The invention also relates to a corresponding device of the type revealed in the preamble to the appended independent means claim.

It is already known in one and the same equipment to apply both striking and vibratory forces on the surface of an area of ground in order to compact the engaged volume of earth. Dutch patent application No.

7415157, for instance, reveals a stamping plate that is in contact with the ground and receives thrusts of high energy from a striking hammer. A ring-shaped vibrating plate is in contact with the ground surface around the stamping plate and supports an active vibrator which includes rotationally driven eccentric weights and which, via a spring devices, supports an inertial mass.

EP 0299118 Al reveals a variant in which the striking hammer is dropped directly to make contact with the ground surface as if controlled on a vertical post, the lower end of which is lowered into the ground, the post being provided at its upper end with an active vibrator.

When laying foundations it may be necessary to either improve the geotechnical properties of the stratum of earth, or reinforce these by installing piles or tongues. The best method of installation depends on the properties of the earth and the load caused by the planned construction.

In certain earth strata, e. g. cohesive soils such as clay, optimal penetration of an object is achieved by a brief impulse (striking hammer). In other conditions, e. g. in non-cohesive soils such as sand and gravel, vibration-

driving piles and tongues or packing the earth with a vibrator is the most efficient method. It is desirable to be able to produce striking and vibration using the same equipment. Such equipment is currently lacking.

A directly operating active vibrator is expensive and has a relatively short useful life due to breakdowns in the bearings for the eccentric weights.

Striking hammers have limited effect, particularly in non-cohesive soils.

One object of the invention is therefore to make available a technique by which the element can be driven by striking and/or vibration in an efficient, and thus-power saving, manner for compacting a material, for driving an element into the material or for pulling an element up out of the material.

Another object of the invention, furthermore, is to provide a vibrating device whose resonance frequency is adjustable so that, for instance, it substantially corresponds to or is at a suitable distance from the natural frequency of the element and of the material area engaged thereby.

The objects are achieved fully or partially by means of the present invention.

The invention is defined in the appended independent method claim.

The invention is also defined in the appended independent means claim.

Embodiments of the invention are defined in the appended sub-claims.

The invention can advantageously be used for compacting earth strata, e. g. non-cohesive material, with the aid of a stamping plate which rests on the ground surface and which is struck by a striking hammer or a vibrator.

Alternatively the invention can be utilized to drive a pile or tongue down into an earth stratum, a hammer striking the pile or tongue, and the pile or tongue being provided with the passive vibrating device. By means of dynamic adjustment using a passive vibrating device (mass-spring-system attached to the object) the object (plate or elongate element) subjected to

the impulse can be set in intensive and prolonged oscillatory movement.

The applied driving energy is thus utilized in optimal manner. In order to achieve effective penetration it is suitable for the passive vibrating device to have a resonance frequency corresponding to the natural frequency of the pile/tongue. When compacting it is suitable for it to be possible for the resonance frequency of the vibrating device to approach the natural frequency of the whole vibrating system. This comprises the engaged earth mass as well as the packing device (plate, pile or packing implement). The elongate object can also be in the form of a packing device and in that case be used to pack the earth.

The vibrating device makes use of the resonance effect which reinforces the applied driving energy and prolongs the duration of the oscillation and gives the driving device an extremely long useful life. Thanks to the invention, the passive energy transmitted from the active energy source towards a plate or an elongate object is re-used and amplified.

The spring device can naturally constitute a part of the mass of the vibrating device. The spring members of the spring device may be designed as helical springs, flexural springs, torsion springs or be in any other suitable and known form for producing the stated motion of the mass. Furthermore the springs may include suitable link arms or mechanisms to produce the stated desired motion.

The energy that sets the vibrating device in vibratory movement can be supplied in various ways, e. g. by applying hammer strokes to the element or to the mass supported by the vibrating device, or by means of a vibrator connected to the mass of the vibrating device.

The invention is not limited to applications in the field of foundation laying, i. e. compacting and inserting or pulling up piles or tongues in earth, but may be used in principle for all types of material compacting and driving all types of rigid objects into material they can penetrate.

