FIELD OF THE INVENTION

The present invention is in the field of a pile foundation used for supporting buildings and the like. Piles can be used as support for onshore or offshore structures, such as tall buildings and wind turbines. The present invention is in particular suited for driving any size of piles, which are often used in softer, non-cohesive, soils, such as sandy soils.

BACKGROUND OF THE INVENTION

The present invention is in the field of pile driving. Typically piles are driven into the soil using hammers or weights dropping repeatedly on top of the pile. In regions with relatively soft soils, or where piles are needed as supports for man-made structures or the like, a relatively large number of piles is driven into the soil. This driving causes noise nuisance to the environment. In addition such driving inflicts forces on the pile, which may weaken or damage the pile.

GB 1066247 (A) recites a vibratory -hammer for driving members, such as piles, having a vertical and rotary action and comprising two shafts mounted on a support housing, and provided with gears and discs, the gears and discs being fitted with weights so that, upon rotation of the shafts in opposite directions, they exert a vibratory turning moment on the support housing thereby rotating it and at the same time, causing a percussive member to strike an anvil portion of the housing. The document is more concerned with drilling using rotational vibration of the pile around a horizontal axis (somewhat confusingly referred to as torsion). In addition the rotation of the respective masses is coupled (see figs. 1-4) and takes place at comparable frequencies. US 3 583 497 A and CN 110 424 384 B relate to further background art.

Recently gentle driving of piles was developed using vibrations. WO 2021/040523 Al describes a shaker thereto. It uses a combination of vertical and torsional vibration. It is advantageous to get rid of the vertical vibrations because of the undesired ground vibrations and noise. However, purely torsional excitation is not always able to ensure driving of the pile to final penetration. So, in many cases and circumstances the shaker performs adequately, but not always.

The present invention therefore relates to an improved pile and pile driver and a method for driving piles, which solves one or more of the above problems and drawbacks of the prior art, providing reliable results, without jeopardizing functionality and advantages. SUMMARY OF THE INVENTION

It is an object of the invention to overcome one or more limitations of piles and pile drivers of the prior art and methods of driving piles and at the very least to provide an alternative thereto. Pile friction with the soil typically is considered to consist of two components: shaft resistance (along the side of the pile) and toe resistance (underneath the pile). The first one is naturally minimized by the torsional vibrations, hence solved mostly by the shaker for gentle driving of piles. The second one cannot be overcome by torsional excitation. In the present invention in particular toe resistance is minimized by modifying the profile of the pile toe. Such a pile profiling can be done in several manners. The present invention thereto relates in a first aspect to a support monopile for gently driving into a soil, wherein the monopile is made from a first material selected from concrete, from a metal, such as iron, and combinations thereof, comprising a monopile toe driving resistance reducer, wherein the toe resistance reducer is selected from circumference discontinuations, a circumference continuous profile, a hardened coating, and combinations thereof, in particular a monopile with a length of 5-100 m, and a diameter of 0.5-20 m. Therewith the resistance of driving the monopile into the soil is decreased, typically by 10-90% relative to a monopile without a resistance reducer, in particular by 20- 50%. It is found that toe resistance can be minimized, or at least decreased, by modifying a profile of the pile toe. Such a pile profiling can be done in several manners: making teeth (discontinuous profile) of various shapes, making smooth (continuous) profiling (e.g. wave-shaped), decreasing a pile thickness at the toe section (e.g. making its edges "sharper"), by applying non-adhesive coatings, wherein the term “non-adhesive” is used in view of surrounding soil, ensuring that soil does not stick to the pile toe, by applying hardening coatings at the pile toe, and by any combination of the above. Exact modifications typically depend on pile dimensions on the one hand and soil properties at the other hand. For the different soils, qualitatively different pile profiling can be applied. An additional advantages is the improved driveability of the present monopile, thus faster installation reducing offshore construction vessel time and therefore reducing the large amount of the wind park installation costs. It is further found that a bearing capacity of the present monopile is mainly determined by the shaft resistance, whereas the toe plays a minor role herein. Also, it is noted that by performing standard tests to measure the pile bearing capacity helps either in determining the minimum allowed wall thickness or even in confirming that toe geometry has no effect on the eventual pile bearing capacity.

