Acoustic barrier and method of pile driving

Abstract

There is disclosed an acoustic barrier (40) for use in a pile driving method in which a pile (I0) is driven into the ground 60, the acoustic barrier (40) comprising: an acoustic dampening layer (42); and a magnetic element (36); wherein the acoustic barrier (40) is arranged to be at least partly wrapped around an axial portion of the pile (I0) so that the acoustic dampening layer (42) at least partly surrounds the axial portion of the pile (I0), and wherein the magnetic element (36) is arranged to releasably secure the acoustic barrier (40) to the pile (I0). There is also disclosed a pile driving method comprising wrapping the acoustic barrier (40) around an axial portion of a pile (I0), driving an axial length of the pile (I0) into the ground, and removing or repositioning the acoustic barrier (40). There is also disclosed an acoustic barrier for a pile driving hammer having a support frame which can be detachable attached to the hammer.

Claims

1. A method for pile driving comprising: providing an acoustic barrier comprising an acoustic dampening layer and a magnetic element, wherein the magnetic element is arranged to releasably secure the acoustic barrier to a pile; wrapping said acoustic barrier at least partly around an axial portion of the pile so that the acoustic dampening layer at least partly surrounds the axial portion of the pile; driving an axial length of the pile into the ground so that the acoustic barrier moves downwardly with the pile; and removing or repositioning the acoustic barrier; wherein the acoustic barrier is removed or repositioned when it reaches a threshold height above ground level; and wherein the method comprises repositioning the acoustic barrier to a relatively higher axial portion of the pile.

2. The method for pile driving according to claim 1, wherein the method comprises repeatedly driving an axial length of the pile into the ground and repositioning the acoustic barrier to a relatively higher axial portion of the pile.

3. The method for pile driving according to claim 1, wherein repositioning the acoustic barrier comprises sliding the acoustic barrier upwardly along the pile without removing the barrier from the pile.

Description

(1) The invention will now be described, by way of example, with reference to the following drawings in which:

(2) FIG. 1 schematically shows a hammer and pile in a pile driving operation;

(3) FIG. 2 schematically shows the hammer of FIG. 1 in exploded view;

(4) FIG. 3 schematically shows the acoustic barrier for the pile of FIG. 1 in plan and side views;

(5) FIG. 4 schematically shows the pile with the acoustic barrier partially wrapped around the pile according to an embodiment of the invention;

(6) FIG. 5 schematically shows the pile of FIG. 4 after a pile driving operation;

(7) FIG. 6 schematically shows the pile of FIG. 4 with the acoustic barrier repositioned on the pile.

(8) FIG. 7 schematically shows the pile provided with a plurality of acoustic barriers;

(9) FIG. 8 schematically shows the pile of FIG. 7 after a pile driving operation.

(10) FIG. 1 shows a pile 10 and a hammer 20 for driving the pile 10 into the ground 60. The pile 10 comprises a hollow steel tube of approximately 600 mm in diameter and 6 m in length with a wall thickness of approximately 10 mm.

(11) The hammer 20 is arranged to be held by a crane above the pile 10 by crane attachment portions 21 (FIG. 2). The hammer 20 comprises a hammer body 22, a set of vertical guide rails 24 for guiding a drop load (not shown) along the hammer body 22, and a hammer head 26 at the lower end of the hammer body 22. In use, the hammer 20 is held above the pile so that the hammer head 26 rests on the top of the pile 10, and the drop load is successively raised and dropped in a pile driving operation to drive the pile 10 into the ground.

(12) Pile driving operations typically generate high levels of noise. In order to reduce the level of noise, acoustic barriers are provided according to the invention for both the hammer 20 and the pile 10. An acoustic barrier 30 is provided for the lower end of the hammer 20, and a further acoustic barrier 40 is provided for the pile 10.