An important advantage of the invention is that the technique in accordance with the invention can be combined with conventional equipment for soil compacting and pile/tongue penetration or removal.

Furthermore, the technique in accordance with the invention requires little energy and is extremely robust, i. e. has a relatively long useful life. The oscillation frequency of the vibrating device can advantageously be varied by changing the characteristic of the spring device, e. g. by altering the effective length of the springs or the size of the mass, or by a combination of both these measures.

The natural frequency of the engaged volume of material/earth can be sensed using sensors (e. g. geophone or accelerometer), whereby the vibrating device can be set at the desired oscillation frequency so that the stamping plate or piles/tongues can be given an optimal vibration frequency or that the pile earth system is given oscillation properties lying at the desired value as regards the oscillation properties of the engaged volume of material.

The spring device may naturally be of any shape or design. The spring device may, for instance, be arranged to give the mass a linear to-and-fro movement with or without rotation about the axis of the movement. If, for instance, the mass is ring-shaped and surrounds the pile, tongue or the like, or if the pile is tubular and the mass is received in the cavity, the spring device may include spring arms extending into the mass and the element, with such orientation that they acquire a relative rotary movement about an axis that is parallel to the direction of movement of the striking device. In that case the spring arms may generally lie in a cylindrical surface and form a substantial angle to an axial plane to the direction of the vibratory movement (stroke direction of the striking device).

The invention will be described in the following by way of example with reference to the accompanying drawings.

Figure 1 shows a vertical section through a device for ground compacting in accordance with the invention.

Figure 2 shows schematically a vertical section through a pile driving device in accordance with the invention.

Figure 3 illustrates a pile driving device where hammer strokes are applied on a mass supported by the pile via springs and placed inside the tubular pile.

Figure 4 shows a device corresponding to that in Figure 3 but with the pile surrounded by the mass (es).

Figure 5 shows a device for supplying oscillation energy to the mass of the vibrating device with the aid of a vibrator carrier thereby.

Figure 6 shows a device as shown in Figure 1 with the addition of members to pre-stress the springs of the vibrating device.

Figures 7,8 show modified devices in which a vibrator stand carrying the vibrating members is directly supported by a vibrator attached on a pile or on a compacting plate.

Figure 9 shows another embodiment of a device in accordance with the invention.

Figure 1 shows a drop hammer 1 arranged to transmit an impulse with high energy content to a central area of a plate 4 resting on the surface of an area of soil 5. Passive vibrators are arranged on peripheral parts of the upper side of the plate 4. These passive vibrators comprise an inertial mass 2 supported on the plate 4 via springs 3.

The forces transmitted by the plate 4 to the earth material will engage an earth volume 5. The oscillatory movement of the ground/earth volume 5 engaged can be registered by a sensor 7. The oscillatory movement of the passive vibrators can be registered by sensors 6. By varying the size of the masses 2 and/or the springs 3, the natural frequency of the resonance frequency of the plate can be adjusted to suit the natural frequency of the ground volume 5 engaged.

By means of the invention the applied oscillation can be brought to correspond to the natural frequency of the system (or an overtone of the natural frequency, or some other desired vibration frequency) so that a strong amplification of the vibration is achieved. This is normally an undesired state which is controlled by suppression. However, in the present invention the resonance effect is utilized to increase the amplitude of oscillation of the object in question (stamping plate or pile/tongue) and to prolong the duration of the oscillatory movement. This means that a system can be set in motion in a prolonged oscillatory movement within the desired frequency range with the aid of a brief impulse (e. g. a hammer or a vibrator). The principle can be used, for instance, to increase efficiency during driving and removal of piles and tongues, vibration thereof and when packing earth.

