Pile with sound abatement

Abstract

A noise-attenuating pile comprising a pile driving shoe, an outer tube that engages the pile driving shoe, and an inner member that extends through the outer tube and engages the pile driving shoe, wherein the pile is configured to be installed in sediment or other suitable material by driving the inner member with a pile driver, without directly impacting the outer tube, such that the radial outer tube is substantially insulated from the radial expansion waves generated by the pile driver impacting the inner member. In some piles, one of the inner member and the outer tube are removable after installation. In some piles, a seal is provided in a lower end of the channel defined between the inner member and the outer tube, which may be biodegradable, or may be an inflatable bladder, for example.

Claims

1. A pile configured for noise abatement during installation, the pile comprising: a pile driving shoe; an outer tube having a first end fixed to the pile driving shoe such that the outer tube remains engaged with the pile driving shoe when the pile is driven into place, the outer tube having a distal end extending away from the pile driving shoe; an inner member disposed in the outer tube such that a proximal end of the inner member engages the pile driving shoe, thereby defining an annular channel between the outer tube and the inner member, wherein a portion of the inner member extends distally away from the distal end of the outer tube when the proximal end of the inner member engages the pile driving shoe; and an elastomeric annular seal disposed near a lower end of the annular channel and configured to seal a lower end of the annular channel; wherein the pile is configured to be driven into place by a pile driver impacting the inner member without impacting the outer tube.

2. The pile of claim 1, wherein one of the inner member and the outer tube is configured to be removed after the pile is driven into place.

3. The pile of claim 1, wherein the annular seal is fixed to a lower portion of the inner member.

4. The pile of claim 1, wherein the annular seal comprises a biodegradable material.

5. The pile of claim 1, wherein the inflatable bladder further comprises an elongate fill tube that extends upwardly from the bladder to a top end of the annular channel.

6. The pile of claim 5, wherein the inflatable bladder is configured to be inflated with water.

7. The pile of claim 1, wherein the annular channel is substantially filled with a compressible material.

8. The pile of claim 7, wherein the compressible material comprises air or a polymeric foam.

9. The pile of claim 1, wherein the inner member comprises a metal tube.

10. The pile of claim 1, wherein 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.

11. The pile of claim 10, wherein the spring member comprises a plurality of stacked O-rings disposed between the first annular flange and the second annular flange.

12. The pile of claim 10, wherein the spring member comprises a compression spring.

13. The pile of claim 1, further comprising an elastic ring-shaped member disposed between the outer tube and the pile driving shoe.

14. The pile of claim 1, wherein the inner member engages the pile driving shoe through a spring.

15. The pile of claim 14, wherein the spring is disposed in a recess formed in the pile driving shoe.

16. The pile of claim 14, wherein the spring is integrally formed in the proximal end of the inner member.

17. The pile of claim 14, wherein the spring comprises a plurality of O-rings.

18. A method for driving a pile comprising 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; providing an elastomeric seal near a lower end of the annular channel that is configured to seal the lower end of the annular channel, wherein the elastomeric seal is fixed to the inner member; positioning the pile assembly at a desired location for installation; installing the pile assembly with a pile driver by driving the inner member such that the pile driving shoe pulls the outer tube into place; and removing one of the outer tube and the inner member.

19. The method of claim 18, wherein the inner member is configured to be removable.

20. The method of claim 18, wherein the seal comprises an inflatable bladder.

21. The method of claim 18, wherein the inner member engages the pile driving shoe through an elastic spring.

22. A pile configured for noise abatement during installation, the pile comprising: a pile driving shoe; an outer tube having a first end fixed to the pile driving shoe such that the outer tube remains engaged with the pile driving shoe when the pile is driven into place, the outer tube having a distal end extending away from the pile driving shoe; an inner member disposed in the outer tube such that a proximal end of the inner member engages the pile driving shoe, thereby defining an annular channel between the outer tube and the inner member, wherein a portion of the inner member extends distally away from the distal end of the outer tube when the proximal end of the inner member engages the pile driving shoe; and an elastomeric annular seal disposed near a lower end of the annular channel and configured to seal a lower end of the annular channel; wherein the pile is configured to be driven into place by a pile driver impacting the inner member without impacting the outer tube; wherein 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.

