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Christian LeBlanc Thilsted
Head of Geotechnical Engineering, DONG Energy Wind Power
Vibro-driving monopiles - a feasible installation concept for the future?
Contact details:
E-mail: [email protected],
Phone: +45 99552558
Geotechnical Engineering in Offshore Wind,
Danish Geotechnical Society seminar
Tuesday 1st of April 2014
Vibro-driving of large diameter offshore piles
Why use vibro-driving technique?
Noise emission of conventional pile driving of XL monopiles exceeds acceptable
noise levels in Germany
Vibro-driving is potentially a cost-effective and low-noise alternative to pile driving!
Current status of vibro-driving - a mature technology?
Extensively used on-shore
Installation proven for very large diameter piles
Vibro-driving was used for OWT monopiles
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Quad Kong, 12 m diameter pile in China (apevibro.com) Extensive on-shore use (tuenkers.com) APE vibrator, Borkum Riffgat (offshorewind.biz)
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Main challenges of vibro-driving
Robustness of installation • How to ensure sufficient penetration depth?
• Prediction of installation process?
Noise emission • How to predict noise-emissions during vibro-driving?
Lack of design guidelines • Lateral soil-structure stiffness
• Lateral pile capacity
• Axial pile capacity
Cost-effectiveness of installation • Excess crane capacity needed
• Impact-driving is required
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
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1/3 octave freq (Hz)
Energ
y s
pectr
um
(dB
/ o
ct)
Hammer energy is ~ 400 kN-m and point source depth is 15.9 below sea
r=750A, d@3m, SEL=171.9 dB
r=750A, d@10m, SEL=172 dB
r=750B, d@3m, SEL=168.8 dB
r=750B, d@10m, SEL=166.4 dB
SF - r=750, d@3m, SEL=170.6 dB
SF - r=750, d@10m, SEL=169.1 dB
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Aim and objectives
• To establish knowledge of how to
geotechnical design of vibro-driven
monopiles in typical German North Sea
sands
• To determine noise levels emitted
during vibro-driving
• To gain experience with the vibro-
driving installation process
Two vibro-driving trials were conducted at Anholt OWF
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Vibratory equipment
Three 200 Kgm
vibrators from PTC
Vibro-driven
monopiles
Monopile C12 Monopile P02
Water depth 17.0 m 18.1 m
Monopile weight 277 t 272 t
Monopile diameter 4.69 m - 5.35m 4.69 m - 5.35 m
Monopile length 49.7 m 49.6 m
Seabed
penetration
20.2 m 19.0 m
Soil-conditions at test site
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Soil conditions at demostration sites were
representative for typical dense North Sea Sands
Anholt: P02
Anholt: C12
- in comparison to North Sea Sands from Borkum Riffgrund 1 and Gode Wind 1
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Planned vibro-
driving depth
Final penetration
depth
Vibro-driving was more effective than predicted
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Predicted Pile refusal
Predicted installation:
Size of vibrators too small
Refusal depth at 8m
Refusal at 2 m before planned penetration depth
Planned penetration depth achieved
C12 P02
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Seabed
Planned vibro-
driving depth
Final penetration
depth
Vibro-driving was more effective than predicted
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
C12 P02
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Seabed
Why are installation predictions wrong?
Current methods for vibro-driving prediction can not be used for
large diameter monopiles. More accurate methods are needed…
Plugged? vs. Un-plugged? Effect of pile toe?
Other reasons?
Soil-structure stiffness was measured in-directly
Structural dynamics provides valuable information on soil stiffness
properties
The natural frequency of first order mode is predicted using best-estimate
engineering modelling
The as-built natural frequency is measured using a nacelle accelerometer
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Prediction Measurement
0.324 Hz
0.311 Hz
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Lateral soil-stiffness higher than driven piles
Monopile P02 (vibro-driven)
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Monopile C12 (vibro-driven)
Vibro-driven pile
The lateral soil-structure stiffness of vibro-driven piles
can be predicted equally to impact-driven piles
Vibro-driven pile
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Over-turning pile capacity is equal or higher than driven piles
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Lateral soil stiffness of vibro-
driven piles is measured equal
(or higher) than comparable
impact-driven piles
Lateral soil capacity must be
equal (or higher) than
comparable impact-driven piles
No indications of sand
loosening, instead, slight sand
compaction may have occured
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Validation of axial pile capacity should not require driving
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Vibrator Noise-mitigation shield Hammer
http://capehollandgroup.com/
Riffgat Offshore Wind Farm
How to proof axial pile
capacity?
Validation of axial pile capacity should not require driving
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
(Ex.: Noise Mitigation
Shield from IHC) (Ex.: Hammer from IHC)
+ +
Not cost-effective • Too high mobilisation costs
• Too high installation costs due
to increased installation time
(Ex.: Vibrator from PTC)
Cost-effective
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Vibro-driven monopile at Anholt OWF:
The axial capacity of vibro-driven
monopiles in dense North Sea sands
is not critical
Predicted axial capacity
(ICP05-method):
120 MN
Conservative assumption:
"Vibrodriving cause 50% reduction
of axial capacity"
Predicted axial capacity of vibro-
driven pile: 60MN
Characteristic axial loads:
10 MN
Overall safety factor
6 (!)
Experience from Borkum
Riffgrund 1 sub-substation
installation:
• North Sea sands,
• 4 piles tested using
dynamic pile load testing
ICP05-method was proven to provide a
lower-bound prediction of axial capacity
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Prediction of axial capacity in dense North Sea sands
The axial pile capacity of vibro-driven piles
is 60 % to 110 % of an impact driven piles
Main conclusions from Anholt trial tests
Vibro-driving tests at Anholt
were performed in sands
comparable to dense North
Sea sands
Installation more effective than
predicted, but very dense sand
layers pose a challenge for the
installation process
The lateral stiffness and
capacity of vibro-driven
monopiles in dense sand
should be predicted using
design guidelines developed
for impact-driven monopiles.
The axial capacity of monopiles
in dense sand is not critical and
it should not be a requirement
to validate axial capacity using
impact-driving.
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
Potential of
vibro-driving
Main challenges
Trial tests at
Anholt OWF
Results from
Anholt OWF
Conclusions from
Anholt OWF
Future work on
vibro-driving
Future work on vibro-driving
Vibro-project: An RWE Innogy led
discretionary OWA project
Six large piles (L=21 m, D=4.3 m) are to be
installed on the site; three are to be vibrated,
and three to be rammed. The pile are to be
laterally loaded. installation in Q2 2014.
The project is lead by RWE Innogy, and
supported by the Carbon Trust and developers
including Dong Energy.
Christian LeBlanc Thilsted, November 2014, [email protected] , DONG Energy Wind Power
FLOW R&D project: Alternative
foundation installation
Three driven, three drilled and three
vibrated piles of around ø1,82 m and 15-18
meters length will be tested according to a
predefined test protocol and a Letter of
Approval of DNV.
The project is lead by Ballast Nedam and
supported by the FLOW R&D program in
the Netherlands.
Thank you
Geotechnical Engineering in Offshore Wind - how can we contribute to lowering the cost of electricity?
DGF Seminar, Gentofte, 1st April 2014
For any enquiries regarding potential collaboration and
opportunities etc. with DONG Energy Wind Power,
please contact: Christian LeBlanc Thilsted
(Head of Geotechnical Engineering)
Tel. +45 99 55 25 58