In the embodiment shown in Figure 2 a pile 4 is driven directly into an earth stratum by a sledge hammer 1. The pile 4 is surrounded by a mass 2 (or by mass units) attached to the pile 4 via spring elements 3 so that the mass (es) 2 can move in relation to'the pile 4 in its axial direction. As shown in Figure 2, sensors can be attached to the passive vibrator 6, or on the pile 7, to give the passive vibrator 2,3 a desired oscillatory frequency (or an overtone thereof) corresponding to the natural frequency of the object being struck (or some other suitable frequency, e. g. an overtone of the natural frequency) to permit the pile 4 to effectively penetrate the ground 5. In certain cases, furthermore, when the earth 5 is non-cohesive earth, for instance, the natural frequency of the system can be lowered in the final hammering stage, in order to produce a packing effect in the earth material 5 surrounding the pile 4. During earth packing it may be advisable to use a suitably shaped packing device.

The invention is naturally not limited to only the embodiment or its use in the area of foundation laying but can in principle be used for driving rigid objects into other materials or for compacting all types of material.

Pronounced features of the invention are the efficient amplification of the energy applied by means of the hammering system, which results in saving energy and thus long useful life.

By way of illustration it may be mentioned that for conventional pile driving or earth packing various machines must be used for striking or vibration. No equipment exists which in a simple and efficient manner can combine striking and vibration. A drop hammer can have a mass of between 4 and 20 tons and a drop of 1-5 m. The drop hammer transmits the stroke energy as a brief impulse to the pile. In the case of vibration the pile is subjected to an oscillating vibrating movement produced by rotating eccentric masses. These can produce a centrifugal force of between ca. 500 and 2000 kN and operate with a vibration frequency in the range of 15-40 Hz. To increase penetration during vibration it would be desirable to be able to vibrate at considerably higher frequencies, between 80 and 100 Hz, corresponding to the natural frequency of the pile. At such high oscillation frequencies the energy losses and thus the wear are extremely high in an active vibrating system.

According to the present invention the resonance frequency of the vibrating device is preferably set to substantially coincide with the natural frequency of the oscillating system, or an overtone thereof, i. e. to lie at a frequency distance of zero therefrom, or at a frequency distance therefrom which gives the desired amplification effects. Such amplification effects are achieved within a certain frequency interval so that it is thus possible to choose the amplification effect or obtain a certain amplification effect even if the vibrating device does not operate exactly at the natural frequency of the oscillating system (or an overtone thereof).

In the embodiment with driving (or removal) of a pile, the inertial mass is shown placed around the pile on the outside thereof. However, it should be clear that if the pile is tubular the inertial mass can be placed in the cavity of the element. In that case the arrangement should be such that the elongate element is not subjected to any major bending buckling forces.

Figure 3 illustrates how the hammer 1 strikes the mass 2 inside the hollow pile 4. Once again the mass 2 is supported by the pile 4 via spring devices 3.

Figure 4 shows a variant of the object shown in Figure 3, wherein the mass (es) 2 is/are arranged around and outside the pile 4. The sledge hammer 1 is provided with a stamping plate 11 by which the strokes of the hammer are simultaneously transmitted to the masses 2 via protective elements 12 on the masses 2. If the mass 2 is ring-shaped the stamping plate 11 may naturally also be ring-shaped, as also the protective element 12.

Figure 5 illustrates an embodiment similar to the object in Figure 1 but in which the vibration energy is not supplied via a sledge hammer but via a vibrator 100. The vibrator 100 is supported by the mass 2 of the vibrating device and comprises a stand 104 provided with two eccentric masses 105 which rotate about parallel axes, in opposite directions, and preferably at the same speed. The vibrator 100 is arranged to produce a vibration which sets the mass 2 in motion towards and away from the compacting plate 4.

The vibration frequency of the vibrating device can be set by a suitable choice of the oscillatory frequency of the vibrator 100.

The vibrator stand 104 supports a stabilizing mass 107 via a suppressor 106. Since the vibrator 100 acts directly on the mass 2 of the vibrating device, which is supported from the packing plate 4 via springs 3, the embodiment according to Figure 5 can emit high packing energy with a relatively small vibrator 100, in accordance with the discussion above.

Figure 6 illustrates an embodiment based on that according to Figure 1 but which is supplemented in order to offer pre-stressing of the springs 3 supporting the mass 2. Figure 6 illustrates two different embodiments of pre-stressing members.

