Patent application title: BUOYANCY STABILIZED PIER STRUCTURE AND METHOD FOR INSTALLING SAME
Roger Patten (Burien, WA, US)
IPC8 Class: AE01D1902FI
Class name: Bridges pier
Publication date: 2010-09-30
Patent application number: 20100242191
Patent application title: BUOYANCY STABILIZED PIER STRUCTURE AND METHOD FOR INSTALLING SAME
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
Origin: SEATTLE, WA US
IPC8 Class: AE01D1902FI
Publication date: 09/30/2010
Patent application number: 20100242191
A bridge pier structure is disclosed having a downwardly open footing
chamber, an upper buoyant chamber, an upright member that mechanically
connects these chambers, and that defines a fluid channel to the footing
chamber. A valve is disposed in an upper portion of the fluid channel and
configured to attach to a water ejection pump and a vacuum source. The
pressure in the footing chamber can be reduced, such that hydrostatic
pressure and the atmospheric pressure aids in embedding the footing.
Optionally, a vibrating apparatus attaches to the structure to facilitate
embedding. The apparatus may also enable the structure to be dislodged
after installation, by providing a high pressure air source to the valve.
The structure may be installed by towing it to location, positioning it
on the waterway bed, and applying a suction to the valve.
1. A bridge pier comprising:a footing chamber that is open downwardly;an
upper chamber defining a buoyant volume;an upright portion mechanically
connecting the footing chamber and the upper chamber, the upright portion
further comprising a fluid channel that extends from an upper end of the
upright portion to the footing chamber;a valve having an open position
and a closed position, the valve disposed in an upper portion of the
fluid channel and configured to attach to a vacuum source.
2. The bridge pier of claim 1, further comprising a vibratory device attached to the bridge pier and configured to selectively vibrate the bridge pier.
3. The bridge pier of claim 2, wherein the upper chamber comprises a plurality of separated volumes that are configured to selectively receive water to act as ballast tanks to facilitate installation of the bridge pier.
4. The bridge pier of claim 1, wherein the upper chamber is filled with a polymeric foam.
5. The bridge pier of claim 1, wherein the downwardly open footing chamber further comprises a chamfered lower edge.
6. The bridge pier of claim 1, wherein the bridge pier has a nominal design load, and wherein the upper chamber is sized and configured such that during use the upper chamber produces a buoyancy force that is equal to at least eighty percent of the nominal design load.
7. The bridge pier of claim 1, wherein the upright portion comprises a plurality of interconnected upright members.
8. The bridge pier of claim 7, wherein the plurality of upright members are telescopically interconnected.
9. The bridge pier of claim 1, wherein the footing chamber, the upper chamber, and the upright portion comprise a unitary structure.
10. The bridge pier of claim 1, wherein the bridge pier further comprises a bridge tower structure.
11. A method for installing a bridge pier comprising:fabricating a bridge pier having a buoyant upper chamber, a downwardly open footing chamber, and an upright portion defining a channel to the footing chamber;transporting the bridge pier to an installation location;sinking at least a portion of the bridge pier to position the footing chamber positioned on a waterbed;applying a vacuum to the channel such that a pressure in the footing chamber is reduced sufficiently to cause the footing chamber to become embedded in the waterbed.
12. The method of claim 11, wherein the bridge pier is fabricated at a location remote from the installation location.
13. The method of claim 11, wherein the step of transporting the bridge pier comprises towing the bridge pier in a waterway.
14. The method of claim 13, wherein the bridge pier is towed in a non-vertical orientation, and further comprising the step of reorienting the bridge pier to a vertical orientation prior to the step of sinking at least a portion of the bridge pier.
15. The method of claim 11, further comprising the step of vibrating the bridge pier to facilitate embedding the footing chamber in the waterbed.
16. The method of claim 11, wherein the upright portion of the bridge pier comprises at least two telescoping upright members.
17. The method of claim 16, wherein prior to the step of transporting the bridge pier the footing chamber is moved towards the upper chamber by telescoping the two upright members.
18. The method of claim 11, further comprising the step of injecting pressurized air into the footing chamber prior to the step of applying a vacuum to the channel.
19. The method of claim 11, wherein the buoyant upper chamber comprises a polymeric foam.
20. The method of claim 11, wherein the buoyant upper chamber comprises a plurality of ballast tanks, and further comprising the step of selectively adding water to at least one of the ballast tanks to facilitate orienting the bridge pier during installation.
