SHAKER FOR GENTLE DRIVING OF PILES

Abstract

The present invention is in the field of piles 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 small- and mid-scale piles, which are often used in softer, non-cohesive, soils, such as sandy soils.

Claims

1. A shaker for gentle pile driving comprising a fixator for mechanically fixing a vibrator to a pile, at least one motor a vibrator characterized in that the vibrator is adapted to provide vertical vibration of the pile at a first vibration frequency and torsion to the pile at a second torsion frequency, wherein the vibrator comprises at least two groups i≥2 of eccentric masses, each group i comprising at least two equal masses j. wherein each individual mass my is positioned at a distance d.sub.i from the vibrator, wherein the mass my is attached to at least one horizontal axis ha.sub.i. at least one motor wherein the at least one motor is for rotating the masses m.sub.i,j around their horizontal axis ha.sub.i, such that in a group i masses m.sub.i,j rotate at a same angular velocity ω.sub.i along said horizontal axis ha.sub.i, and in a group i+1 masses m.sub.i+1,j rotate at an opposite angular velocity ω.sub.i+1 along said horizontal axis ha.sub.1+1. wherein angular velocity ω.sub.i is different from angular velocity ω.sub.i+1, and a controller for driving the at least one motor, for controlling each individual angular velocity ω.sub.i of individual group i of masses m.sub.i,j, 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.

2. The shaker according to claim 1. wherein a center of mass c.sub.m of the shaker and a rotation axis of the pile coincide.

3. The shaker according to claim 1, comprising a least one gear adapted to be driven by the at least one motor and adapted to rotate at least one mass m.sub.i,j, and wherein at least one first motor is each individually adapted to rotate horizontal rotation axes ha.sub.i at a first vibration frequency of 600-3000 rpm, and wherein at least one second motor is each individually adapted to rotate horizontal rotation axes ha.sub.i at a second torsion frequency of 900-12000 rpm.

4. The shaker according to claim 1, wherein at least one second angular torsion velocity ω.sub.i is at least two times first angular vibration velocity ω.sub.i+1, wherein a first group comprises a mass m.sub.1,1 and a mass m.sub.1,2, a second group comprises a mass m.sub.2,1 and a mass m.sub.2,2, and optional further groups comprise a mass m.sub.i,1 and a mass m.sub.i,2, wherein the controller is adapted to control the sum of vertical forces of the groups to be cancelled, and wherein the horizontal forces are controlled to be added.

5. The shaker according to claim 1, wherein in an i.sup.th group a first mass m.sub.i,1 is located at a first distance d.sub.i from a vibrator side and a second mass m.sub.i,2 is located at the same first distance d.sub.i from a vibrator side opposite of the first mass.

6. The shaker according to claim 1, wherein the at least one motor is each individually adapted to rotate horizontal rotation axes ha.sub.i at 600-12000 rpm.

7. The shaker according to claim 1, wherein masses m.sub.i,1 and m.sub.i,2 are located at a distance e.sub.i from horizontal rotation axis ha.sub.i, and wherein masses m.sub.i+1,1 and m.sub.i+1,2 are located at a distance e.sub.i+1 from horizontal rotation axis ha.sub.i+1.

8. The shaker according to claim 1, wherein the ratio of masses m.sub.i+1,1/m.sub.i,1 is equal to e.sub.i/e.sub.i+1.

9. The shaker according to claim 1, comprising two groups of masses, wherein the horizontal rotation axes ha.sub.1 and ha.sub.2 are at equal distance from a central point of the shaker.

10. The shaker according to claim 1, wherein masses are disc shaped.

11. The shaker according to 1, wherein the masses are 5-5000 gr, and wherein distance/radius e.sub.i is 1-50 cm.

12. The shaker according to claim 1, wherein the controller drives the at least one motor in phase.

13. The shaker according to claim 1, wherein the shaker comprises a receiving structure.

14. The shaker according to claim 1, wherein the controller is adapted to provide a vertical driving frequency of 10-50 Hz, and with the proviso that no further driving device is present.

15. (canceled)

16. (canceled)

17. The shaker according to claim 1, wherein masses m.sub.i,j are disc-shaped with a radius of e.sub.i and wherein a center of mass of the disc-shaped mass coincide with the rotation axes ha.sub.i, respectively.

Description

SUMMARY OF THE FIGURES

[0031] FIGS. 1, 2, 3a-d show some details.