In a second aspect, the present invention relates to a shaker (1) for gentle monopile driving comprising a fixator (9) for mechanically fixing a vibrator (3) to a monopile, at least one actuator (4), a vibrator (3) characterized in that the vibrator is configured to provide vertical vibration of the monopile at a first vibration frequency and torsion to the monopile at a second torsion frequency, a controller for driving the at least one actuator (4), and in particular a monopile according to the invention. The term “frequency” is used to relate to any form of (vibration) repetition, which may be sinusoidal, a combination of sinusoidal repetitions, complex (vibrational) forms, and so on, depending on the vibrators used and operational mode(s) thereof.

In a third aspect, the present invention relates to a method of driving a monopile into a soil, comprising providing a shaker (1) according to the invention, mounting the shaker (1) on a monopile according to the invention, and driving the monopile into the soil.

In a fourth aspect, the present invention relates to a kit of parts comprising a shaker according to the invention comprising at least one of a fixator (9), a vibrator (3), at least one actuator (4), a controller, and a monopile according to the invention.

The present invention may be considered to relate to a shaker causing torsional vibrations with around a vertical axis, in combination with vertical vibration. The torsional vibrations typically take place at a much higher frequency that the vertical vibrations and are considered to continuously break static friction of the pile with surrounding soil. As the coupling between the present pile and the surrounding soil is broken the vertical vibration drives the pile into the soil. In a first aspect, the present invention relates to a shaker for gentle pile driving comprising a fixator for mechanically fixing a vibrator to a pile, and thus for transferring vibrational energy to the pile, a vibrator adapted to provide vertical vibration of the pile at a first vibration frequency and torsion to the pile at a second, typically much higher, torsion frequency, wherein the vibrator comprises at least two groups i>2 of eccentric masses, each group i comprising at least two equal masses), wherein each individual mass mij is positioned at a distance di from the vibrator, typically a distance parallel to a rotation axis, such as at a distance di and d2, wherein the mass mij is attached to at least one horizontal axis hai, at least one motor for rotating the masses mij around their horizontal axis hai, such that in a group i masses mij rotate at a same angular velocity Oi along said horizontal axis hai, wherein angular velocity Oi is different from angular velocity coi+i, typically wherein the torsion frequency is larger than the vertical vibration frequency, typically several times larger, and in a group i+1 masses mi+ij rotate at an opposite angular velocity Oi+i along said horizontal axis hai+i, and a controller for driving the at least one motor, for controlling each individual angular velocity Oi of group i of masses mij, for controlling a sum of horizontal forces produced by the respective masses, and for balancing a sum of vertical forces produced by the respective masses. In addition to these forces gravity pulls the mass of the pile downwards. As such the controller may balance forces in the z-direction, and sum forces in the x-direction (or equivalently, in the y-direction, or in a combined x+y-direction), the z-direction being parallel to the axis of the pile, and the x- and y- direction being perpendicular to the axis of the pile, such as in a Cartesian set of axes. The shaker can drive piles into the soil by means of torsional vibration, typically at high frequencies(or vibration modes in case the excitation is hon-harmonic), in combination with vertical vibration, typically at lower frequencies (or vibration modes in case the excitation is hon-harmonic). No further driving means are required, such as a hammering device. Thereto the eccentric masses rotate at typically high speed. Typically the masses are positioned such that at a specific position they generate two forces of opposite directions creating a moment in the torsional direction, along the longitudinal axis of the pile, and zero forces in another position. The shaker, and the present method, are more rapid and less noisy. For instance for a midsized pile of e.g. 10 m length and with a diameter of about 75 cm the pile is driven about twice as fast compared to prior art techniques. The pile may move downward with a speed of some 30 cm/second. In addition no or less deformation of the pile is achieved, compared to an impact hammer. The energy generated by the present shaker is mainly used for driving the pile. Reference is made to the above WO 2021/040523 Al, of which the contents are incorporated.

