The use of piling as a method to provide foundation support for buildings and constructions has become more common in recent years, because land for building sites in the vicinity of large cities is becoming sparse, and piles to be embedded in the soil can be used to provide a rigid foundation even in such areas where construction would otherwise not be possible because of the low load bearing capacity of the soil. The development and improved efficiency of pile driving machines used for embedding piles, as well as e.g. the resulting reduction in the costs of piling has also made foundations based on piling more advantageous and thereby more competitive with respect to alternative approaches to foundation. One factor limiting the application of piling has conventionally been the fact that the driving of piles by hammering into the soil causes relatively high noise which can be found disturbing in the immediate surroundings (for example, in a residential neighbourhood). In studies on noise caused by drive piling machines, the sound has been found to be generated in the hammer of the drive piling machine when the massive movable part or ram moving back and forth in connection with the body of the hammer hits a pile cap inside a housing for the pile cap in the lower part of the body and on the pile. In pile driving machines of prior art, the noise level may rise above 100 dB in the vicinity of the pile driving machine during hammering of the pile into the soil. This drawback has limited the application of piling particularly in areas where the harm caused by the noise is great, for example in densely populated neighbourhoods. Naturally, the high noise generated during the operation of the pile driving machine is also harmful to the operators of the pile driving machine and other persons working on the building site in question. At present, attempts are made to suppress the noise generated in known pile driving machines for example by placing the hammer and the pile to be hammered into the soil, inside a separate sound absorbing protective shell. However, such a noise suppression solution, as presented for example in JP04343912 A2, is relatively complex and expensive. Furthermore, it will complicate the pile driving process as such, because the piles must always be placed within a protective shell having a height which is at least equal to their own height, before the actual pile driving is started. Furthermore, such a noise suppression solution, implemented with a protective shell outside the hammer and the pile, prevents the visual monitoring of the behaviour of the pile during the hammering.

Attempts have also been made to suppress the noise generated in the hammer by other methods, such as encapsulation, suppressing coatings, and a pile cap housing suppressed with sand. Furthermore, for example publication JP62017225 discloses a solution, in which the noise and vibration caused by the impacts of the ram are suppressed by providing the ram with a hollow section containing granular filler material with suitable properties. This material is struck against the bottom of the hollow section slightly after the ram has collided against the pile cap. In this way, it prevents the ram from bouncing up right after the impact (by a repulsion force) and thereby suppresses vibration and noise generated by the impacts. Publication JP 1268917, in turn, presents a solution, in which the top of a pile and the face of a ram on the pile side are equipped with electromagnets. In this solution, the electromagnets are supplied with electric current to provide magnetism of the same pole in the electromagnets right before contact of the ram with the head of the pile. The strong magnetic fields generated prevent the mechanical contact between them, which suppresses the noise caused by the impacts of the ram. However, these suppression solutions have not become common either, apparently because the sound suppression achieved by them has been relatively insignificant, and later studies have shown that a major part of the noise is caused, among other things, by the wobbling of the ram after the impact. Brief summary of the invention

It is an aim of the invention to produce a novel hammer for a pile driving machine, to eliminate the above-mentioned drawbacks relating to hammers of prior art for pile driving machines, and to noise suppressing solutions used in them. In particular, it is an aim of the invention to introduce a hammer for a pile driving machine, whereby the hammer can be made quieter than a non- suppressed hammer without compromising the other properties and usability of the non-suppressed hammer. Furthermore, it is an aim of the invention to introduce such a novel noise suppression solution implemented in a hammer for a pile driving machine, which does not require major changes in the basic structure of the hammer or separate supplementary parts affecting the pile driving process or the structure or operation of the pile driving machine. The inventive idea of the hammer for a pile driving machine according to the invention is to prevent vibration originating from the ram that hits the pile cap inside the housing for the pile cap and from the pile cap itself during and after an impact, from being transferred to the outer walls of the body by means of sound suppressing material layers placed between at least the ram and the body of the hammer, as well as between the pile cap and the side walls of the housing of the pile cap, wherein the volume of the noise generated in the outer walls of the housing for the pile cap decreases. One principle in the invention is also the fact that the aim is to suppress noise mostly in the mid- range in which the human ear is most sensitive, by selecting the material and the dimensions of the noise suppressing material layers in such a way that their suppressing capacity is greatest exactly in this frequency range. To put it more precisely, the hammer for a pile driving machine according to the invention is characterized in what will be presented in the claims. By hammering reinforced concrete piles into the soil by means of a hammer for a pile driving machine according to the invention, based on the above described principles, significantly lower noise levels have been achieved than by using corresponding non-suppressed hammers, without significantly changing the structure, the operation or the usability of the hammer itself or of the pile driving machine. In noise measurements taken on a pile driving machine equipped with a hammer according to the invention, the sound pressure of the noise spreading from the body of the hammer to the environment decreased by a total of about 10 to 15 dB, when the effects of the sound suppressing structure of the joint between the housing of the pile cap and the body, and the walls of the body of the hammer which are more solid in the solution of the invention than in prior art, are also taken into account. Thanks to the decrease in the level of these sound pressures, the hammer according to the invention makes it possible to achieve a sound pressure level of even lower than 80 dB. This means, in principle, a noise volume that is already so low that the wearing of hearing protectors would no longer be obligatory, according to the occupational safety regulations, for persons working with the pile driving machine or in its vicinity.

