roundness’
are for maximum deviation from a true circleof ~0.5 % of the pile radius (DNV 2010). While
such tolerances may be verified immediately
prior to installation, heterogeneities within thesoil can trigger distortion. Indeed progressive
elliptical (and beyond) distortion of pipe pilesin the offshore environment, a process
referred to as ‘extrusion buckling’ has been
identified on several occasions, as indicated in
Figure 4. The API guideline shown forcomparison, and which is often used as thebasis for choosing the pile wall thickness at
the tip, targets a different form of tip damage,linked to generation of excessive axial stresses
during installation by driving. It is evident thatit does not provide safe guidance for gradual
distortion that occurs in extrusion buckling.

Figure 2 Evidence of extrusion buckling at the toe of tubular king piles
extracted from the port basin in Rotterdam

7.5 m diameter
65.5 m long
940 tonnes
installed July 2015

GroundEngineering,
August 2014

Figure 3 Photograph of 7.5 m diameter monopiles for the GodeWind farmFigure 4 Trends in open-ended pile geometries. Confirmed andsuspected extrusion buckling damage indicated by red and purple
circles respectively
4Volume 3, Issue 1 March 2018

2

CASE STUDIES

Two well-studied case studies of extrusion buckling are summarised briefly below.
2.1 Case study 1: Goodwyn A, North-West Shelf of Australia
The Goodwyn A platform was installed on the North-West Shelf of Australia in the late 1980s. The seabed comprised
relatively low strength calcareous silt and sand layers down to a depth of about 110 m, below which calcarenite wasfound. Given the low shaft capacity of driven piles in calcareous soils, the adopted foundation design consisted of primarypiles driven through the uncemented sediments, below which grouted insert piles were to provide the main axial support(Figure 5). The platform included 20 piles, 5 at each corner, with diameter 2.65 m and wall thickness 45 mm (D/t = 59).
However, when attempts were made to drill out the soil plug within the driven primary piles, to enable construction of
the grouted insert piles, it was found that 16 of the 20 piles had undergone progressive distortion to the extent that thepile tips had become almost closed into a peanut shape. The distortion started at about the depth of a layer of cemented
material (3 to 5 m thick, with cone resistance upwards of 60 MPa) embedded within the calcareous silt and sand layers(Figure 6).

132 m
water

primary
piles

groutedinsertpiles(a) View from the air(b) Elevation of platform and foundations

Figure 5 Overview of Goodwyn A platform on North-West Shelf of Australia

Hard layer←(b) Progressive pile
distortion below hard layer←(a) Profile ofcone resistance

Figure 6 Soil strength profile and measured growth in pile distortion5

Volume 3, Issue 1 March 2018

In order to understand the process of extrusion buckling, a numerical technique (BASIL) was developed within ABAQUS(Barbour & Erbrich 1995, Erbrich et al. 2010). The pile-soil interaction is represented by layers of ‘hair’ springs distributed
around (and along the length of) the embedded section of the pile (Figure 7a). The zero force and displacement for eachspring is taken from the point where the pile tip ‘cuts’ the hair spring. As the pile advances further, any forced radial
movement of the spring (for example, if the pile wall is not parallel to the direction of advance) will invoke a force acting
on the pile wall.
The analysis typically starts with the pile pre-embedded to some depth, and with the pile tip distorted according to theshape of a radial buckle (mode 1), with the maximum out of roundness adjusted in a parametric fashion, but typically 0.5
to 2 % of the pile radius. The pile is then advanced through the sets of soil springs, each of which has been pre-assigned
an appropriate non-linear load-displacement response curve.
An example outcome from a BASIL simulation of extrusion buckling of a Goodwyn A pile is shown in Figure 8 (see also
Erbrich et al. 2010). In order to achieve the progressive distortion, an initial out of roundness of 25 mm (1.9 % of the pile
radius) was needed, which is somewhat outside the specified tolerance (Figure 7b). Notwithstanding potential limitationsof the numerical analysis, the need to apply a more significant initial distortion indicates that some external factor might
have contributed to initial damage of the pile tip prior to installation, either a structural collision during stabbing of thepile or lateral heterogeneity of the cemented sediment layer.
At the time of the Goodwyn A platform installation, the pile D/t ratio of 59 was somewhat greater than in routine practicein the offshore oil and gas industry. However, as discussed above, many of the very large diameter monopiles used in theoffshore wind industry have adopted much higher D/t ratios.

