The invention relates to a transport means, such as a vessel or vehicle, provided with a device for compacting ground, said compacting device being provided with a pile with a baseplate and with guides arranged on the transport means for guiding the pile in a direction towards and away from the ground.

A vessel with a compacting device is used for impact compacting a bed. The bed thus compacted can for instance serve as natural foundation bed for a bridge or a quay construction in which, if necessary, further work to the bed can be carried out. In this known vessel, the pile and the baseplate are rigidly attached to each other and form the compacting weight. Since the pile is guided by the guides on the vessel, a good positioning of the pile can be realized relative to the bed to be compacted. Although a uniformly compacted bed can thus be realized, practice has shown that in many cases the bed can only be compacted up to a small depth. Since in some applications the bed needs to be compacted up to greater depths, ten metres or more, such a vessel is not suitable for carrying out such a desired compaction.

It is an object of the present invention to provide a vessel with a device for compacting a bed, by which a bed can be compacted up to great depth, while maintaining a uniform compaction.

For this purpose, a transport means of the sort mentioned

in the preamble is characterized according to the inven¬ tion in that the baseplate is attached to the pile in an axially movable manner. The invention is based on the insight that in impact compacting the maximum compacting force and the energy exchange time within which the energy is transferred from the compaction weight to the bed play an important role. When the baseplate is rigidly attached to the pile, the energy exchange time has been found to be relatively long and the maximum compacting force relatively small. This can be explained in that the pile with the baseplate bounces when it strikes the bed. The result of this is a relatively shallow compaction. By now, according to the invention, mechanically disengaging to a great extent the baseplate from the pile, or in other words by attaching the baseplate to the pile in an axially movable manner, a relatively short energy-exchange time and a relatively great compacting force is obtained, which results in a compaction up to a great depth, of 10 metres or more. The compacting device according to the invention can also be used on a different conveying means, such as a vehicle.

A preferred embodiment of a transport means according to the invention is characterized in that the baseplate is attached to the pile by means of a line, such as a chain or a cable. Owing to this, a simple yet efficient suspen¬ sion of the baseplate to the pile is obtained.

A further preferred embodiment of a transport means accor- ding to the invention is characterized in that the baseplate is attached to the pile by means of a spring element. By connection to a spring element, depending on the type of ground to be compacted, such a dynamic operating condition can be given to the pile-baseplate system that as a result, among other things, the desired compacting depth can be adjusted.

When a transport means according to the invention is provided with a tensioning device for adjusting the pre¬ tension of the spring element, a single compacting device can be used to compact various types of ground, and/or to compact ground in various ways. Thus, it has for instance been found that in ground having a top layer of granular rock such as gravel or shingle, a connection between baseplate and pile with low pre-tension does provide a compaction deep down in the ground but not in the top layer. By increasing the pre-tension, such dynamics can be given to the baseplate-pile structure, that the top layer is compacted.

When the baseplate is detachably attached to the pile, replacing the baseplate for repairs or adjustment to the type of bed to be compacted can be carried out in a very simple manner. It has further been found that a suitable mass ratio between baseplate and pile can on the one hand reduce undesired springing effects in the pile and can, on the other hand, promote the energy transmission onto the ground to be compacted.

A preferred embodiment of a transport means according to the invention is characterized in that the pile consists of several parts, the parts being attached to each other in an axially movable manner. By constructing the pile from several parts, which may differ in length, weight, section or dynamic hardness, the pile can, on the one hand, be protected against undesired deformations (caused by the flow of water, in the base of a bed, or springing effects) and, on the other hand, be adjusted to the type of ground to be compacted or to the desired compaction.

When the baseplate consists of several parts, which are to be detachably attached to each other, which parts can have different weights, the dynamic behaviour of the pile- baseplate structure can be adjusted to the dynamic

behaviour of the ground to be compacted, which promotes the uniform compaction of the ground.

A further preferred embodiment of a transport means is characterized in that sensors, such as acceleration sen¬ sors, deformation sensors and sound sensors are attached to the pile and/or baseplate. With the aid of these sen¬ sors, the maximum compacting force and the energy-exchange duration during the impact landing of baseplate and pile on the bed can be measured. These sensors render it pos¬ sible, in a few test compactions prior to the actual compacting work itself, to determine the dynamic behaviour of the ground which is to be compacted. On the basis of the readings supplied by the sensors the desired mass ratio between baseplate and pile, the mass of the baseplate and the possibly desired pre-tension can, among other things, be adjusted. During the actual compacting work, the sensors indicate the compaction realized after every compaction impact, so that accurate supervision of the compaction can be realized.

The sensors are preferably electrically connected to a control device for controlling the tensioning device to adjust the pre-tension of the spring element. In this manner, it becomes possible to obtain a desired compaction of the ground in a highly automatized manner.

An embodiment of a transport means with a compacting device according to the invention will be described by way of example on the basis of the drawing, in which a vessel is shown as an example for the application of the inven¬ tion. The following is shown in:

figure 1: a schematic side view of a vessel with compac- ting device according to the invention,

figure 2: a schematic side view, in part in section, of a

pile with a ramming plate axially movably attached thereto,

figure 3: a schematic top view of figure 2, and

figure 4 : a schematic connection of baseplate and pile by means of a spring element.

Figure 1 schematically represents a vessel provided with a device 2 for compacting a bed 3. The vessel comprises two pontoons 1 and 4, the pontoon 1 being attached to the elongated pontoon 4 which is on the side opposite the pontoon 1 secured to the bed by means of a working pile

(not shown) . The combined pontoons 1 and 4 also comprise a stepping pile, two side wires and a control device. During the compacting action, a swinging action around the working pile takes place by means of the side wires, so that a path of the bed to be compacted is covered. After each path, the stepping pile is used to step to a new path.

