BLUE Hammer Facilitates Pile Driving of Offshore Monopiles with Secondary Steel Attached
1, Henrik Bisgaard Clausen2
1Fistuca, Delft, The Netherlands, 2Ramboll, Copenhagen, Denmark
A new concept for impact driving of monopiles has been developed and tested with success by Fistuca. The so-called BLUE Hammer uses acceleration of a water column by combustion of a gas mixture and the related reaction forces to drive the pile into the ground. A combustion pushes a water column in the air after which it falls back on the pile, delivering a second blow. Whilst a relatively large amount of energy is delivered to the pile, the process of the combustion and rebounce of the water column is relatively slow and will not excite vibrations in the monopile or possible attachments.
This paper will explain the working principles of the hammer and the potential benefits of having secondary attachments mounted on the monopile even before pile driving is performed as well as the methods employed for the verification of the effectiveness and safe operation of the hammer.
A modified version of the geotechnical drivability program GRLWEAP is used to assess the drivability i.e. number of blows and risk of refusal for a monopile on typical soil conditions.
The dynamic finite element program LS-DYNA is used to calculate the stress response of the monopile subjected to the loads from a single blow of the hammer. These stresses are in turn converted into driving fatigue damage by use of rainflow counting and relevant S-N curves for DNVGL-RP-C203.
Based on a generic monopile design and a typical North Sea site, Ramboll has demonstrated with geotechnical driveability calculation and the dynamic finite element method, that monopiles can be driven with this hammer and that it can be done with pre-mounted attachments like boat landings, internal platforms and ICCP equipment.
The BLUE hammer allows for monopile designs without transitions pieces and will save time during installation of the foundations and will eliminate the need for a transition piece skirt to support the boat landing.
The audience will learn about an alternative pile driving method that will allow for simplified design and improved installation time of monopiles. The presentation will showcase the concepts of the hammer and the tools of how to make general assessment of fatigue damage from pile driving.