vibro-driving of monopiles - experience from anholt ... · pdf filevibro-driving of large...

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

http://www.google.dk/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=lprix1EP9bbR5M&tbnid=G0KerWOsmvh9uM:&ved=0CAUQjRw&url=http://championsof2morrow.dk/referencer/&ei=4JliUruMD-PJ4gSDm4CACA&bvm=bv.54934254,d.bGE&psig=AFQjCNGedpU7EsCsqEZ7cjo_u3JTKO51Aw&ust=1382280021513182

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

101

102

103

100

110

120

130

140

150

160

170

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


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


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


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


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


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


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


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


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


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


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


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


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.


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)

[email protected]

Tel. +45 99 55 25 58

mailto:[email protected]

vibro-driving of monopiles - experience from anholt ... · pdf filevibro-driving of large...

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