Description of the drawings

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows an embodiment of a hammer for a pile driving machine

according to the invention, in a side view,

Fig. 2 shows the cross-section A-A of the hammer shown in Fig. 1 ,

Fig. 3 shows the cross-section B-B of the hammer shown in Fig. 1 , and

Fig. 4 shows the cross-section C-C in the longitudinal direction of the hammer shown in Fig. 1.

Detailed description of the invention

The hammer for a pile driving machine shown in Figs. 1 to 4 is a hydraulically driven hammer which is moved along guides on the outer surface of the frame of the pile driving machine in a way known as such, for example by means of cable wires or chains. In such a hammer, the impact energy to be directed to the head of the pile is produced by moving a ram movable inside the hammer by means of gravity and the pressure of hydraulic fluid. The external parts of the hammer consist of a frame 1 , whose upper part comprises a ram space 3 surrounded by an outer wall 2, and whose lower part comprises a pile cap housing 4. Inside the ram space 3, there is a ram 6 that moves back and forth along guides 5 and hits the pile cap 7 inside the pile cap housing 4 underneath the ram space, when the pile is hammered into the soil. The reciprocating movement of the ram 6 is driven by a double- acting hydraulic cylinder (not shown in the figures) in the upper part of the frame 1. The hydraulic fluid required for the cylinder is normally supplied to it by means of a hydraulic aggregate in connection with the pile driving machine. These apparatuses which take care of the reciprocating movement of the ram 6 in the ram space 3 inside the frame 1 of the hammer are known as such with respect to their structure and operating principle, so that their structure and operation will not be described in more detail in this context.

In this embodiment, the cross-section of the ram space 3 is almost rectangular, as shown in Fig. 3. The outer walls 2 of the ram space 3 have been shaped to be curved slightly outwards, to leave a sufficient air space between the ram 6 and the outer walls 2, to enable a flow of air in the ram space 3 for cooling the ram 6 and the pile cap 7 inside the housing for the pile cap during the hammering of the pile.

The guides 5 inside the ram space 3 are fastened to the inner corners of the outer wall 2 of the frame 1. In this application, the fastening has been imple- mented by means of covering pieces 9 fixed on top of openings 8 formed in the corners from the outside. Special-purpose vibroinsulators 10 have been installed between the covering pieces 9 and the guides 5 to suppress vibrations transferred from the ram 6 via the guides 5 and the covering pieces 9 to the outer walls 2. In this embodiment, the vibroinsulators 10 are made of polyurethane or another suitable material which is resilient but which, thanks to its solidity, is also a material that efficiently suppresses vibrations. In the lower part of the ram space 3, a bottom flange 11 is provided, having an opening 12 at the centre, through which the lower part of the ram 6 extends into the pile cap housing 4 underneath the ram space 3 when the ram 6 moves towards the bottom dead centre of its movement, that is, the point where it impacts against the pile cap 7 inside the pile cap housing 4. The outer wall 2 of the frame 1 , surrounding the ram space 3, is in this embodiment made as closed as possible, so that the sound generated by the vibration of the ram 6 itself inside the ram space 3 could not escape directly from the ram space 3 to the outside of the frame 1. In the upper and lower parts of the ram space 3, however, the outer wall 2 is provided with special flow openings 13a and 13b for guiding the air flows caused by the movements of the ram 6 from the outside of the hammer into the ram space 3 and out again, because otherwise the pressure variation caused by the movements of the ram 6 would slow down the speed of the reciprocal movement of the ram 6 and thereby cause power losses retarding the pile driving process. To prevent the escape of sound vibrations generated in the ram space 3 via these flow openings 13a and 13b, they are provided with special flap valves 14a and 14b made of rubber or another suitable resilient material. They allow the air to flow in and out according to the movements of the ram 6 but reduce significantly the way of sound vibrations out of the ram space 3 to the outside of the hammer.