23. A pile configured for noise abatement during installation, the pile comprising: a pile driving shoe; an outer tube having a first end fixed to the pile driving shoe such that the outer tube remains engaged with the pile driving shoe when the pile is driven into place, the outer tube having a distal end extending away from the pile driving shoe; an inner member disposed in the outer tube such that a proximal end of the inner member engages the pile driving shoe, thereby defining an annular channel between the outer tube and the inner member, wherein a portion of the inner member extends distally away from the distal end of the outer tube when the proximal end of the inner member engages the pile driving shoe; and an elastomeric annular seal disposed near a lower end of the annular channel and configured to seal a lower end of the annular channel; wherein the pile is configured to be driven into place by a pile driver impacting the inner member without impacting the outer tube, and the inner member engages the pile driving shoe through a spring.

24. A method for driving a pile comprising 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, wherein the inner member engages the pile driving shoe through an elastic spring; providing an elastomeric seal near a lower end of the annular channel that is configured to seal the lower end of the annular channel; positioning the pile assembly at a desired location for installation; installing the pile assembly with a pile driver by driving the inner member such that the pile driving shoe pulls the outer tube into place; and removing one of the outer tube and the inner member.

Description

DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIGS. 1A-1D illustrate the primary wave fronts associated with the Mach cone generated by a representative pile compression wave;

(3) FIG. 2 illustrates only the first upwardly traveling wave front for the representative pile compression wave illustrated in FIGS. 1A-1D;

(4) FIG. 3 illustrates two piles in accordance with the present invention, wherein one pile (on the left) is in position to be driven into an installed position, and the other pile (on the right) is shown installed and in cross section;

(5) FIG. 4 shows another embodiment of a pile in accordance with the present invention;

(6) FIG. 5 shows a fragmentary view of the distal end of an embodiment of a pile in accordance with the present invention;

(7) FIG. 6 illustrate an elastic connection mechanisms that may alternatively be used to isolate the outer tube from the inner member in alternative embodiments of a pile in accordance with the present invention; and

(8) FIGS. 7A-7C illustrate a pile in accordance with the present invention, wherein the inner member is removed after installing the pile;

(9) FIGS. 8A-8E illustrate a method for installing a pile with a removable outer tube, such that only the inner member remains in place after installation;

(10) FIG. 9 is a cross-sectional view of another pile in accordance with the present invention with an elastic connection between the inner member and the driving shoe, and with an inflatable seal; and

(11) FIGS. 10A and 10B illustrate another pile in accordance with the present invention with a spring and/or seal connecting the inner member and the outer tube above the driving shoe.

DETAILED DESCRIPTION

(12) 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.

(13) 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*10.sup.8exp(t/0.004)Pa(1)

(14) The acoustic medium was modeled as a fluid using measured water sound speed at the test site, c.sub.w, and estimated sediment sound speed, c.sub.s, 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.

(15) 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.

(16) Pressure time series recorded by two hydrophones located about 8 m from the pile showed the following key features:

(17) 1. The first and highest amplitude arrival is a negative pressure wave of the order of 10-100 kPa;

(18) 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

(19) 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.

(20) 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.

(21) The primary source of underwater sound originating from pile driving is associated with compression of the pile. Refer to FIGS. 1A-1D, which illustrate schematically the transient behavior of the reactions associated with an impact of a pile driver (not shown) with a pile 90. In FIG. 1A, the compression wave in the pile due to the hammer strike produces an associated radial displacement motion due to the effect of Poisson's ratio of steel (0.33). This radial displacement in the pile propagates downwards (indicated by downward arrow) with the longitudinal wave with wave speed of c.sub.p=4,840 m/s when the pile 90 is surrounded by water 94. Since the wave speed of this radial displacement wave is higher than the speed of sound in the water 94 the rapidly downward propagating wave produces an acoustic field in the water 94 in the shape of an axisymmetric cone with an apex traveling along with the pile deformation wave front. This Mach cone is formed with a cone angle of .sub.w=sin.sup.1(c.sub.w/c.sub.p)=17.9.