(a) Soil represented as ‘hair’ springs78(b) Initial imperfection (exaggerated)

Figure 7 Numerical modelling approach to investigate extrusion buckling

Yielded
Zone

60 m
70 m

80 m

Hard layer

90 m

100 m penetration

Figure 8 Example pattern of plastic strains for a pile pushed 25 m beyond the hard layer
6Volume 3, Issue 1 March 2018

2.2 Case study 2: Valhall, North Sea
The Valhall water injection platform was installed in the North Sea in 2002, but encountered problems when 5 of the 8piles reached refusal at penetrations between 45 and 55 m, compared with the target penetration of around 70 m (Almet al. 2004). The premature refusal meant that external weld beads, and the profiled variations in pile wall thickness,were then not at their anticipated design depths relative to the jacket structure. Investigations revealed that the piles
that met refusal had undergone extrusion buckling to the extent that the tips were almost closed (Figure 9). The soil
stratigraphy below about 37 m comprised very dense sands, with cone resistances estimated as about 80 MPa. The piles
were 2.44 m in diameter, with a wall thickness of 60 mm (so D/t of 40), hence consistent with routine practice.
During investigations into the cause of the pile distortion, attention focused on what might seem a relatively minor design
detail, in the form of an external chamfer that was applied to the pile tips (Figure 10). In the context of the 2.44 m pile
diameter, it is perhaps surprising that this detail could have such ramifications for pile installation. However, analysis
suggests that the chamfer may indeed give rise to significantly greater external radial stresses acting on the pile wall,hence triggering distortion.
Cone resistance qc (MPa)
0
50
100
0
5
10

Depth (m)

15

20
25

Clay; su = 400 kPa

30
35

Clay; su = 400 kPa

40
45
50

(b) Typical distortion of lower part of pile(a) Simplified cone profile

Figure 9 Soil profile and surveyed pile distortion for Valhall
Chamfered pile tip
60 mm

120 mm14
30
30 mm

2.438 mmFigure 10 Detail of chamfered pile tip
7Volume 3, Issue 1 March 2018

Analyses using BASIL were carried out to explore conditions for triggering extrusion buckling, allowing for the radial stressenhancement of the chamfered tip. Figure 11 (Erbrich, private communication) shows example output for an initial outof roundness of 0.8 % of the pile radius. The pile was pre-embedded to 10 m and then pushed to a penetration of 50 m.
Although full collapse was not achieved, significant outward (in one plane) and inward (in a perpendicular plane)
movements occurred, hence initiating extrusion buckling.
Pile radius (m)
1.05
10

Depth
(m)

1.1

1.15

1.2

1.25

1.3

Initialradius20
Pile tiprecovers
in clay

30

40
Pile tip
moves in
120 mmPile tip movesout 95 mm
50

Figure 11 Soil profile and surveyed pile distortion for Valhall
3

INITIATION AND PROPAGATION OF EXTRUSION BUCKLING

Extrusion buckling can be initiated during driving of pipe piles by a variety of conditions that include:(1) initial out of roundness of the pile cross-section with non-verticality of the pile wall;(2) high differential internal and external stresses acting on the pile wall from the soil;(3) heterogeneous soil conditions.
In each case, it is necessary for the soil to be sufficiently stiff to overcome the elastic hoop stiffness of the steel, and also
– in the case of (2) and (3) – to generate differential radial stresses of sufficient magnitude. Conditions (1) and (2) areconsidered the most likely primary causes of the pile distortion discussed above in case studies 1 and 2. Clearly any plastic
distortion of the circularity of the pile section near the tip would be expected to propagate further during driving throughstrong soils. Equally, if the differential
stresses across the pile wall exceed theradial buckling pressure (the Bressepressure, HSE 2001), then potential
instability of the pile circularity can beinitiated.
Q
Localised
The effect of heterogeneous soil conditions
high soil
is illustrated in Figure 12. An eccentric zonepressureof stronger soil, a layer dipping relative tothe horizontal, or a raking pile encountering
Counteracting
Ring stiffness
a stronger horizontal layer, will tend tosoil pressuresinversely
proportional
Sloping
apply localised pressure in one region of
to
cube
of
D/t ratio
sand layer
the cross-section. For high D/t ratios the
Pile
tip
will
hoop stiffness of the pile is significantly
tend to distort
lower than the corresponding soil stiffness,hence the soil will distort the pile rather
than the other way round.
Figure 12 Initiation of pile tip distortion in heterogeneous soil

