SILENCER FOR SILENCING PILE DRIVING INTO THE BED OF A BODY OF WATER, AND PILE DRIVING SYSTEM AND METHOD

SILENCER FOR SILENCING PILE DRIVING INTO THE BED OF A BODY OF WATER, AND PILE DRIVING SYSTEM AND METHOD

TECHNICAL FIELD

The present invention relates to a silencer for silencing pile driving into the bed of a body of water.

BACKGROUND ART

Driving piles into the bed of a body of water produces a high level of noise in the surrounding environment. The noise increases alongside an increase in the diameter of the piles and in the depth of the bed of the body of water, to the point of exceeding the threshold tolerated by Cetacea and Pinnipedia. For this reason, some countries have imposed a maximum noise threshold. For example, the threshold imposed by the German government is 160 dB re lpPa at a distance of 750 metres .

One way of reducing noise is to use a contact damper between the free end of the pile and the pile driver. That is, the contact damper acts as a shock- absorber, which reduces the force of impact and, with it, the noise level by roughly 5-10 dB . Using this solution, however, more blows are needed to drive in the pile .

Another way of reducing noise is to alter the operating parameters of the pile driver and, more specifically, to prolong the time the pile driver ram remains in contact with the pile, so as to reduce vibration of, and the noise produced by, the pile. This solution, however, also has the drawback of requiring more blows to drive in the pile.

Another pile driving noise abatement solution currently being researched is to generate air bubbles around the pile.

A few examples of noise abatement techniques are described in documents US 2002080681, US 2011031062, US 2013001010, DE 10302219 and DE 10117109.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a simple, easy-to-use silencer that is highly effective in reducing noise produced by driving piles into the bed of a body of water.

According to the present invention, there is provided a silencer for silencing pile driving into the bed of a body of water, the silencer being designed to fit around a pile, and comprising a first tube longer than the depth of the bed of the body of water; a second tube, which is inserted inside and spaced apart from the first tube, and is longer than the depth of the bed of the body of water; and a bottom wall, which is joined hermetically to the first and second tube to form a gap between the first and second tube, and is designed to rest on the bed of the body of water.

This way, the silencer forms, in a straightforward, practical manner, an air gap between the noise source - the pile - and the surrounding marine environment. Moreover, sheathing the pile with the silencer, i.e. fitting the silencer fairly accurately around the pile, allows the silencer to support the pile in an upright position or, vice versa, the pile to support the silencer. The silencer and the pile are connected to each other accurately enough to ensure mutual support and alignment, while at the same time allowing the pile to slide with respect to the silencer.

Preferably, the first and second tube each have a circular cross section; the first and second tube being concentric with each other.

This way, the gap is of constant thickness in all radial, potential noise-propagating directions.

In a preferred embodiment, the silencer comprises elastic spacers between the first and second tube. The elastic spacers maintain a constant thickness of the gap. And the elasticity of the spacers dampens vibration transmission between the first and second tube. Construction-wise, each spacer preferably comprises a block of elastomer material.

In another preferred embodiment of the present invention, the silencer comprises further elastic spacers projecting radially inwards of the second tube to prevent direct contact between the pile and the second tube.

This provides for maintaining a constant distance and damping vibration transmission between the pile and the second tube, and allows mutual support of the pile and the silencer. In this case, too, each spacer comprises a block of elastomer material.

Preferably, the bottom wall is annular, with a centre opening for passage of the pile.

In a preferred embodiment of the present invention, the bottom wall projects radially beyond the second tube .

The bottom wall thus provides a relatively ample supporting area for greater stability.

Preferably, the silencer comprises at least one ballast member located on the bottom wall; the ballast member preferably being located on top of the projecting portion of the bottom wall.

This ensures greater stability of the silencer.

Construction-wise, the first and second tube and the bottom wall are made of metal.

Preferably, the silencer has an open top end from which to release sound waves from the gap.

This provides for further reducing vibration between the first and second tube. A further object of the present invention is to provide a pile-driving system designed to eliminate the drawbacks of the known art.

According to the present invention, there is provided a system for driving piles into the bed of a body of water, the system comprising a pile driving machine; and at least one silencer of the type described above .

One silencer employed together with the pile driving machine can thus be used for a plurality of piles .

In fact, the pile and the silencer, when placed around the pile, substantially define an elongated structure, in which the pile slides with respect to the silencer along the pile axis, and the silencer rests on the bed.

A further object of the present invention is to provide a method of driving piles into the bed of a body of water, designed to eliminate the drawbacks of the known art .