Advantages of the present description are detailed throughout the description. DETAILED DESCRIPTION OF THE INVENTION

Some typical dimensions and characteristics for a wind turbine may be: DNV-OS-J101-2007: Design of offshore wind turbine structures DNV-RP-C203: Fatigue design of offshore steel structures Steel grade: S355 Yield strength: 355 MPa Modulus of elasticity E = 210 GPa Poisson’s ratio v = 0.3

Coefficient of linear thermal expansion (T < 100 °C) a = 12e-6 K-l Partial material factors:

- Ultimate limit state strength checks, ys = 1.10

- ULS buckling check, ys = 1.20

- Serviceability limit state, ys = 1.00

- Seismic ultimate limit state, ys = 1.15 Model: REpower 5M (5.0 MW)

Turbulence intensity Class: IEC lb /GL offshore type class I Structural design lifetime: 25 years Hub height: 85 m above MSL Blade Tip Height: 153 m above MSL

Rotor Diameter: 126 m

Swept Area: 12’469 m ²

Mass of nacelle (without rotor): 290 tonnes (approx.)

Rotor: 120 tonnes (approx.)

Cut-in Wind Speed: 3,5 m/s

Rated Wind Speed: 13,0 m/s

Cut-out Wind Speed: 30 m/s

Operational rotor speed: 7.7 - 12.1 rpm

Nominal rotor speed: 10.5 rpm

Structure Type: Steel Tubular

Tower Dimensions

BASE: D=6.00 m, t = 35 mm

TOP: D=4.50 m, t = 20 mm

Mass initial estimate =71*5.25*0.0275*70*7 ,850 = 250 t

In an exemplary embodiment of the present monopile the circumference discontinuations are provided in a longitudinal direction of the monopile, wherein 1- 10 circumference discontinuations are provided, wherein each circumference discontinuations individually has a height of 0.5-50 cm and a length of 0.5-50 cm.

In an exemplary embodiment of the present monopile the circumference continuous profile is provided in a longitudinal direction of the monopile, wherein 1- 10 circumference continuous profiles are provided, wherein each circumference continuous profile individually has a height of 0.5-50 cm and a length of 0.5-50 cm.

In an exemplary embodiment of the monopile the decreasing thickness of the monopile is 0.1-50% of the diameter.

In an exemplary embodiment of the monopile the sharp edge has an edge width of 0.2-10 cm.

In an exemplary embodiment of the present monopile the hardened coating is selected from alloys, such as Si-alloys, such as SiC.

In an exemplary embodiment of the present monopile the monopile comprises a second material, wherein the second material is incorporated in the first material, wherein the second material is selected from polymers, resins, such as epoxy resins, graphene, and carbon nanotubes.

The above exemplary embodiments provide for a reduction in resistance when driving the monopile into the soil, as mentioned.

In an exemplary embodiment of the shaker the vibrator comprises at least two groups i>2 of eccentric masses, each group i comprising at least two equal masses), wherein each individual mass mij is positioned at a distance di from the centre of rotation of the vibrator, and wherein a mass mi _;i on one side is displaced 180 degrees with respect to a mass m,.2 on the other side, or wherein masses mi _;i and m,.2 counterrotate, wherein the mass mij is attached to at least one horizontal axis hai, wherein the at least one actuator (4) is for rotating the masses mij around their horizontal axis hai, such that in a group i masses mij rotate at a same angular velocity Oi along said horizontal axis hai, and in a group i+1 masses mi+ij rotate at an opposite angular velocity Oi+i along said horizontal axis hai+i, wherein angular velocity Oi is different from angular velocity C0i+i, wherein the controller is configured for controlling each individual angular velocity Oi of group i of masses mij, for controlling a sum of horizontal forces produced by the respective masses, and for balancing a sum of vertical forces produced by the respective masses.

