Patent Grant
9617702
Pile driving in water produces extremely high sound levels in the surrounding environment in air and underwater. For example, underwater sound levels as high as 220 dB re 1 μPa are not uncommon ten meters away from a steel pile as it is driven into the sediment with an impact hammer.
Reported impacts on wildlife around a construction site include fish mortality associated with barotrauma, hearing impacts in both fish and marine mammals, and bird habitat disturbance. Pile driving in water is therefore a highly regulated construction process and can only be undertaken at certain time periods during the year. The regulations are now strict enough that they can severely delay or prevent major construction projects.
There is thus significant interest in reducing underwater noise from pile driving either by attenuating the radiated noise or by decreasing noise radiation from the pile. As a first step in this process it is necessary to understand the dynamics of the pile and the coupling with the water as the pile is driven into sediment. The process is a highly transient one in that every strike of the pile driving hammer on the pile causes the propagation of deformation waves down the pile. To gain an understanding of the sound generating mechanism the present inventors have conducted a detailed transient wave propagation analysis of a submerged pile using finite element techniques. The conclusions drawn from the simulation are largely verified by a comparison with measured data obtained during a full scale pile driving test carried out by the University of Washington, the Washington State Dept. of Transportation, and Washington State Ferries at the Vashon Island ferry terminal in November 2009.
Prior art efforts to mitigate the propagation of dangerous sound pressure levels in water from pile driving have included the installation of sound abatement structures in the water surrounding the piles. For example, in Underwater Sound Levels Associated With Pile Driving During the Anacortes Ferry Terminal Dolphin Replacement Project, Tim Sexton, Underwater Noise Technical Report, Apr. 9, 2007 (“Sexton”), a test of sound abatement using bubble curtains to surround the pile during installation is discussed. A bubble curtain is a system that produced bubbles in a deliberate arrangement in water. For example, a hoop-shaped perforated tube may be provided on the sediment surrounding the pile, and provided with a pressurized air source, to release air bubbles near or at the sediment surface to produce a rising sheet of bubbles that act as a barrier in the water. Although significant sound level reductions were achieved, the pile driving operation still produced high sound levels.
Another method for mitigating noise levels from pile driving is described in a master's thesis by D. Zhou titled Investigation of the Performance of a Method to Reduce Pile Driving Generated Underwater Noise (University of Washington, 2009). Zhou describes and models a noise mitigation apparatus dubbed Temporary Noise Attenuation Pile (TNAP) wherein a steel pipe is placed about a pile before driving the pile into place. The TNAP is hollow-walled and extends from the sediment to above the water surface. In a particular apparatus disclosed in Zhou the TNAP pipe is placed about a pile having a 36-inch outside diameter. The TNAP pipe has an inner wall with a 48-inch O.D., and an outer wall with a 54-inch O.D. A 2-inch annular air gap separates the inner wall from the outer wall.
Although the TNAP did reduce the sound levels transmitted through the water, not all criteria for noise reduction were achieved.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In an embodiment, a noise-abating pile includes a pile driving shoe, and an outer tube fixed to the pile driving shoe, and extending away from the shoe. An inner member is disposed in the outer tube and engages the driving shoe, such that an annular channel is defined therebetween. The inner member is longer than the outer tube and extends away from the distal end of the outer tube. An annular seal id provided near a lower end of the annular channel. The pile is configured to be driven by a pile driver impacting the inner member without impacting the outer tube.
In an embodiment, the one of the inner member and the outer tube is configured to be removed after the pile is driven into the place.
In an embodiment, the annular seal is fixed to a lower portion of the inner member.
In an embodiment, the annular seal comprises a biodegradable material.
In an embodiment, the annular seal comprises an inflatable bladder, for example, the inflatable bladder may include one or more elongate fill tubes that extends upwardly from the bladder to a top end of the annular channel. For example, the inflatable bladder is configured to be inflated with water.
In an embodiment, the annular channel is substantially filled with a compressible material, for example, air or a polymer foam.
In an embodiment, the inner member comprises a metal tube.
In an embodiment, the outer tube further comprises a first annular flange extending inwardly from a lower portion of the outer tube, and the inner member further comprises a second annular flange extending outwardly from a lower portion of the inner member, and further comprising an elastic spring member disposed between the first annular flange and the second annular flange. For example, the spring member may be formed as a plurality of stacked O-rings disposed between the first annular flange and the second annular flange, as a compression spring, or the like.
In an embodiment, a relatively elastic ring-shaped member is disposed between the outer tube and the pile driving shoe.