8Volume 3, Issue 1 March 2018

The hoop stiffness and critical radial buckling pressure are given by

Hoop stiffnes (Figure 12):
Critical Bresse pressure:Q
10~
E steel  D / t 3

(1)

pe
2

Esteel  D / t 3

Both quantities are inversely proportional to the cube of the diameter to wall thickness ratio (D/t). Thus, for a D/t ratioof 80, the hoop stiffness and critical Bresse pressures would be about 4 MPa and 0.8 MPa respectively. The latter figure
is of the same order of magnitude as the external radial stresses expected in relatively uniform layers of dense sand withcone resistance in excess of 50 MPa, but the low hoop stiffness is the more critical factor in initiation of pile tip distortion.
The hoop stiffness may be compared with the initial gradient of a load transfer curve for lateral pile response. This would
exceed the pile hoop stiffness for soil with shear modulus greater than about 1 MPa – so easily satisfied in all but quite
soft soils. This is consistent with a similar assessment, although for somewhat thicker walled piles, by Aldridge et al.
(2005).
For heterogeneous or dipping soil layers such as shown in Figure 12, localized increased soil stresses across the relevant
vertical plane will initiate distortion of the pile tip, provided the soil stiffness is sufficiently high. Extrusion buckling is thenlikely to proceed, since minor distortion exacerbates the increased external stresses in that plane, while increased internal
stresses will be generated across the perpendicular plane. The process is illustrated in Figure 13, considering a situation
where the originally circular pile section has been distorted into an elliptical shape. If the pile wall at any given location
around the tip attempts to advance vertically (parallel to the pile axis) as the pile penetrates further, the external stresses
will be increased further across the minor axis of the ellipse, while the internal stresses will be increased across the major
axis of the ellipse. This provides a feedback loop, which will instead encourage the pile wall to advance parallel to its
current direction in each vertical plane (see dashed arrows in Figure 13).

direction ofpenetration

s′3
s′1

s′1
s′3

excess externalpressure

excess internalpressure

Figure 13 Schematic of extrusion buckling kinematics

9Volume 3, Issue 1 March 2018

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CONCLUSIONSThe offshore oil and gas and renewable energy industries have provided incentive towards ever increasing diameters of
open-ended steel piles to support jacket structures and offshore wind turbines. Fabrication techniques have developedin parallel, now enabling piles with diameters of 8 m or more to be constructed to tight tolerances. However, one aspectthat has received less attention than it deserves is the construction risk associated with installing large diameter piles
with very high ratios of diameter to wall thickness.
This paper has provided some background information illustrating a process of gradual tip distortion referred to as
extrusion buckling. Although the process may be simulated using numerical analysis, this is more commonly undertaken
retrospectively, after a problem has arisen, rather than during the design phase. The mechanism is well understood, but
the analysis is relatively complex and at present there are only very limited guidelines to guard against situations where
extrusion buckling may occur.
REFERENCES
Aldridge, T.R. Carrington, T.M. & Kee, N.R. 2005. Propagation of pile tip damage during installation. Proc. ofInternational Symposium on Offshore Geotechnics, Perth, Taylor & Francis, 823-827.
Alm, T., Snell, R.O., Hampson, K.M. & Olaussen, A. 2004. Design and installation of the Valhall piggyback structures.
Proc. of Offshore Technology Conference, Houston, Paper OTC 16294.
API. 2011. Recommended Practice 2GEO Geotechnical and Foundation Design Considerations, 1st Edition,
American Petroleum Institute, Washington.
Barbour, R. & Erbrich, C.T. 1995. Analysis of soil skirt interaction during installation of bucket foundations using ABAQUS.
Proc. Of ABAQUS Users Conference, Paris.
Broos, E., Sibbes, R. & de Gijt J. (2017). Widening a harbor basin, demolition of a deep see quay wall in Rotterdam.
Proc. of COME2017: Decommissioning of Offshore Geotechnical Structures, Hamburg, Germany, 251-262.
DNV 2010. Fabrication and Testing of Offshore Structures, Offshore Standard DNV-OS-C401, Det Norske Veritas, Oslo.
Erbrich, C.T., Barbosa-Cruz, E. & Barbour, R. 2010. Soil-pile interaction during extrusion of an initially deformed pile.
Proc. of 2nd International Symposium on Offshore Geotechnics, Perth, 489-494, Taylor & Francis, London, Australia.
HSE 2001. A Study of Pile Fatigue During Driving and In-Service and of Pile Tip Integrity. Offshore Technology Report
2001/018, Health and Safety Executive, UK, published by Her Majesty’s Stationery Office, Norwich.

A Brief CV of Professor Mark RandolphMark Randolph holds the Fugro Chair in Geotechnics in the Centre for Offshore Foundation
Systems at the University of Western Australia. His two main research interests are piled
foundations and offshore geotechnics, co-authoring books in each area, Piling Engineering, now
in its third edition, and Offshore Geotechnical Engineering, as well as over 250 journal articles.
Professor Randolph interacts closely with industry, both in research and through his role as
Technical Authority within Fugro AG. He is a Fellow of several learned academies, including theRoyal Society and the Australian Academy of Science. He is a former Scientist of the Year inWestern Australia and holds an honorary doctorate from ETH Zurich.

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