In an the present shaker the vibrator comprises at least one pair of at least two vertically oriented equal masses configured to move in a reciprocal manner, in particular linear actuators, such as linear pistons vpij and at least one horizontally oriented mass configured to move in a reciprocal manner, such as at least one pair of at least two horizontally oriented equal masses configured to move in a reciprocal manner, in particular linear actuators, such as linear pistons hpij, wherein each individual piston is configured to provide linear motion of a cylinder thereof, wherein the cylinders of the at least two vertically oriented masses configured to move in a reciprocal manner, such as linear pistons vpij are each individually configured to operate at a frequency CDvpi providing a reciprocating vertical velocity rv _v; , wherein the cylinders of the at least two horizontally oriented masses configured to move in a reciprocal manner, such as linear pistons are each individually configured to operate at a frequency CDhpi providing a reciprocating horizontal velocity rh _VJ , wherein in each pair cylinders are configured to move in opposite directions, such as 180 degrees out of phase, and wherein in each pair of linear pistons wherein each piston individually is located at a distance di from a centre of rotation of the vibrator. The movement in reciprocal manner is in a vertical direction or in a horizontal direction respectively. The mass may be driven by an actuator, such as in a piston wherein a mass is extracted and retracted, a motor, such as an electrical motor, and so on. Likewise, any pair of reciprocating masses, as the cylinders, can be used. Provided is thus a vertical cylinder located in the centre. It provides vertical vibrations (see the arrows in fig. 4a). By varying (typically by selecting) the stroke of a cylinder the amplitude may be adapted, and by varying the speed (typically by controlling) of its movement, the frequency o _Pi may be adapted. In this way, the frequency and the amplitude remain independent from each other. In principle, more vertical cylinders may be used. If more are used, they are positioned equidistantly from the centre of the pile, at least pairwise, and optionally all. The same goes for the horizontal cylinders. They are positioned tangentially, hence horizontal, to the to be driven pile. The strokes are synchronized, operating at the same frequency, but in opposite directions, such as 180 degrees out of phase, that is, one moving in a first direction, the other moving in the opposite direction thereof (see the green and the red arrows; the colour designates the different between the extraction and retraction). There might be more cylinders placed over the pile. They extend and retract synchronously. The vertical and horizontal cylinders (or pistons) may operate at different frequencies, and typically Ohpi^Ovpi for any given horizontal and vertical pair. Also an array of the cylinders may be considered; therein each set or pair (e.g. horizontal cylinders) may have sub-sets operating at different frequencies (e.g. 50% of cylinders operating at a higher frequency and 50% operating at a lower one and so on). In this way, a not purely sinusoidal vibration is generated, and vibrations of a more complex form can be provided, if required. Linear actuators may be selected from hydraulic cylinders, electrical cylinders, pneumatic cylinders, and from piezoelectric stacks.

In an exemplary embodiment of the present shaker a centre of mass of the shaker and a rotation axis of the pile may coincide, typically within a few%, such as within 5%.

In an exemplary embodiment of the present shaker may comprise a least one gear adapted to be driven by the at least one actuator and adapted to rotate at least one mass mij, preferably two masses within one group i. Therewith good and simple control of forces can be achieved, as well as adaption of forces during pile driving. In an example masses of different groups may be driven by the same gear.

In an exemplary embodiment of the present shaker a first group may comprise a mass mi,i and a mass mi, 2, a second group may comprise a mass m2,i and a mass m2, 2, and optional further groups may comprise a mass mi,i and a mass mi, 2. So a large variety of masses may be used, as well as a number of groups. Typically, in view of simplicity of construction only a limited number of groups is used, such as two, but the invention is not limited thereto.