In an embodiment, the inner member engages the pile driving shoe through a spring. For example, the spring may be disposed in a recess formed in the pile driving shoe, may be integrally formed in the proximal end of the inner member, or may be formed as a plurality of O-rings.
A method for driving a pile into a substrate, for example sediment, includes the steps of assembling a pile driving shoe, an outer tube, and an inner member to define a pile assembly having an annular channel defined between the outer tube and the inner member, wherein at least one of the outer tube and the inner member are configured to be removable from the pile driving shoe after the pile assembly is installed; positioning the pile assembly at a desired location for installation; installing the pile assembly with a pile driver; and removing one of the outer tube and the inner member.
In an embodiment, the inner member is configured to be removable.
In an embodiment, the inner member further comprises a seal that sealingly engages a lower end of the annular channel.
In an embodiment, the seal comprises an inflatable bladder.
In an embodiment, the inner member engages the pile driving shoe through an elastic spring.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
To investigate the acoustic radiation due to a pile strike we created an axisymmetric finite element model of a 30-inch radius, 32 m long hollow steel pile with a wall thickness of one inch submerged in 12.5 m of water and driven 14 m into the sediment. The radius of the water and sediment domain was 10 m. Perfectly matched boundary conditions were used to prevent reflections from the boundaries that truncate the water and sediment domains. The pile was fluid loaded via interaction between the water/sediment. All domains were meshed using quadratic Lagrange elements.
The pile was impacted with a pile hammer with a mass of 6,200 kg that was raised to a height of 2.9 m above the top of the pile. The velocity at impact was 7.5 m/s, and the impact pressure as a function of time after impact was examined using finite element analysis and approximated as:
P(t)=2.7*108exp(−t/0.004)Pa (1)
The acoustic medium was modeled as a fluid using measured water sound speed at the test site, cw, and estimated sediment sound speed, cs, of 1485 m/s and 1625 m/s, respectfully. The sediment speed was estimated using coring data metrics obtained at the site, which is characterized by fine sand, and applied to empirical equations.
The present inventors conducted experiments to measure underwater noise from pile driving at the Washington State Ferries terminal at Vashon Island, Wash., during a regular construction project. The piles were approximately 32 m long and were set in 10.5 to 12.5 m of water depending on tidal range. The underwater sound was monitored using a vertical line array consisting of nine hydrophones with vertical spacing of 0.7 m, and the lowest hydrophone placed 2 m from the bottom. The array was set such that the distance from the piles ranged from 8 to 12 m.
Pressure time series recorded by two hydrophones located about 8 m from the pile showed the following key features:
1. The first and highest amplitude arrival is a negative pressure wave of the order of 10-100 kPa;
2. The main pulse duration is ˜20 ms over which there are fluctuations of 10 dB; during the next 40 ms the level is reduced by 20 dB; and
3. There are clearly observable time lags between measurements made at different heights off the bottom. These time lags can be associated with the vertical arrival angle.
The finite element analysis shows that the generation of underwater noise during pile driving is due to a radial expansion wave that propagates along the pile after impact. This structural wave produces a Mach cone in the water and the sediment. An upward moving Mach cone produced in the sediment after the first reflection of the structural wave results in a wave front that is transmitted into the water. The repeated reflections of the structural wave cause upward and downward moving Mach cones in the water. The corresponding acoustic field consists of wave fronts with alternating positive and negative angles. Good agreement was obtained between a finite element wave propagation model and measurements taken during full scale pile driving in terms of angle of arrival. Furthermore, this angle appears insensitive to range for the 8 to 12 m ranges measured, which is consistent with the wave front being akin to a plane wave.
The primary source of underwater sound originating from pile driving is associated with compression of the pile. Refer to
Note that this is the angle formed between the vertically oriented pile 90 and the wave front associated with the Mach cone; it is measured with a vertical line array, and here it will be manifested as a vertical arrival angle with reference to horizontal. This angle only depends on the two wave speeds and is independent of the distance from the pile. As illustrated in
As the wave in the pile reaches the pile 90 terminal end it is reflected upwards (
Based on finite element analyses performed to model the transient wave behavior generated from impacts generated when driving a steel pile, the generation of underwater noise during pile driving is believed to be due to a radial expansion wave that propagates along the pile after impact. This structural wave produces a Mach cone in the water and the sediment. An upwardly moving Mach cone produced in the sediment after the first reflection of the structural wave results in a wave front that is transmitted into the water. Repeated reflections of the structural wave cause upward and downward moving Mach cones in the water.