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No. 11/591,202, filed Oct. 31, 2006, which claims the benefit of Provisional Application No. 60/732,268, filed Nov. 1, 2005, the entire disclosures of which are hereby expressly incorporated by reference herein.
The present invention is in the field of bridge and water platform construction and, more particularly, to support structures for over-water bridges and related structures. The engineering challenges involved in designing and constructing large bridge structures, such as suspension bridges and cable stayed bridges are legion. The bridge structure must have sufficient strength to support itself, the design live loads such as traffic, while also withstanding environmental loads including, for example, wind and other dynamic fluid loads, potential seismic loads, and the like. Typically the bridge structure will be designed to provide both the requisite rigidity to react certain design loads, and a certain amount of flexibility to endure other design loads without catastrophic failure. Moreover, the bridge structure is generally intended to be a permanent structure, and therefore must be designed to maintain its strength and stability over time.
Of course, bridges are often built over bodies of water and rely on support structures that extend into the body of water, and to and into the bed beneath the body of water. Such supports, which may comprise caissons and piers, for example, extend generally from the bed, out of the water to the bridge deck.
Designing suitable support structures for use in estuarial bodies of water having relatively poorly defined sedimentary layers that include significant quantities of fine particles can be very difficult. The support structure generally must provide a very stable support that will transmit very large reaction forces to the ground, while also being flexible enough to withstand loads relating to large episodic events such as seismic events, but must do so in a sedimentary environment that is not conducive to reacting such loads.
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.
A bridge pier is disclosed for supporting an over-water bridge deck. The bridge pier includes a footing defining a footing chamber that is downwardly open, an upper buoyant chamber, and an upright portion that connects the footing and upper chamber. The upright portion also defines a fluid channel that is in fluid communication with the footing chamber. A valve in the fluid channel is configured to be attached to a water ejection pump, or the like, such that the water in the footing chamber can be removed and replaced with air when the footing is resting on the waterway bed. The resulting hydrostatic pressure on the footing facilitates embedding the footing in the bed. The water is displaced with air. Then a valve to the fluid channel is configured to be attached to a vacuum pump, such that the air in the footing chamber can be selectively reduced. The resulting net pressure on the footing further facilitates embedding the footing in the bed.
In an embodiment, a vibratory device is attached to the bridge pier structure and configured to selectively vibrate the bridge pier to further facilitate embedding the footing in the bed. The lower edge of the footing may be chamfered and/or otherwise shaped to promote the embedding process. The vibratory device may optionally be powered by the vacuum source.
In an embodiment, the upper buoyant chamber produces a significant upward force to react the weight of the bridge deck and other loads, for example eighty percent of the weight. The buoyant chamber may be filled with a lightweight material such as a polymeric foam.
In an embodiment of the bridge pier, the upright member comprises at least two telescoping members, such that the distance between the footing and the buoyant chamber may vary.
In another aspect, a method for installing a bridge pier is disclosed. In an exemplary embodiment, the method includes fabricating a bridge pier having a buoyant upper chamber, a footing chamber, and an upright portion defining a channel to the footing chamber, transporting the bridge pier to an installation location, positioning the bridge pier vertically with the footing chamber positioned on a waterbed, and applying suction to the channel such that the pressure in the footing chamber is reduced, such that the footing chamber becomes embedded in the waterbed.
In an embodiment, the bridge pier is fabricated at a location remote from the installation location and is towed in a waterway to the desired installation site.
DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 is a perspective view of a cable stayed bridge in accordance with the present invention, wherein caisson piers are shown in cross section;
FIG. 2 is a side view of a portion of a cable stayed bridge according to the present invention;
FIG. 3 is a front view of the cable stayed bridge shown in FIG. 1;
FIG. 4 is a second embodiment of a cable stayed bridge in accordance with the present invention;
FIG. 5 is a cross-sectional view of the pier for the cable stayed bridge shown in FIG. 4;
FIG. 6 shows a cross-sectional view of a third embodiment of a buoyancy stabilized bridge pier in accordance with the present invention;
FIG. 7 is a flow chart illustrating a currently preferred method for installing a buoyancy stabilized pier in accordance with the present invention;
FIG. 8 is a cross-sectional view of a fourth embodiment of a buoyancy stabilized bridge pier in accordance with the present invention, wherein the upright portion comprises two telescoping members;
FIGS. 9A-9C illustrates a method for installing the bridge pier shown in FIG. 8;
FIG. 10A is a front cross-sectional view of another embodiment of a buoyancy stabilized bridge pier, wherein the upper chamber is formed with a plurality of ballast compartments to facilitate installation;
FIG. 10B is a top cross-sectional view of the bridge pier shown in FIG. 10A.