The compacting device 2 comprises a pile 5 which can be shifted away in the direction of the bed 3 by a hoisting device 6, the pile 5 being guided by guides 7 which are arranged on the vessel 1.

In order to compact the bed 3, the pile 5, which can for instance weigh 40 tons, is hoisted by the hoisting device 6 to a certain distance above the bed 3 and the hoisting device 6 subsequently lets the pile 5 drop freely. The guides 7 cause the pile 5 to be accurately guided towards the location of the bed 3 which is to be compacted. The pile carries a plurality of measuring sensors for measuring, among other things, the energy exchange time and the maximum compacting force exerted on the bed. With the aid of the readings, the number of times can be deter¬ mined that the pile should drop onto the bed. If the

location to be compacted is sufficiently compacted, then the vessel is shifted to such an extent by being swung around the working pile of the pontoon, that the pile is located over the next location of the bed that is to be compacted. In this way, a certain section of the bed can be uniformly compacted.

Generally, a vessel that is used to perform work on the bed comprises a working pile and a stepping pile which can be secured on the bed. By using this pile with its guides on the vessel as compacting pile, no additional guides or hoisting devices need to be arranged on the vessel. The compacting device 2 shown in figure 1 is therefore preferably formed by the stepping pile with the associated hoisting device and guides.

A baseplate 8 is attached on the free end of the pile 5, of which baseplate the active ramming surface and the mass are adapted to the type of bed and to the desired compac- tion. This adaptation is carried out on the basis of readings provided by the measuring sensors arranged on the pile, for instance by prior compaction tests. In order to avoid having to change the entire pile 5 with baseplate 8 during changing mechanical and dynamic circumstances, the baseplate 8 is preferably detachably attached to the pile 5.

According to the invention the baseplate 8 is attached to the pile 5 in such a manner, that the baseplate 8 is movable relative to the pile 5, namely in axial direction thereof. Such a mechanical loose connection between baseplate 8 and pile 5 yields a relatively great maximum compacting force during the impact landing of the pile 5 and the baseplate 8 on the bed 3, as well as a relatively short energy-exchange time, as a result of which the bed can be compacted up to a depth of ten metres or even more. The effective ramming surface of the baseplate and the

mass ratio between baseplate and pile have been found to be less decisive for the compacting depth. Adjusting the dynamic behaviour of pile-baseplate structure to the dynamic behaviour of the bed which is to be compacted, can be effected by constructing the pile and/or baseplate from several parts.

Figures 2 and 3 show an example in greater detail of a baseplate 8, which is movably attached to a pile 5. The mass and the shape of the baseplate 8 are chosen such, that a desired penetration depth during compaction can be realized. In order to be able to accurately reproduce this penetration depth, the baseplate 8 preferably comprises a sleeve-shaped part 10 which surrounds the pile 5. As a result, the pile 5 has clearance and the baseplate 8 is guided towards the location of the bed which is to be compacted. The baseplate 8 comprises a plurality of rein¬ forcing ribs 11 to give the baseplate 8 a desired stiff¬ ness.

The baseplate 8 is loosely attached to the pile 5 by means of chains 9 attached to a ring 12, which ring 12 is at¬ tached in a groove 13 of the pile 5. This is done in order to form a resiliently damping pile-ramming plate system. Apart from chains, cables or other lines can be used for the attachment.

Of the many materials from which the baseplate 8 can be manufactured, steel or concrete have been found to be extremely suitable materials.

Figure 4 shows a schematic representation of a different embodiment of a vessel according to the invention, in which the connection of the baseplate 8 to the pile 5 is realized by means of a spring element 14. This spring element 14 preferably is a spring element of which the pre-tension is adjustable by means of a tensioning device

15. With a suitable choice of the spring element 14, or a suitable adjustment of the pre-tension by the tensioning device 15, the degree of mechanical connection between the baseplate and pile can be adjusted from between an almost loose connection and an almost rigid connection. As a result, the maximum compacting force and the energy-ex¬ change time are adjustable, and so, consequently, is the compacting depth. It is therefore possible to obtain various compacting depths with a single compacting device, comprising a tensioning device and a spring element.

It has been found that when a bed with a layer of granular stone, such as gravel or shingle, is covered with a substantially loose connection between baseplate and pile, a depth compaction is indeed provided but surface com¬ paction is not. In other words, the top layer is not com¬ pacted. By using a compacting device with a suitable, less loose connection between baseplate and pile, a surface compaction is obtained without causing bed cracks in the sub-layers that have already been compacted. For this purpose, two separate compacting devices can be used, but it is preferred that a compacting device with spring element and tensioning device is used.

As was already discussed above, measuring sensors 16, 16', 17 and 18 are preferably arranged on the baseplate 8 and the pile 5. The deformation sensor 18 measures the defor¬ mations of the pile due to pressure and pulling forces during compaction and as a result of water flow. Sound sensors 16 and 16' measure the sound velocity in the baseplate-pile structure and an acceleration sensor 17 measures the acceleration effects occurring during compac¬ tion. All these measurement sensors are connected to a central processing unit which can reproduce and process the readings. These readings can be used to deduce the desired compaction for a certain type of bed or the com¬ paction that has been achieved. Depending on the desired

data, several sensors can be arranged or some can be omitted.

The measuring sensors are preferably connected via the central processing unit to a control device for control¬ ling the tensioning device for the spring element. As a result, the pre-tension is adjusted automatically in dependence on the readings and a course of the compacting process, included in the central processing unit, which a desired compaction should provide. Thus, it is possible to compact a bed covered with a layer of shingle from the surface up to a desired depth in a largely automatized manner.

Although the invention has been described on the basis of a vessel, it will be understood that the compacting device described above can also be placed on a vehicle.

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