In an exemplary embodiment of the present shaker the controller may be adapted to control the sum of vertical forces of the groups to be cancelled. By varying angular velocity and typically by carefully selecting and balancing masses, and radius and/or distance, the sum of vertical forces is cancelled. Such results in a very steady mode of operation with a minimum amount of noise.

In an exemplary embodiment of the present shaker the horizontal forces may be controlled to be added. As with the vertical forces, horizontal forces can be controlled by varying angular velocity and typically by carefully selecting and balancing masses, and radius and/or distance.

Also, vertical forces may still be generated, such as at low frequency. In any case the mass of the pile, and gravitational force, in combination with the torsion, drives the pile into the soil.

In an exemplary embodiment of the present shaker in an i ^th group a first mass mu may be located at a first distance di from a vibrator side and a second mass mi,2 may be located at the same first distance di from a vibrator side opposite of the first mass. In a group masses are typically located “opposite” of one and another, with respect to the position of the vibrator.

In an exemplary embodiment of the present shaker the at least one actuator may be each individually adapted to rotate horizontal rotation axes hai at 10-200 Hz (600- 12000 rpm), preferably at 20-180 Hz, more preferably at 30-150 Hz, even more preferably at 40-120 Hz, such as at 50-100 Hz, e.g. 60-80 Hz.

In an exemplary embodiment of the present shaker at least one first actuator may each individually be adapted to rotate horizontal rotation axes hai at a first vibration frequency of 10-50 Hz (600-3000 rpm), preferably at 12-30 Hz, more preferably at 15-25 Hz, such as at 16-24 Hz.

In an exemplary embodiment of the present shaker at least one second actuator may each individually be adapted to rotate horizontal rotation axes hai at a second torsion frequency of 15-200 Hz (900-12000 rpm), preferably at 30-150 Hz, more preferably at 50-100 Hz, such as at 60-80 Hz.

In an example the first vibration frequency may be 1400 rpm and the second torsion frequency may be 4800 rpm.

In an exemplary embodiment of the present shaker at least one second angular torsion velocity Oi may be at least two times first angular vibration velocity coi+i, preferably wherein at least one angular velocity Oi is at least four times angular velocity coi+i, more preferably at least ten times, such as at least 50 times.

In an exemplary embodiment of the present shaker masses mi,i and mi,2 may be located at a distance eifrom horizontal rotation axis hai, and wherein masses mi+i,i and mi+i,2 may be located at a distance ei+i from horizontal rotation axis hai+i.

In an exemplary embodiment of the present shaker wherein masses mij may be disc-shaped with a radius of eiand wherein a centre of mass of the disc-shaped mass coincide with the rotation axes hai, respectively. Therewith a well-balanced mass may be provided.

In an exemplary embodiment of the present shaker the ratio of masses mi+i,i/mi,i may be equal to ei/ei+i . Therewith forces of an i ^th group and an i+l ^th group can be balanced, typically well within 1% or better, such as fully balanced.

In an exemplary embodiment the present shaker may comprise two groups of masses, wherein the horizontal rotation axes hai and ha2 are at equal distance from a central point of the shaker. Therewith forces of an i ^th group and an i+l ^th group can be balanced. In an exemplary embodiment of the present shaker masses may be disc shaped. Such is found to be easily attached to the axes.

In an exemplary embodiment of the present shaker the masses may be 5-5000 gr, preferably 10-1000 gr, such as 30-600 gr, e.g. 50-400 gr. For larger piles and/or heavier soils and/or stiffer soils larger masses may be used. In addition, or as alternative, angular velocities may be increased.

In an exemplary embodiment of the present shaker the distance/radius er is 1-50 cm, preferably 2-40 cm, such as 3-30 cm.

In an exemplary embodiment of the present shaker the controller may drive the at least one actuator in phase, for instance such that F _Z I=-F _Z 2, typically well within 1% accuracy, such as fully equal of size.

In an exemplary embodiment of the present shaker the shaker may comprise a receiving structure, such as a groove. Therewith the pile can be firmly attached to the present vibrator.