On the left-hand side of Figure 1 a tensioning rod 201 is shown, secured in the mass 4 by an attachment device 207. The rod 201 extends through an opening in the mass 2 in the direction of movement of the vibration. The upper end of the rod 201 is provided with a nut 206 cooperating with threading on the upper end of the tensioning rod 201.

The springs 3 can be compressed by the mass 2 being pressed down towards the plate 4 by some suitable equipment available at the work site, such as by loading it with a drop weight, after which the nut 206 is applied to maintain compression of the springs 3 when the weight is removed from the mass 2.

Locking devices 209 are shown on the plate 4. Each locking device 209 comprises a lever 206, the lower end of which is swivel-journalled on the plate 4 via a swivel bearing 203. At the lower end of the lever 206 is a flange 204 extending in beneath the lower surface of a drop weight 1. The upper end of the lever 206 is provided with an angled end portion 208.

When the lever 206 inclines somewhat outwards from a normal to the surface of the plate 4 through the bearing 203, the portion 208 of the arm grasps the inner edge of the mass 2. The nuts 212 can be removed so that the compression of the springs 3 is maintained by the locking devices 209.

The packing unit can now be placed on the surface of the relevant ground area 5, with pre-stressed springs 3. The sledge hammer 1 can now be dropped centrally towards the plate 4 in order to transmit its striking energy thereto, whereupon the drop weight 1 simultaneously releases the locking devices 209 thereby releasing the pre-stressing energy in the springs 3 so that the mass is set in oscillatory movement in relation to the plate 4. Thrust energy from the drop weight 1, as well as reflected energy from the ground volume 5, is returned via the springs 3 to the mass 2.

The right-hand side of Figure 6 shows another way of pre-stressing the springs 3 with the aid of wires 210 extending, for instance, through an opening in the mass 2 to and around a return roller 211 on the plate 4 and from there up to the mass 2 to which it is anchored, the wire 210 extending for instance up through an opening in the mass 2 and being joined to a load-distributing plate 212 resting on the upper surface of the mass 2. A tensile force 213 in the wire 210 can be established with the aid of the hoisting means used to raise the drop weight 1 before its next stroke.

Figures 7 and 8 show the earth mass 5 where the pile and plate 4, respectively, support the vibrator stand 301 which is connected via the springs 3 to the inertial masses 2. The stand 301 also supports an additional mass 302 via suppressors 303. The vibrators 300 are excited by rotating eccentric weights 304.

Figure 9 shows a frame 401 resting on out-of-round wheels 402 running on the surface of the ground 5. A driving means, e. g. a vehicle 403 such as a tractor, is shown drawing the frame 401 via a drawbar 404. The frame supports a compacting plate 405 in contact and parallel with the ground surface 5. The frame 401 supports an inertial mass 2 via springs 3 enabling vertical oscillatory movement. When the tractor 406 pulls the packing machine 400 sideways a vertical vibratory movement occurs due to the out-of-round wheels 402 in the masses 2 via the springs 3, this movement being transmitted to the packing plate 405. The vibratory movement occurs in the passive vibrator consisting of the mass 2 and springs 3, and is amplified by resonance effects in the manner described above. The vibratory movement is transmitted via the frame 401 to the packing plate 405 which is in contact with the earth mass 5 below, at least when the frame 401 and plate 405 assume their lowermost position as the wheels 402 turn. The frequency of the packing system is adjustable by altering the dynamic characteristic of the springs 3 and the masses. The radially projecting parts of the wheels 402 have relatively restricted carrying capacity and penetrate into the foundation 5. However, as the wheels continue to rotate the wheel parts following in circumferential direction can raise the trolley/frame.

The plate 405 is preferably arranged to be vertically adjustable in relation to the wheels 402 for adjustment to ground of varying carrying capacity.

The geometrical shape of the wheels 402 is not restricted to the shape illustrated and may be triangular, for instance, hexagonal or be in the form of a hand wheel or some other shape giving the wheels a vertical vibratory movement as they roll along a surface.

The wheels 402 may be connected together or steered so as to give synchronous, uniform vertical displacement movements.