It is believed that prior art noise attenuation devices, such as bubble curtains and the TNAP discussed above, have limited effectiveness in attenuating sound levels transmitted into the water because these prior art devices do not address sound transmission through the sediment. As illustrated most clearly in
The noise-attenuating pile 100 includes a structural outer tube 102, a generally concentric inner tube 104, and a tapered driving shoe 106. In a current embodiment the outer tube 102 is sized and configured to accommodate the particular structural application for the pile 100, e.g., to correspond to a conventional pile. In one exemplary embodiment the outer tube 102 is a steel pipe approximately 89 feet long and having an outside diameter of 36 inches and a one-inch thick wall. Of course, other dimensions and/or materials may be used and are contemplated by the present invention. The optimal size, material, and shape of the outer tube 102 will depend on the particular application. For example, hollow concrete piles are known in the art, and piles having non-circular cross-sectional shapes are known. As discussed in more detail below, the outer tube 102 is not impacted directly by the pile driver 98, and is pulled into the sediment 92 rather than being driven directly into the sediment. This aspect of the noise-attenuating pile 100 will facilitate the use of non-steel structural materials for the outer tube 102, such as reinforced concrete.
The inner tube 104 is generally concentric with the outer tube 102 and is sized to provide an annular channel or space 103 between the outer tube 102 and the inner tube 104. The inner tube 104 may be formed from a material similar to the inner tube 104, for example, steel, or may be made of another material such as concrete. For example, the inner tube 104 may be concrete. It is also contemplated that the inner tube 104 may be formed as a solid elongate rod rather than tubular. In a particular embodiment, the inner tube 104 comprises a steel pipe having an outside diameter of 24 inches and a ⅜-inch wall thickness, and the annular channel 103 is about six inches thick.
In a particular embodiment the outer tube 102 and the inner tube 104 are both formed of steel. The outer tube 102 is the primary structural element for the pile 100, and therefore the outer tube 102 is thicker than the inner tube 104. The inner tube 104 is structurally designed to transmit the impact loads from the pile driver 98 to the driving shoe 106.
The driving shoe 106 in this embodiment is a tapered annular member having a center aperture 114. The driving shoe 106 has a wedge-shaped cross section, tapering to a distal end defining a circular edge, to facilitate driving the pile 100 into the sediment 92. In a current embodiment the driving shoe 106 is steel. The outer tube 102 and inner tube 104 are fixed to the proximal end of the driving shoe 106, for example, by welding 118 or the like. Other attachment mechanisms may alternatively be used; for example, the driving shoe 106 may be provided with a tubular post portion that extends into the inner tube 104 to provide a friction fit. The driving shoe 106 maximum outside diameter is approximately equal to the outside diameter of the outer tube 102, and the center aperture 114 is preferably slightly smaller than the diameter of an axial channel 110 defined by the inner tube 104. It will be appreciated that the center aperture 114 permits sediment to enter into the inner tube 104 when the pile 100 is driven into the sediment 92. The slightly smaller diameter of the driving shoe center aperture 114 will facilitate sediment entering the inner tube 104 by reducing wall friction effects within the inner tube 104.
It will be appreciated from
At or near the upper end of the pile 100, a compliant member 116, for example an epoxy or elastomeric annular sleeve, may optionally be provided in the annular channel 103 between the inner tube 104 and the outer tube 102. The compliant member 116 helps to maintain alignment between the tubes 102, 104, and may also provide an upper seal to the annular channel 103. Although it is currently contemplated that the annular channel 103 will be substantially air-filled, it is contemplated that a filler material may be provided in the annular channel 103, for example, a spray-in foam or the like. The filler material may be desirable to prevent significant water from accumulating in the annular channel 103, and/or may facilitate dampening the compression waves that travel through the inner tube 104 during installation of the pile 100.
The advantages of the construction of the pile 100 can now be appreciated with reference to the preceding analysis. As the inner tube 104 is impacted by the pile driver 98, a deformation wave propagates down the length of the inner tube 104, and is reflected when it reaches the driving shoe 106, to propagate back up the inner tube 104, as discussed above. The outer tube 102 portion of the pile 100 substantially isolates both the surrounding water 94 and the surrounding sediment 92 from the traveling Mach wave, thereby mitigating sound propagation into the environment. The outer tube 102, which in this embodiment is the primary structural member for the pile 100, is therefore pulled into the sediment by the driving shoe 106, rather than being driven into the sediment through driving hammer impacts on its upper end.