The function of the pile cap housing 4 in the lower part of the frame 1 is, among other things, to fit the hammer to match piles of different sizes and to suppress concussions caused by impacts of the ram 6 in a suitable way so that the pile against it is not damaged by the impacts of the ram 6. The structure of the pile cap housing 4 is best shown in Figs. 2 and 4. At its end on the side of the ram space 3, a cover flange 15 is provided, by means of which the pile cap housing 4 is connected to a bottom flange 11 in the lower part of the ram space 3 by means of connecting screws 16 installed in fastening holes in these flanges. In this embodiment, a material layer 17 for suppressing vibration is also provided between the bottom flange 11 of the ram space 3 and the cover flange 15 of the housing for the pile cap. Its function is to prevent the propagation of vibration generated by the impacts in the pile cap housing 4, from the housing 4 to the outer wall 2 of the frame 1.

An improvement that has the greatest effect on the noise generated in the pile cap housing 4 has been achieved by making the side wall 18 of the pile cap housing 4 suppress vibration in such a way that the vibrations caused by impacts on the pile cap 7 are significantly suppressed before they can propagate to the outer surface of the side wall 18 of the pile cap housing 4, where they generate acoustic waves which spread into the environment and are, in practice, heard as harmful noise. To achieve this, as shown in Fig. 2, the side wall 18 of the pile cap housing 4, which in this case has a circular cross section, is formed of an inner jacket 19 and an outer jacket 20 as well as a vibration suppressing material layer 21 installed between them.

The vibration suppressing material layer 21 on the side wall 18 of the pile cap housing 4 is, in this case, also made of polyurethane. The material of the inner jacket 19 and the outer jacket 20 is, in this case, steel. The outer jacket 20 is connected to the cover flange 15 (e.g. by welding), and the sound suppressing material layer made of polyurethane or another suitable material, as well as the inner jacket, are then installed inside the outer jacket 20. In this case, a special gasket flange 22 is fastened onto the inner jacket, a central opening 23 in the flange being slightly smaller than the openings in the centre of the bottom flange of the cover flange 15 and the bottom flange of the ram space 3 and corresponding, in its inner dimensions, more closely to the outer diameters of the end of the ram 6, wherein the space between, the ram space 3 and the inner space of the sound suppressing piece is tighter and thereby better sound insulating than before. The outer jacket 20 is, in this case, slightly longer in its lower part than the inner jacket, so that the sound insulated part of the pile cap housing 4 extends, in this embodiment, only to the upper part of the pile cap 7, as shown in Fig. 4. The part underneath the inner jacket 19 is provided with flow openings 28 to allow the flow of air around the pile cap 7 during impacts. The flow openings 28 can also be equipped with flap valves made of rubber or a similar material, like those in the flow openings 13a and 13b.

Furthermore, an end piece 25 is provided underneath the side wall 18. It is fastened to a lower flange 24 fixed to the lower edge of the outer jacket 20 in a detachable manner by fastening screws 30 fitted via fastening holes (not shown) in the jacket and in the fastening flange 26 of the end piece, forming the upper edge of the end piece 25. At the lower end of the end piece 25, a conical fitting opening 27 is provided, from which the pile to be hammered into the soil is fitted into a recess 31 in the lower part of the pile cap 7. For suppressing sounds generated between the upper head of the pile and the recess 31 in the pile cap, a gasket flange 29 made of rubber or another resilient material is installed at the inner edge of the conical part of the fitting opening. The opening in the centre of the gasket flange 29 is dimensioned according to the outer dimensions of the pile in such a way that as few empty spaces as possible are left between the fitting opening 27 and the pile, from which spaces the sounds generated in the recess 31 could come out of the end piece 25.