(22) 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 FIG. 1B, the Mach cone angle changes from .sub.w to .sub.s=sin.sup.1(c.sub.w/c.sub.p)=19.7 as the pile bulge wave enters sediment 92. Note that the pile bulge wave speed in the sediment 92 is slightly lower due to the higher mass loading of the sediment 92 and is equal to c.sub.p=4,815 m/s.

(23) As the wave in the pile reaches the pile 90 terminal end it is reflected upwards (FIG. 1C). This upward traveling wave in turn produces a Mach cone of angle .sub.s (defined as negative with respect to horizontal) that is traveling up instead of down. The sound field associated with this cone propagates up through the sediment 92 and penetrates into the water 94. Due to the change in the speed of sound going from sediment 92 to water 94 the angle of the wave front that originates in the sediment 92 changes from .sub.s to .sub.sw=30.6 following Snell's law. Ultimately, two upward moving wave fronts occur as shown schematically in FIG. 1D and more clearly in FIG. 2. One wave front is oriented with angle .sub.sw and the other wave front with angle .sub.ws. The latter is produced directly by the upward moving pile wave front in the water 94. (Other features of propagation such as diffraction and multiple reflections are not depicted in these schematic illustrations, for clarity.)

(24) 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.

(25) 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 FIG. 2, an upwardly traveling wave front propagates through the sediment 92 with a sound speed c.sub.w. This wave front may enter the water outside of the enclosure defined by any temporary barrier, such as a bubble curtain or TNAP system, for example, such that the temporary barrier will have little effect on this component of the sound.

(26) FIG. 3 illustrates a pair of noise-attenuating piles 100 in accordance with the present invention. In FIG. 3, the noise-attenuating pile 100 on the left is shown in position to be driven into the desired position with a pile driver 98, which is schematically indicated in phantom at the top of the pile 100. The identical noise-attenuating pile 100 on the right in FIG. 3 is shown in cross section, and installed in the sediment 92.

(27) 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.

(28) 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 -inch wall thickness, and the annular channel 103 is about six inches thick.

(29) 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.

(30) 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.

(31) It will be appreciated from FIG. 3 that the inner tube 104 is longer than the outer tube 102, such that a portion 112 of the inner tube 104 extends upwardly beyond the outer tube 102. This configuration facilitates the pile driver 98 engaging and impacting only the inner tube 104. It is contemplated that other means may be used to enable the driver to impact the inner tube 104 without impacting the outer tube 102. For example, the pile driver 98 may be formed with an engagement end or an adaptor that fits within the outer tube 102. The important aspect is that the pile 100 is configured such that the pile driver 98 does not impact the outer tube 102, but rather impacts only the inner tube 104.

(32) 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.

(33) 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.

(34) A second embodiment of a noise-attenuating pile 200 in accordance with the present invention is shown in cross-sectional view in FIG. 4. In this embodiment the pile 200 includes an outer tube 202, which may be substantially the same as the outer tube 102 discussed above. A solid inner member 204 extends generally concentrically with the outer tube 202, and is formed from concrete. The inner member 204 may have a hexagonal horizontal cross section, for example. A tapered driving shoe 206 is disposed at the distal end of the pile 200, and is conical or frustoconical in shape, and may include a recess 207 that receives the inner member 204. In a currently preferred embodiment the driving shoe 206 is made of steel. The outer tube 202 is attached to the driving shoe 206, for example, by welding or the like. The inner member 204 in this embodiment extends above the proximal end of the outer tube 204. Although not a part of the pile 200, a wooden panel 205 is illustrated at the top of the inner member 204, which spreads the impact loads from the pile driver, to protect the concrete inner member 204 from crumbling during the driving process. Optionally, in this embodiment a filler 216 such as a polymeric foam substantially fills the annular volume between the outer tube 202 and the inner member 204.

(35) 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.