[0032] FIGS. 4-5 show the present shaker and forces obtained.

DETAILED DESCRIPTION OF FIGURES

[0033] In the figures: [0034] 1 shaker [0035] 2 axle [0036] 3 vibrator [0037] 4 motor [0038] 8 bearing [0039] 9 fixator [0040] 18 gear [0041] 21 clamp [0042] 22 axle [0043] 25 gear [0044] 26 clamp [0045] 27 engine [0046] 29 gear [0047] 31 safety clamp [0048] 32 ball bearing [0049] 33 spacer [0050] 34 spacer [0051] 35 clamp [0052] 36 support+fixator [0053] 43 support+fixator [0054] d.sub.i distance i of mass m.sub.i,j from a vibrator side [0055] e.sub.i distance i of mass m.sub.i,j from a horizontal rotation axis ha.sub.1 [0056] ha.sub.i horizontal axis i [0057] m.sub.i,j mass j of group i [0058] ω.sub.I angular velocity i

[0059] FIG. 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 (motor, 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 motor that provides the input energy. Three gears are used to transfer the forces from the motor 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.

[0060] FIG. 2 shows a top view sketch of the prototype shaker that reveals the relative spatial positions of masses and principal distances (d.sub.1, d.sub.2, e.sub.1, e.sub.2) from the block. Examples

[0061] 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 motor, a parametric study of the expected forces and moments generated by the shaker is shown, and some safety recommendations and instructions are addressed.

[0062] 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 motor 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 FIG. 3 depicted below shows the technical details of the final prototype design of the shaker.

[0063] The force F.sub.z, created by one rotating mass is cancelled out at all θ 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.sub.x, the force is cancelled out in all θ, but at 0 and 180 degrees, where F.sub.x is maximum. Given the fact that the two masses on one side are displaced 180 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 90 and 270 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.

[0064] The FIG. 2 represents the shaker and describes the parameters of interest for the analysis. For the case study the following values are selected: m.sub.1=10 gr, e.sub.1=5 cm, e.sub.2=8 cm, d.sub.1=10 cm, d.sub.2=15 cm, and m.sub.2=m.sub.1e.sub.1/e.sub.2=6.3 gr. The mass m2 is computed such that the resultant moment about the x-axis is zero given that the distances d.sub.1 and d.sub.2 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.

[0065] In the FIG. 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.

[0066] 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.

[0067] FIG. 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.

[0068] The motor 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 center 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 motor is clamped in the drive axle by a clamp nut (MLN8). Prescribed tightening torque is 24.5 Nm.

[0069] Herewith a lab-scale pile was driven into the soil multiple times, without any problem.

[0070] FIGS. 4-6 show rotation of respective masses, forces obtained over time thereby and torsion Mt. In FIG. 4 two masses (dark sections) are provided at a top section of the shaker. These, partially disc-shaped, masses m.sub.1,1 and m.sub.1,2 rotate at angular velocity ω.sub.1 along said horizontal axis ha.sub.1, therewith providing vertical vibrational forces F5 and F6. Due to the rotating masses the forces F5 and F6 vary. Further, partially disc-shaped, masses m.sub.2,1 and m.sub.2,2 rotate at angular velocity ω.sub.2 along a second horizontal axis ha.sub.2, therewith providing horizontal torsional forces F3 and F4. Likewise, partly visible, partially disc-shaped, masses m.sub.3,1 and m.sub.3,2 also rotate at angular velocity ω.sub.2 along a second horizontal axis ha.sub.2, therewith providing horizontal torsional forces Fl and F2. In an alternative masses m.sub.3,1 and m.sub.3,2 may rotate at angular velocity ω.sub.3 being different from angular velocity ω.sub.2. Forces F1-F4 provide torsion Mt. FIG. 5 shows the direction of forces F5 and F6 depending on position of the masses m.sub.1,1 and m.sub.1,2. In the top left position 1 a sum of masses F5+F6 is downward, in the bottom left position 3 a sum of masses F5+F6 is upward, whereas in the top right and bottom right positions 2 and 4 forces F5 and F6 cancel one and another. In FIG. 6 a similar effect is shown for masses Fl-F4. In the top left position 1 a sum of masses Fl-F4 provide a clockwise torsion around axis z, in the bottom left position 3 a sum of masses Fl-F4 provide an anti-clockwise torsion around axis z, whereas in the top right and bottom right positions 2 and 4 forces Fl-F4 cancel one and another.