A second embodiment of a noise-attenuating pile 200 in accordance with the present invention is shown in cross-sectional view in
It is contemplated that in an alternate similar embodiment, an outer tube may be formed of concrete, and an inner tube or solid member may be formed from steel or a similarly suitable material.
In the embodiment of
Although a flange and recess connection is shown in
Although the piles 100, 200 are shown in a vertical orientation, it will be apparent to persons of skill in the art, and is contemplated by the present invention, that the piles 100, 200 may alternatively be driven into sediment at an angle.
Another noise-attenuating pile 300 in accordance with the present invention is shown in cross-sectional view in
A removable inner member 304 is sized and configured to be inserted into the outer tube 302, and positioned to define an annular channel 303 therebetween. The annular channel may be, for example, greater than one inch thick. The removable inner member 302 is sized to abut or engage the driving shoe 306 when fully inserted into the outer tube 302. As discussed with reference to the piles 100, 200 disclosed above, the pile 300 is configured such that only the inner member 304 is impacted during installation of the pile 300. For example, as seen most clearly in
A first seal 315 is fixed to the inner member 304, and engages an inner wall of the outer tube 302. The first seal 315 is configured to seal the annular channel 303 near a lower end of the inner member 304 to prevent or limit the incursion of water into the channel 303 during installation. Although a single ring-shaped seal 315 is shown on the inner member 304, it will be apparent to persons of skill in the art that other seal arrangements may be used. For example, one or more O-ring seals may be used, or the seal may be fixed to an inner wall of the outer tube 302 and sized to receive the inner member 304. In another alternative includes a combination of one or more seals fixed to the outer surface of the inner member 304 and one or more seals fixed to the inner surface of the outer tube 302. The annular channel is preferably filled with a compressible material, for example a gas such as air, a compressible foam, or the like.
Optionally an upper seal 316 spacer may be provided near an upper end of the annular channel 303.
It will be appreciated that the pile 300, similar to the piles 100, 200 disclosed above, the outer tube 302, which contacts the water and sediment directly, does not experience the high-energy radial expansion waves during installation.
It is also contemplated that with minor modifications that would be apparent to persons of skill in the art, the pile 300 may be configured with the inner member 304 fixed to the shoe 306, and the outer tube 302 configured to removably abut or otherwise engage the driving shoe 306.
A sequence for installation of a pile 350 with a removable outer tube 352 is shown in
Another pile 400 in accordance with the present invention is shown in
The elastic member 409 may be, for example, a stiff spring, a plurality of elastomeric washers, an annular block of elastomeric material, or a metal washer having a high Young's modulus.
It will be apparent to persons of skill in the art from the teachings herein that various alternative embodiments are possible. For example, the particular spring arrangement shown in
A portion of another pile 500 is shown in
An annular first flange member 510 extends inwardly from the outer tube 502. The first flange member 510 is shown fixed to the bottom edge of the outer tube 502, for example by welding or the like. However, any conventional means for attaching or forming the first flange 510 may be used. For example, the first flange may be formed with an L-shaped cross section, and the vertical leg bolted, welded, or otherwise fixed to an inner surface of the outer tube 502. A second annular flange member 508 extends outwardly from the inner member 504, and is positioned generally above the first flange member 510.
An elastic member or spring 509 is disposed between the first and second flange members 510, 508. For example, the spring 509 may be a stiff compression spring as are known in the art, or may comprise a length of tubular elastomeric material. In a particular embodiment the spring 509 is formed from a plurality of stacked elastomeric O-rings, that are configured to also provide a good seal to the annular channel 503 between the outer tube 502 and the inner member 504. Optionally, a ring-shaped member 511 formed from a relatively elastic material may also be provided between the driving shoe 506 and the outer tube 502, to further isolate the outer tube 502 from pressure waves reflected from the driving shoe 506. In this pile 500, the pile driver (not shown) impacts only the inner member 504, as discussed for other piles above, and a portion of the driving force is transmitted to the outer tube 502 through the second flange member 508, the spring 509, and the first flange member 510.
While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
This application claims the benefit of Provisional Application No. 61/876,101, filed Sep. 10, 2013. This application is also a continuation-in-part of application Ser. No. 13/574,231, filed Jul. 19, 2012, which is a U.S. National Stage of PCT/US2011/021723, filed Jan. 19, 2011, which claims the benefit of Provisional Application No. 61/296,413, filed Jan. 19, 2010. The entire disclosures of said applications are hereby incorporated by reference herein.
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