A partially cross-sectional perspective sketch of a cable stayed bridge 100 according to the present invention is shown in FIG. 1, extending over a waterway 92, in this particular sketch, and, for exemplary purposes only, the estuarial waters of Elliott Bay in the Puget Sound. The cable stayed bridge 100 includes a bridge deck 110 that is disposed over the waterway 92, for at least a portion of its length, some distance above the waterline 93. For example, the bridge deck 110 may be positioned high enough over the waterline 93 to permit nautical traffic to pass therebelow. The bridge deck 110 is supported by one or more tower structures or pylons 102, each tower structure 102 extending upwardly from one of the piers 104. The pier 104 extends into the water, and includes a footing portion 106 that is substantially embedded in the sediment of the waterway bed 91.
Two piers 104 are shown in FIG. 1, although more or fewer piers may be utilized for a particular bridge. The piers 104 in this embodiment have an open, generally caisson-type construction that is open at the bottom. The bridge deck 110 is suspended by a plurality of cable stays 108 that suspend the bridge deck 110 from the tower structures 102. In the embodiment shown in FIG. 1, a bumper assembly 130 is provided around each of the piers 104. The bumper assembly 130 includes a generally annular, buoyant platform 132 that is attached to the pier 104 with a plurality of extendible connecting members 134. The connecting members preferably operate as shock absorbers to protect the pier from any impact loads; for example, resulting from inadvertent collisions by watercraft into the bumper assembly 130.
It will be appreciated that the bumper assembly 130 will not only protect the piers 104 from potential damage from watercraft, floating debris, and the like, passing under the bridge 100, but may also provide a convenient platform for various activities, for example, performing routine bridge inspections or docking, or for conducting other activities not directly related to the bridge 100, such as estuary monitoring programs, recreational activities, or the like. The platform 132 may conveniently be generally polygonal in plan form, for example octagonal, to accommodate such other uses including, for example, to facilitate watercraft docking.
In this embodiment the piers 104 are essentially caissons that extend up from the waterway bed 91 approximately to the water line 93. A substantial portion of the structure of each pier 104 comprises one or more hollow chambers 103 that are filled with air, or alternatively are at least partially filled with a lightweight polymeric foam, or the like, thereby providing an upward buoyancy force, such that the waterway bed 91 does not react all of the forces related to the bridge 100 structure. A watertight lining may be provided covering the walls of the chamber 103, and/or a polymeric foam or a bladder (not shown) may be provided in the chamber 103 to prevent undesired water incursion into the pier 104.
An optional anchor or piling 107 extends from each pier 104, preferably to engage bedrock 94 or other materials more stable and compacted than the material comprising the waterway bed 91.
A side view of the bridge 100 is shown in FIG. 2, and a fragmentary front view of the bridge 100 is shown in FIG. 3 with the bumper structure 130 removed and the bridge deck 110 simplified for clarity in illustrating novel aspects of the piers 104. The piers 104 in this embodiment are generally hollow cylinders that may be formed, for example, of reinforced concrete, each with a footing portion 106 embedded in the waterway bed 91 and the upper portion extending generally to, or beyond, the waterline 93. The footing portion 106 is preferably filled at least in part with local sedimentary materials. The net buoyancy force generated by the pier 104, of course, is approximately equal to the weight of the water displaced by the pier 104, less the weight of the pier 104 itself, and is directed vertically upwards.
As an example, if we assume that the open chamber 103 is a right circular cylinder having a diameter D equal to about 200 feet and an air column height H equal to about 60 feet, then the relevant buoyancy air volume is almost two million cubic feet. Therefore, by Archimedes principle, and assuming a sea water density of about 64 lbm/ft 3, we can easily generate a gross buoyancy force of about 60,000 tons.
The foot portion 106 of the pier 104 that is embedded in the waterway bed 91 is preferably filled with displaced sediment, and therefore does not contribute substantially to the buoyancy force.
The weight of the superstructure of the bridge 100, therefore, may be substantially offset by the buoyancy force on the piers 104, such that the waterway bed 91 does not react all of these very large forces. In a preferred embodiment of the invention, the resulting buoyancy force is selected (by appropriate choice of dimensions of the pier 104) to be approximately equal to the portion of the bridge 100 weight that the pier 104 is designed to support. For example, the net buoyancy force may be designed to be at least eighty or ninety percent of the design supported bridge weight (i.e., the nominal design load of the bridge pier). It is contemplated that water may be pumped into, and/or out of, the chamber 103 to achieve the desired buoyancy force and, optionally, that the buoyancy may be actively controlled by such pumping.