(13) As shown in FIG. 2, the acoustic barrier 30 comprises a support frame 32 having a curved profile that, viewed from above, has a semi-circular forward portion, straight sides and an open rear. The support frame 32 comprises two discrete supports 34, each forming one side and one half of the semi-circular front of the support 32. Each support 34 has attachment portions 36 for attaching to the hammer body 22 by bolt holes 28 formed in the hammer body 22. In this embodiment, the support frame 32 is configured to be retro-fitted to the hammer 20 making use of existing bolt holes 28 in the hammer body 22. The support frame 32 can be fitted to the hammer body 22 by installing each support 34 from the front and/or side of the hammer body 22.

(14) The acoustic barrier 30 for the hammer 20 further comprises an acoustic dampening layer 38 or acoustic curtain arranged to fit over the frame. In this embodiment, the acoustic dampening layer 38 comprises high tenacity polyester, although any suitable acoustic material may be used. The acoustic dampening layer 38 is flexible so that it conforms to the shape of the support frame 32 when attached thereto. The acoustic dampening layer 38 is attached to the support frame 32 by clips (not shown), but in other embodiments may be bolted to the frame 32 or coupled to the frame by any another suitable means.

(15) In other embodiments, the acoustic dampening layer 38 may be pre-formed so that it has a curved shape corresponding to that of the support frame 32 before it is installed.

(16) FIG. 3 shows the acoustic barrier 40 for the pile 10 unfurled from the pile 10 (i.e. before attachment to the pile). The acoustic barrier 40 comprises a layer of acoustic dampening material 42 approximately 2 m wide and 50 mm thick. The acoustic dampening layer 42 is sized to wrap around the pile 10 so that its lateral ends meet or face one another, taking into account the thickness of the acoustic dampening layer 42.

(17) The acoustic barrier 40 further comprises a plurality of arrays 44 of magnetic elements 46 spaced apart over one side of the acoustic dampening layer 42. In this embodiment, there are four arrays 44 laterally spaced apart on a first surface of the acoustic dampening layer 42. Each array 44 extends in an axial direction perpendicular to the lateral direction of the barrier 40, so that they are substantially parallel with the axis of the pile 10 when the barrier 40 is wrapped around the pile 10.

(18) Each array 44 comprises a plurality of magnetic elements 46 axially spaced apart and attached to the acoustic dampening layer 42. In this embodiment, there are five magnetic elements 46 in each array 44. Each magnetic element is approximately 25 mm in diameter and 5 mm thick, and has a lifting weight of approximately 7 kgs (i.e. each magnetic element is capable of lifting a ferromagnetic weight of 7 kgs, in particular a steel weight). The magnetic elements 46 can be attached to the acoustic dampening layer 42 by any suitable means, such as by an adhesive, by bolts or other fastening elements.

(19) The acoustic barrier 40 further comprises two hook and loop (e.g. Velcro) closure portions 48, 50, one at each lateral end of the acoustic dampening layer 42. Both closure portions 48, 50 are disposed on the opposite side of the acoustic dampening layer 42 from the magnetic elements 46, so that in use with the acoustic barrier 40 wrapped around the pile 10, the closure portions 48, 50 are disposed on the radially outer surface of the acoustic dampening layer 42 whilst the magnetic elements 46 are disposed on the radially inner surface.

(20) A first closure portion 48 is attached to the acoustic dampening layer 42 at a first lateral end (the right end in FIG. 3) so as to extend laterally beyond the acoustic dampening layer 42. A second closure portion 50 is attached to the acoustic dampening layer 42 at a second opposing lateral end (the left end in FIG. 3) so that in use, as the acoustic barrier 40 is wrapped around the pile, the first closure portion 48 overlaps the second closure portion 50 to close the acoustic barrier 40 around the pile.

(21) Two example pile driving methods in which the noise is controlled using the acoustic barriers 30, 40 will now be described.

(22) According to a first example pile driving method shown in FIGS. 4 to 6, a pile 10 is partially inserted into a bore drilled into the ground 60 in preparation for driving the pile 10 into the ground 60. The acoustic barrier 30 for the hammer 20 is assembled onto the hammer 20 by installing the support frame 32 on the hammer 20 by bolts, and by attaching the acoustic dampening layer 38 to the support frame 32 by clips, as described above.