(36) FIG. 5 shows a fragmentary cross-sectional view of an alternative embodiment of a pile 250 having an inner tube 254 and an outer tube 252. The pile 250 is similar to the pile 100 disclosed above, but wherein the driver shoe 256 is formed integrally with the inner tube 254. In this embodiment, the distal end portion of the inner tube 254 includes an outer projection or flange 260. For example, the flange 260 may be formed separately and welded or otherwise affixed to the distal end portion of the inner tube 254. The outer tube 252 is configured with a corresponding annular recess 253 on an inner surface, which is sized and positioned to retain or engage the flange 260. In an exemplary construction method the outer tube 252 is formed from two pieces, an elongate upper piece 251 having an inner circumferential groove on its bottom end, and a distal piece 259 having a corresponding inner circumferential groove on its upper end. The distal piece 259 may further be formed in two segments to facilitate placement about the inner tube 254. The upper piece 251 and distal piece 259 may then be positioned about the inner tube 254 such that the flange 260 is captured in the annular recess 253, and the upper piece 251 and distal piece 259 welded 257 or otherwise fixed together. The inner tube 254 and outer tube 252 are therefore interlocked by the engagement of the inner tube flange 260 and the outer tube annular recess 253. One or two low-friction members 258 (two shown), for example nylon washers, may optionally be provided.

(37) In the embodiment of FIG. 5, the flange 260 is sized such that a gap is formed between an outer surface of the flange 260 and an inner surface of the annular recess 253. Also, the length of the outer tube 252 is configured to provide a gap 262 between the bottom of the outer tube 253, and the horizontal surface of the shoe 256 near the distal end of the inner tube 254. It will now be appreciated that as the radial displacement waves induced by the pile driver travel along the inner tube 254 the outer tube 252 will be further isolated from the radial displacement waves due to these gap 262. An annular channel between the inner tube 254 and the outer tube 252 in this embodiment may optionally be sealed with a sleeve, which may be formed with a polymeric foam or other sealing material as are known in the art.

(38) Although a flange and recess connection is shown in FIG. 5, it is also contemplated, as illustrated in FIG. 6, that a pile 280 in accordance with the present invention may include an elastic or compliant connector 285 may alternatively be provided between the inner tube 284 and the outer tube 282 of the pile 280. It is contemplated, for example, that the elastic connector 285 connecting the inner tube and outer tube may be an annular linear elastic spring member with an inner edge fixed to the inner tube 284, and an outer edge fixed to the outer tube 282. In this embodiment the driving shoe 286 is formed integrally with the inner and outer tubes 284, 282, and the elastic connector 285 substantially isolates the outer tube 282 from the radial compression waves induced in the inner tube 284 by the driver.

(39) 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.

(40) Another noise-attenuating pile 300 in accordance with the present invention is shown in cross-sectional view in FIGS. 7A-7C. The pile 300 includes an outer tube 302 that is fixed to a driving shoe 306. For example, the outer tube 302 and driving shoe 306 may be substantially the same as the corresponding components described above.

(41) 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 FIG. 7B the inner member 304 extends above the upper end of the outer tube 302 when the inner member 304 engages the driving shoe 306. Alternatively, a rigid adapter or insert may be provide that extends into the upper end of the outer tube 302 to engage the inner member 304 and transmit the hammer impulses thereto during installation.

(42) 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.

(43) Optionally an upper seal 316 spacer may be provided near an upper end of the annular channel 303.

(44) 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.

(45) FIG. 7A shows the inner member 304 with the first seal being inserted into the outer tube 302, as indicated by arrow 80. In some applications the inner member 304 may be inserted before the pile is placed in the water. The assembled pile 300 may then be positioned at a desired location on the sediment 92 for installation. Alternatively, the shoe 306 and outer tube 302 assembly may be pre-positioned, and the inner member 304 inserted in situ. Suction or pump means (not shown) may then be used to remove water from the annular channel 303 prior to driving the pile 300.

(46) FIG. 7B shows the pile 300 after it has been driven into the sediment 92. The inner member 304 may then be removed, as indicated by the arrow 81. It is contemplated that the lower seal 315 may be formed from a degradable material, for example from a suitable biopolymer, to facilitate removal of the inner member 304 after installation.