When piles are hammered into the soil by the hammer shown in Figs. 1 to 4, the ram 6 in the ram space 3 inside the frame 1 of the hammer moves back and forth, up and down, and when in the lowermost point, the end of the ram impacts against the pile cap 7 inside the pile cap housing 4 in a way known as such. As a result, vibration is caused that proceeds to the outer walls 2 of the ram space 3 and is heard outside the hammer as a hammering sound at a frequency corresponding to the stroke frequency. In the hammer shown in Figs. 1 to 4, the vibration of the ram 6 is, however, significantly suppressed with respect to unsuppressed hammers of prior art, because the guides 5 of the ram 6 are connected to the outer wall 2 by means of the vibration- suppressing vibroinsulators 10. Also, the pile cap 7 inside the pile cap housing 4 normally causes part of this noise. In the embodiment shown in Figs. 1 to 4, vibration caused by deformations of the pile cap 7 proceeds to the inner jacket 19 of the side wall 18. Thanks to the vibration suppressing material layer 21 between the inner jacket 19 and the outer jacket 20, as well as the vibration suppressing material layer 17 between the cover flange 15 and the bottom flange 11 of the ram space 3, significantly less vibration can proceed to the outer jacket 20 of the side wall 18 and elsewhere in the frame 1 of the hammer than previously. As a result, the sound pressure of the noise generated in the outer surfaces of the frame 1 remains lower than in unsuppressed hammers. The volume of the noise is also reduced by the fact that there is no free air connection from the ram space 3 and from the inside of the housing for the pile cap to the ram 6 and to the pile cap 7. As mentioned above, with these relatively slight changes with respect to the prior art, it has been possible to reduce the sound pressure of noise generated by the hammer by a total of about 10 to 15 dB. Most of this reduction in the noise is caused by the vibroinsulators of the guides 5 in the ram space 3 as well as the vibration suppressing material layer between the inner jacket 19 and the outer jacket 20 of the side wall 18 of the housing for the pile cap. Furthermore, part of this reduction in the volume of the noise has been found to be achieved with sealed structures of the outer wall 2 and the end piece 25 of the pile cap housing 4, on the basis of measurements taken in connection with test impacts with the hammer according to the invention.

In many respects, the hammer according to the invention can be implemented in a way different from the above-described example embodiment. For example, in lieu of polyurethane, other vibration suppressing materials can also be used as the material for suppressing vibration. Naturally, e.g. the thickness of these vibration suppressing material layers can also be varied. In the embodiment shown in Figs. 1 to 4, their thickness is normally 5 to 10 mm. Naturally, when different materials are used, the suppressing proper- ties of the material may affect the required thicknesses of the material layers. However, in view of an excessive increase in the outer dimensions of the hammer, thinner material layers are more advantageous than thicker ones. On the other hand, when suppressing vibrations, the specific frequejTcles,Qf- the system should also be taken into account. In the embodiments of Figs. 1 to 4, for example the vibration suppressing materials of the guides 5 of the ram 6 as well as the suppressing materials of the inner jacket 19 and the outer jacket 20 of the side wall 18 of the pile cap housing 4 act in such a way that vibration strengthening resonance frequencies do not fall in the mid- range of human hearing, that is, the range in which the human ear is most sensitive. This has been determined by measurements on noise and vibration for the hammer according to the invention. Furthermore, in noise measurements taken on hammers, it was also found that noise coming with air flowing out of the inner parts of the ram space 3 in the upper part of the frame 1 of the hammer and the housing 4 of the pile cap, directly to the outside of the hammer, can be reduced by a more sealed structure of these parts. However, when increasing the sealing, one should note that the ram 6 moving inside the ram space 3 and the pile cap 7 inside the pile cap housing 4 tend to be heated during the hammering of the pile, because of mechanical energy consumed in deformations of the pile cap 7. As a result, sufficient air should circulate and be renewed inside the housing for the pile cap and in the ram space in such a way that the temperature of the ram and the pile cap would remain reasonable even during long series of impacts. As an alternative for the flap valves used in the embodiment of Figs. 1 to 4, it would also be possible to use other sound absorbing valves. These might include, for example, valves equipped with sound traps or other sound dampers. Also in other respects, the above invention should not be limited to the above described example embodiments, but the invention can be implemented in many different ways deviating from them, within the scope of the inventive idea defined in the following claims.