According to the present invention, there is provided a method of driving piles into the bed of a body of water, the method comprising the steps of resting a silencer, having at least one of the characteristics described above, on the bed of a body of water; resting a pile on the bed of the body of water and inside the silencer; and driving the pile a predetermined depth into the bed of the body of water.

Preferably, the method comprises withdrawing the silencer from the pile.

In a preferred embodiment of the present invention, the method comprises supporting the silencer by means of the pile located inside the silencer.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the attached drawings, in which :

Figure 1 shows a view in perspective, with parts removed for clarity, of a silencer in accordance with the present invention;

Figure 2 shows a partly sectioned view in perspective, with parts removed for clarity, of the Figure 1 silencer;

Figure 3 shows a larger-scale longitudinal section, with parts removed for clarity, of the Figure 1 silencer;

Figure 4 shows a cross section, with parts removed for clarity, of the Figure 1 silencer along line IV-IV in Figure 3;

Figure 5 shows a larger-scale view in perspective, with parts removed for clarity, of a detail of the Figure 1 silencer; Figures 6 and 7 show partly sectioned elevations, with parts removed for clarity, of successive pile driving stages.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in Figures 1 and 2 indicates a silencer. Silencer 1 is positioned resting on the bed 2 of a body of water 3 to prevent or reduce the propagation of sound waves into the body of water 3 when driving piles 4 into bed 2 of body of water 3. Silencer 1 is fitted about pile 4, and is longer than the depth of bed 2 of body of water 3.

Piles 4 are normally foundation piles of such a length that, even when driven into bed 2 of body of water 3, a top end of each pile projects from body of water 3.

Silencer 1 comprises a tube 5 longer than the depth of bed 2 of body of water 3; a tube 6, which is inserted inside and spaced apart from tube 5, is longer than the depth of bed 2 of body of water 3, and is designed to fit around pile 4; and a bottom wall 7, which is joined hermetically to tubes 5 and 6 to form a gap 8 between tubes 5 and 6, and is designed to rest on bed 2 of body of water 3. Gap 8 is full of air.

Silencer 1 preferably has an open top end 9 through which any sound waves inside gap 8 are expelled from body of water 3. In the example shown, tubes 5 and 6 each have a circular cross section and are substantially concentric, as shown more clearly in Figure 4.

With reference to Figure 5, silencer 1 comprises spacers 10 between tubes 5 and 6. Spacers 10 are preferably elastic and each comprise a block 11 of elastomer material, and two brackets 12 for supporting block 11. Spacers 10 are fitted to, and project radially outwards of, tube 6.

In the example shown, spacers 10 are equally spaced axially and circumferentially on the outer face of tube 6.

Silencer 1 comprises further spacers 13 along the inner face of tube 6, to keep tube 6 a given distance from pile 4.

Spacers 13 are substantially identical to spacers 10, and each comprise a block 11 of elastomer material, and two brackets 12 for supporting block 11.

Spacers 13 are fitted to, and project radially inwards of, tube 6.

In the example shown, spacers 13 are equally spaced axially and circumferentially on the inner face of tube 6.

With reference to Figure 3, bottom wall 7 is annular with a central opening 14 for passage of pile 4. Bottom wall 7 projects radially beyond tube 6. The projecting part of bottom wall 7 is connected to tube 6 by reinforcing brackets 15. In actual use, bottom wall 7 is positioned resting on bed 2, and the projecting part of bottom wall 7 may be used to house ballast 16 as shown in Figures 6 and 7.

Tubes 5 and 6 and bottom wall 7 are generally made of metal .

With reference to Figures 6 and 7, silencer 1 forms part of a system for driving piles 4 into the bed 2 of a body of water 3. The system comprises a pile driving machine 17, and at least one silencer 1.

Silencer 1 is supported by pile 4.

In actual use, pile driving into the bed 2 of a body of water 3 comprises resting a silencer 1 on bed 2 of body of water 3; resting a pile 4 on bed 2 of body of water 3 and inside silencer 1; and driving pile 4 a predetermined depth into bed 2 of body of water 3.

Silencer 1 is then recouped by removing it from pile 4 supporting it.

In addition to effectively damping sound waves emitted when driving pile 4, silencer 1 actually also serves as a sort of coupling enabling axial slide of pile 4, and supports pile 4 in a vertical position. Conversely, pile 4, if otherwise supported, may effectively support silencer 1.

Clearly, changes may be made to the embodiment described of the present invention without, however, departing from the protective scope of the accompanying Claims .