In an exemplary embodiment of the present shaker the controller may be adapted to provide a vertical driving frequency of 10-50 Hz.

In an exemplary embodiment of the present shaker the shaker is configured to adjust at least one distance di, in particular wherein the shaker is configured to adjust all distances di.

In an exemplary embodiment of the present shaker the fixator (9) is configured to fix the shaker outside to the monopile, inside to the monopile, over an edge of the monopile, and combinations thereof

In an exemplary embodiment of the present method the vibrator is calibrated before driving the pile into the soil. As such driving forces, angular velocities, soil properties, interaction between pile and soil, and so on, can be controlled better.

The invention will hereafter be further elucidated through the following examples which are exemplary and explanatory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

SUMMARY OF THE FIGURES

Figs. 1, 2, 3a-d show some details.

Figs. 4a-g shows an alternative embodiment, comprising pistons.

Figs. 5a-b show exemplary monopiles.

Figs. 6a-c show experimental results.

DETAILED DESCRIPTION OF FIGURES

In the figures:

1 shaker 2 axle

3 vibrator

4 actuator

8 bearing

9 fixator

18 gear

21 clamp

22 axle

25 gear

26 clamp

27 engine

29 gear

31 safety clamp

32 ball bearing

33 spacer

34 spacer

35 clamp

36 support + fixator

43 support + fixator di distance i of mass mij from a vibrator side ei distance i of mass mij from a horizontal rotation axis hai hai horizontal axis i mij mass j of group i co i angular velocity i

Figure 1 shows an example of a prototype of the present shaker mounted on a pile. The main block was machined as to accommodate the main components of the shaker (actuator, gears, axles and masses) in an efficient way and to ensure that the centre of masses falls in the desired place. The shaker consists of a actuator that provides the input energy. Three gears are used to transfer the forces from the actuator to the two axles that contain four eccentric masses in total, two per axle. When the masses start rotating centrifugal forces are generated and these are transfer to the pile in the form of a torsional moment.

Figure 2 shows a top view sketch of the prototype shaker that reveals the relative spatial positions of masses and principal distances (di, d2, ei, 62) from the block. Examples

Here details of a design and functioning of a small scale shaker are described. Also an explanation of how the shaker works is given, as well as a technical drawing with an overview of the mechanical components of the shaker, a description of a frequency controlling system of the electrical actuator, a parametric study of the expected forces and moments generated by the shaker is shown, and some safety recommendations and instructions are addressed.

The shaker is designed to be mounted on the top of a small scale pile as shown in Fig 1. The shaker generates forces by means of counter-rotating masses displaced certain distance from the centre of rotation. And, pairing this forces with another’s of the opposite sign a moment is generated. This moment is only effective about the z- axis according to Fig. 1. This means that the moment only applies when the masses are in the position shown in Fig. 1, and rotated 180 degrees with respect to the drawn position. This generates a harmonic torsional moment that is transferred to the top of the pile. The system is driven by an electrical actuator frequency controlled. Also a feedback loop may be provided, providing actual force and/or angular rotation as measured, comparing said measurement with present values, and optionally correcting for measured variation, such as by increasing or decreasing the angular velocity. Such may be done for the total system, or for parts thereof, such as for a group of masses i. Moreover, the masses and the positioning is variable. This gives us enough flexibility to generate the desired moment. The components were selected such that enable the correct functioning of the shaker for a long period of time. The figure 3 depicted below shows the technical details of the final prototype design of the shaker.

The force F _z , created by one rotating mass is cancelled out at all 9 by the force generated in the other axle that runs in counter phase, and the same happens in the other part of the axles. In the case of F _x , the force is cancelled out in all 9, but at 9 and 189 degrees, where F _x is maximum. Given the fact that the two masses on one side are displaced 189 degrees with respect to the two masses on the other side, a moment about the z-axis is generated. The reason for using two masses at each side of the shaker is to eliminate the moment generated about the x-axis, when the masses are at 99 and 279 degrees with respect to the origin (which is considered to be in the position shown in the drawing). Given that, the eccentric distances are different the masses have to necessarily be different as well. Considering that the axles are aligned in the x-direction no moment about the y-axis is expected. Finally, the force and moment development in the whole envelope is shown in the following figures as an example for a specific case study.

