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The main principles of GBM Works’ new monopile installation methodology is created in the SIMPLE development period. This can be described as follows:

  • Using the new Jet-gun technology to reduce the inside shaft friction during pile driving by injecting water in a controlled manner. The process of water injection is two-fold;

    • Jetting water to loosen the soil that enters the inside of the pile.

    • Uniformly fluidize the soil inside the pile to remove the inside shaft resistance.

  • Vibrating in an axial (up and down) direction to reduce the outer shaft friction and tip resistance.

The combination of GBM Works new Jet-gun technology and any vibro-hammer is termed ‘Vibrojet®’.

The main goal of the SIMPLE I project was to determine the basic functionalities of the Jet-gun in sand and determine its added benefit compared to an ordinary vibro-hammer installation. This is done by doing quantitative tests in the lab and 52 qualitative tests in the field.

Lab Tests

Water injection is not new in the industry. However, predicting and installation with water injection has never been done. This makes creating a model, that incorporates all the working mechanism of the Jet-gun, complex due to number of variables. With the laboratory tests the qualitative mechanisms were researched and accurate quantitative prediction models have been developed and validated. The developed models are called Fluidflow®.

The following sub questions were investigated during the quantitative test program:

  • Fluidization

    • What are the conditions that create a fluidized mixture of soil?

  • Jetting

    • What are the conditions of a jet that will loosen the soil and transport it to the inside of the pile?

  • Retrievability

    • Can the Jet-gun be retrieved from the bottom of the monopile after installation?

  • Performance

    • What can be learned from a direct comparison between an installation with and without Jetgun in a laboratory environment?

To scale the tests to the field test scale, three different sizes piles were used. As shown in the picture below.

Field Tests

From the tests at the Maasvlakte 2 the following conclusions have been drawn:

  • The average penetration speed of installation with Jet-gun is approximately 4 times higher than installations without Jet-gun.

  • The refusal depth is approximately 2 times deeper with the addition of the Jet-gun.

  • The dummy retrieval tests proof that the inside of the pile is fluidized up until medium scale. The nozzle clogging test proves the flow can be stopped and resumed with minimal clogging of the nozzles.

  • A new method for controlling and detecting seepage needs to be developed

  • A clear reduction in strain is observed, however the strain measurement system needs to be updated.

A more detailed description of this project is included in the publication of GBM Works 'Development of Jet-gun and fluidization enhanced pile installation tools', as this was presented during the 11th International Conference on Stress Wave Theory and Design and Testing Methods for Deep Foundations, Rotterdam 2022.

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Installation of pile at Maasvlakte 2


Overview lab test setups at Deltares


Overview tests at Maasvlakte 2


The objective for the project SIMPLE II was to demonstrate that monopiles at a scale of 1:4 (with a diameter of 2 meter and length of 25 meter) can be brought to the desired depth with a retrievable  Vibrojet® prototype based on the Jet-gun in combination with a standard vibro hammer, creating vibrations while jetting clay away and fluidize the soil inside the pile.

Lab Tests

The laboratory tests of SIMPLE II meant to test the control system, calibrate and validate the Fluidflow® model and prepare for the field tests. Validation of the model was the most important goal of the lab tests as this model was used for the design of the retrievable Jet-gun which was used in the Phase 2 Field tests.

The main goals of the lab tests were:

  • Validating model for waterjet clay cutting

  • Proof of principle of water jet clay cutting in boom clay

  • Verify the functionality of the control system

  • Reliability of the system

  • Duplication and scientific standard

A more detailed description of the laboratory tests is presented in the publication by Deltares & GBM Works 'On the use of jetting and fluidization techniques for the installation of monopile foundations'. This was presented during the second WindEurope Bilbao event, April 2022.


Overview lab test setups at GBM Works lab

Field tests

During phase 2 of SIMPLE II a completely functional Vibrojet® machine has been created and the machine has operated in a nearshore test environment. In this testing phase we proved that it is possible to install a 35m pile with a diameter of 2.2m with our technology and that there is a possibility of fixing the machine properly in the inside of the pile and retrieve it after installation to make a combined Vibratory and Jetting machine which can be lowered in the monopiles.

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Lowering of the Vibrojet® tool


The SIMPLE IIb goals are to further develop the Jetgun technique in combination with the vibratory technique and fabricate a prototype for the Vibrojet® based on the requirements of the full scale project SIMPLE III.


Another part of the SIMPLE IIb project is to design and construct the Vibrojet® prototypes that will be tested in the SIMOX project. Based on the knowledge obtained in the SIMPLE I and SIMPLE II projects, together with additional modelling and the execution of lab tests these prototype(s) will be designed.

After the SIMOX tests we are going to use the acquired knowledge from all projects to design the full scale Vibrojet® prototype for the SIMPLE III project and after testing we want to do a cost assessment of the Vibrojet® technique on full scale, supported by (and validated with) the project results.


We are participating in the SIMOX project, which is a GROW project where the focus lays mainly on finding a technology that is capable of reducing noise that can be detrimental to fauna, but also looking into technologies which could be capable of decommissioning Monopiles at the end of their lifetime.

The main reason for us to join the SIMOX project is to compare the Vibrojet® technology with other technologies such as the Vibratory hammer, Gentle Driving of Piles concept, Blue Piling and the impact hammer on pile driving and bearing capacity.

Thereby our focus for the SIMOX design is on a well-defined Monopile Integration System design, a design which is welded into the inside of the monopile. Which we are also planning to use in the SIMPLE III project.

The SIMOX project has started in 2021, and will finish in 2024. The consortium of project partners is extensive at this moment Boskalis, Deltaris, DOT, IHC, RWE, Seaway7, Shell, Sif, TNO, TU Delft, Van Oord, Vattenval, Cape Holland, Ocean Winds, Ørsted, Siemens Gamesa and us are the partners of the SIMOX project.


The SIMPLE III project will test the Vibrojet® technology in a large-scale offshore environment. The data generated during the project, including drivability and noise measurements, will take GBM’s silent installation method to Technology Readiness Level (TRL) 7 and will provide the outstanding information to complete the Technology Qualification process of the technology.


The SIMPLE III are schedule for October 2024. This concept to be tested in SIMPLE III has been tested on a smaller scale in the SIMPLE I Project with positive results. With the offshore tests, the scalability subject will be addressed. SIMPLE III is the final research project for Vibrojet® technology before it can be applied on a commercial scale. 


In the SIMPLER project we are planning to further develop the retractable Vibrojet® tool. Which is used in the SIMPLE II project and is our wished end goal for the Vibrojet® technology. The main reason we want to design a retractable tool is because this is a more sustainable way than the Monopile Integration System, which sacrifices a substantial amount of steel.



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