(47) FIG. 7C illustrates the installed pile 300 after removal of the inner member 304.

(48) 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.

(49) A sequence for installation of a pile 350 with a removable outer tube 352 is shown in FIGS. 8A-8E. In FIG. 8A the pile 350 is shown positioned with the driving shoe 356 on the ground or sediment 92 and ready for installation with a pile driver (not shown). The inner member 354 extends upwardly from the driving shoe 356 beyond the top of the outer tube 352, and is readily driven without impacting the outer tube 352. In FIG. 8B the pile 350 is shown driven into the sediment 92. Both the outer tube 352 and the inner member 354 remain directly engaged with the driving shoe 356. Optionally, the outer tube 352 may be decoupled from the shoe 356, and the inner member 354 driven further into the sediment 92. However, as discussed above this may not be desired because it may result in pressure waves being transmitted from the inner member 354, through the sediment 92, and into the water 94. The outer tube 354 may then be pulled out of the sediment 92, which is facilitated if the driving shoe 356 has a larger maximum radius that the outer tube 352. The outer tube 352 may be slightly tapered, for example by 1-3 degrees to facilitate removal. Removal of the outer tube 352 may be aided by rotating and/or vibrating the outer tube 352 about its axis. It is also contemplated that a bubble generator (not shown) may be provided on or in the perimeter of driving shoe 356, and connected with a pressurized gas source, to facilitate removal of the outer tube 354.

(50) Another pile 400 in accordance with the present invention is shown in FIG. 9. The pile 400 is similar to the pile 300 described above, and similar aspects will not be repeated here, for brevity and clarity. In this embodiment the outer tube 402 and inner member 404 define an annular channel 403 therebetween, and the outer tube 402 is fixedly attached to the driving shoe. To further isolate the outer tube 402 from reflected radial compression waves during installation, the inner member 404 engages the driving shoe through an elastic member 409. In this embodiment an annular recess 410 is provided in the driving shoe that receives the elastic member 409, and the lower end 405 of the inner member 404 is sized and shaped to be inserted into the recess 410. Optionally, the lower end 405 may be narrower than the upper portion of the inner member 404, such that a ledge or abutment 407 is defined to provide a positive stop limiting the longitudinal travel of the inner member 404. Therefore, when the inner member 404 is hammered to install the pile 400, the peak impulse transmitted from the inner member 404 to the driving shoe is reduced, thereby reducing the radial compression wave generated in the outer tube 402.

(51) 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.

(52) 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 FIG. 9 may be reversed with the elastic member 409 inserted into a recess in the inner member 404, and an annular extension provided on the driving shoe. Alternatively, the bottom portion of the inner member 404 may be configured to increase its elasticity or spring-like properties. For example, the bottom of the inner member 404 may be constructed from a more elastic material or modified to increase its elasticity, e.g., by providing apertures or recesses in the lower end of the inner member 404, or reducing the thickness thereof.

(53) FIG. 9 also shows an annular bladder-type seal 415 fixed to the inner member 404. The bladder-type seal 415 includes one or more fill tubes 417 that extend upwardly along the annular channel 403, with a valve 419 at a distal end, for filling the bladder-type seal 415. The inner member 404 in this embodiment is inserted into the outer tube 402 with the bladder-type seal 415 deflated, to facilitate placement. The valve 419 is connected to a high-pressure fluid source or pump (not shown), and the seal 415 is inflated to a design pressure to form the desired seal. The fluid for the seal may be, for example, a fluid such as water or hydraulic oil, or a gas, such as air. An optional upper seal 416 is also shown.

(54) A portion of another pile 500 is shown in FIGS. 10A and 10B, wherein FIG. 10A shows an exploded view of the lower end of the pile 500, and FIG. 10B shows the assembled pile 500. The driving shoe 506 is attached to the inner member 504 with a plurality of bolts 507 that extend through the shoe 506 and engage the threaded apertures 513 in the bottom of the inner member 504.

(55) 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.

(56) 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.

(57) 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.