The figure 2 represents the shaker and describes the parameters of interest for the analysis. For the case study the following values are selected: mi=19 gr, ei=5 cm, e2=8 cm, di=10 cm, di=l 5 cm, and m2=miei/e2=6.3 gr. The mass m2 is computed such that the resultant moment about the x-axis is zero given that the distances di and d2 have to be different for practical reasons of spacing. The resultant decomposed forces in the x- direction are as a consequence summed, whereas the decomposed forces in the z-directions cancel one and another and are 0 in total.

In the figure 3a-d the components that compose an example of the present prototype shaker are enumerated and hereafter a description of the utility of each component in the shaker is given. Component 27 corresponds to the engine that provides the power and enables the moving of the eccentric masses. Components 43 and 36 consist of a supporting plate and fixations for the engine that ensures the correct positioning of the engine shaft with the driving axle gear, 29, and the clamping, 35, to avoid slippage between the engine shaft and the driving axle. A train of gears, 18 and 25, is used to transfer the engine torque to the axles, 2 and 22. To ensure the correct alignment between the gears a safety clamp is used in the powered gear, 31. A clamp, 26, is used to ensure the eccentric masses are kept in place during the movement of the axles. In the side view of the figure, components, 8 and 21, consist of the bearing and clamps respectively.

Figure 3c shows the top view of the shaker. Component 32 consists of a ball bearing to allow the rotation of the engine axle, and, components 33 and 34 consist of spacer rings to ensure the correct coupling between the components of the power train.

The actuator of the shaker can reach high speeds, therefore, it typically is extremely important to take some safety measures before activating the shaker. 1.- The exchangeable parts such as the added masses and constraining bolts have to be ensured in order not to fly away during operation. Even then, during operation some protections should be provided and no person should stand close to the shaker. 2.- The simulated maximum force generated by the shaker during operation on the axles is: 400 N (per eccentric weight). Any misalignment can cause a small bending of the axle making the shaker unstable and its behaviour unpredictable. It is therefore preferred to use disc-shaped masses with a centre of mass and rotation axis coinciding, or to use two equal masses at equal distance from the axis. 3.- The gears are fixed to the axles by a set screw. To avoid scratching the axle a small piece of copper is placed between the set screw and the axle. Care should be taken when the gear is removed that the piece of copper doesn’t fall out. 4.- The axle of the actuator is clamped in the drive axle by a clamp nut (MLN8). Prescribed tightening torque is 24.5 Nm. Herewith a lab-scale pile was driven into the soil multiple times, without any problem.

Figs. 4a-g shows an alternative exemplary embodiment, comprising two horizontally moving pistons 3 and one vertically moving piston 3.

Figs. 5a-b show exemplary monopiles. In fig. 5a a zig-zag profile is shown, in fig. 5b a wavy structure. It is found that these monopiles can be driven into the soil 5- 30% faster (in time) that the same pile without such a toe resistance reductor. This is in addition to the advantages of the present gentle driver of piles over the cited prior art.

Figs. 6a, b show a sinusoidal input signal to the shaker. The wider amplitude shows the responsive torsional vibration signal (t), whereas the smaller one shows the vertical response (v). Fig. 6c shows the penetration depth as a function of time, and as a function of forces applies. In this figure the present GDP is shown at the left. This means that a pile has been driven with the GDP technique. Amongst these, solid line means no profile pile and dashed ones mean sinus profile pile and dashed-dot line profile with teeth toe profile. It is clear from the figure that the present GDP shaker performs much better compared to prior art techniques; in addition, piles with profiles perform even better.