(23) The acoustic barrier 40 for the pile 10 is wrapped around an axial portion of the pile 10 elevated from ground level so that it is magnetically held on the pile 10 by the magnetic elements 46 of the arrays 44 (FIG. 4). The hook and loop closure portions 48, 50 are attached to each other to secure the lateral ends of the acoustic barrier 40 in place.

(24) The hammer 20 is then operated to drive an axial length of the pile 10 into the ground 60 in a pile driving operation. The acoustic barrier 40 remains held on the axial portion of the pile 10 and moves downwardly with the pile 10 towards the ground (FIG. 5).

(25) The acoustic barrier 40 is then repositioned to a relatively higher axial portion of the pile 10 before it reaches ground level. In this example method, a threshold of 1 m above ground level is set, and the pile driving operation is temporarily stopped when the acoustic barrier 40 is closer than 1 m to the ground so that it can be repositioned.

(26) In this example method, the acoustic barrier 40 is repositioned by removing it (unwrapping it) from the axial portion of the pile 10 to which it is attached, and re-wrapping it around a relatively higher portion of the pile 10.

(27) In other pile driving methods, a plurality of acoustic barriers 40 may be wrapped around the pile 10, and the lowermost acoustic barrier 40 may be removed and repositioned to an unoccupied space on the pile 01 when it reaches a threshold distance above ground level. Accordingly, a pile driver operator can make maximum use of the number of acoustic barriers available to them. For example, two acoustic barriers may be available and may initially be wrapped around axially separated portions of the pile 10. When one of the acoustic barriers approaches ground level it may be repositioned to a relatively higher axial portion of the pile 10, which may be above or below the other of the acoustic barriers.

(28) A second example method of pile driving is shown in FIGS. 7 and 8. This second example method differs from the first method in that the pile 10 is initially prepared by wrapping a plurality of acoustic barriers 40 around adjacent axial portions of the pile so that they are disposed substantially axially end-to-end on the pile 10. This method may provide for maximum acoustic dampening from the pile 10 as the protruding part of the pile is surrounded by acoustic dampening material. As before, the lowest acoustic barrier 40 is initially wrapped around an axial portion of the pile 10 that is elevated above ground level.

(29) The hammer 20 is then operated to drive an axial length of the pile 10 into the ground 60 in a pile driving operation. The acoustic barriers 40 remain held on the respective axial portions of the pile 10 and move downwardly with the pile 10 towards the ground (FIG. 5).

(30) The lowermost acoustic barrier 40 is then removed from the pile 10 before it reaches ground level. In this example method, a threshold of 1 m above ground level is set, and the pile driving operation is temporarily stopped when the acoustic barrier 40 is closer than 1 m to the ground so that it can be removed.

(31) In an alternative pile driving method, there may be a single acoustic barrier 40 that is wrapped around an upper axial portion of the pile (e.g. a portion adjacent the top of the pile 10), which may be removed as it approaches ground level or passes a threshold distance above ground level.

(32) In use, the acoustic barrier 30 attached to the hammer 20 dampens the noise from the drop weight of the hammer 20 and the impact on the pile, and the or each acoustic barrier 40 wrapped around the pile 10 dampens the noise from the pile 10. In particular, it is known that piles, such as hollow steel piles, may ring or reverberate during a pile driving operation. The or each acoustic barrier 40 acts to dampen the ringing or reverberating sound of the pile 10 during pile driving, thereby reducing the environmental impact of pile driving on the immediate surroundings.

(33) The acoustic barrier 30 for the hammer 20 and the acoustic barrier 40 for the pile 10 can be used to dampen noise substantially at the source of noise generation. Accordingly, the acoustic barriers of the invention may therefore be more effective in controlling noise from a pile driving operation than acoustic barriers installed around the perimeter of a construction site. Further, use of acoustic barriers according to the invention may mean that expensive acoustic barriers for the perimeter of a construction site may not be required in order to control noise from a pile driving operation.