As discussed above, the pier 104 is anchored in place by being partially embedded in the waterway bed 91 and may be further anchored through an optional piling 107 extending down into firmer strata, such as bedrock.
The bridge 100 utilizes a novel pier 104 structure that provides significant advantages over conventional bridge pier structures. In the embodiment shown in FIGS. 1-3, the piers 104 are generally cylindrical, shown illustratively and not by way of limitation, as a right circular cylinder. In particular, the piers 104 are substantially larger in volume than conventional pier structures. The larger overall size of the pier 104 permits the pier 104 to accommodate the watertight chamber(s) 103.
It is contemplated that the piers 104 may be readily installed as follows: First the pier 104 structures may be prefabricated. The piers 104, with sufficient buoyancy to float, may then be towed into position at the desired emplacement. Pumps, valves, or other means for transferring water into the pier 104 may then be used until the pier 104 has a net negative buoyancy. The pier 104 is then guided to the desired position in the waterway bed 91. Hydraulic excavation methods, which are well known in the art, may be utilized to embed the piers 104 in the waterway bed 91, with local sediment occupying a portion of the interior volume of the piers 104. It is contemplated, for example, that a pump may be incorporated into the footing portion 106 that is adapted for hydraulically moving sediment located directly below the footing portion 106. Ports (not shown) may be provided near the upper end of the footing portion 106 to allow some of the sediment to be expelled from the footing portion 106. Once the piers are in place and after, and/or during, construction of the bridge superstructure, in particular those portions of the bridge superstructure that are supported by each pier 104, water is pumped out of the pier 104, for example, by pumping air, other gas, or a lightweight material such as a polymeric foam into the chamber(s) 103, such that the pier 104 produces a net upward buoyancy force that substantially offsets the weight of the bridge superstructure and the weight of the pier 104, but not enough buoyancy to offset the weight of the ballast of sediment that is in the footing portion 106 of the pier 104.
It is noted that many estuaries wherein the present invention may be most suitable have waterway beds 91 comprising relatively fine sediment and similar small-particle matter, such that the piers 104 may be readily installed using conventional hydraulic excavation. It is clearly contemplated that a preliminary bed preparation step may be utilized to clear larger objects away from the emplacement site, if necessary. When a piling 107 is desired, the piling 107, for example, a cylindrical metal shaft, may be first driven into the bedrock 94 using conventional piling installation methods, and the pier 104 provided with an aperture for receiving the piling is lowered to slidably engage the piling 107. The pier 104 may be fixedly attached to the piling 107 after installation, if desired.
It will be appreciated that the buoyancy stabilized piers 104 desirably provide a constant righting force on the piers 104. As suggested above, bridge 100 structure, including the piers 104, may be designed such that there is virtually no dead load on the soil due to the weight of the bridge.
A second embodiment of a cable stayed bridge 150 including a buoyant pier 154 according to the present invention is shown in FIG. 4. The bridge 150 includes a tower structure 152, cable stays 158, and deck 160 that are functionally similar to the bridge 100 described above. In this embodiment the pier 154 includes a relatively large-diameter footing portion 156, a relatively small-diameter middle section 164, and a relatively large-diameter upper portion 166. The footing portion 156, middle section 164, and upper portion 166 form the pier 154.
The footing portion 156 is fully or substantially embedded in the waterway bed 91 and may include an optional piling 167 (not visible in FIG. 4) that extends further into the waterway bed 91 and generally anchors the pier 154 in place. The middle section 164 may be a solid section, or as shown in the cross-sectional view of FIG. 5, may be of tubular construction, preferably including apertures or ports 162, such that the middle section 164 will be substantially filled with water during use. The upper portion 166 comprises a hollow platform that may conveniently be, for example, octagonal in plan form as shown in FIG. 4, or may have any suitable alternative shape. It is believed advantageous to have one or more sides that are relatively straight to facilitate docking watercraft thereto. The upper portion 166 may further include a peripheral bumper structure (not shown) such as the bumper structure 130 described above.
As seen most clearly in the pier 154 cross-sectional view shown in FIG. 5, the upper structure includes one or more chambers 168, 170. The chambers 168, 170 are substantially enclosed, although ports may be provided, for example, to permit inspection or to permit metering in a desired amount of water to achieve a desired buoyancy. The upper portion 166 is sized to provide an upward buoyancy force that substantially reacts the weight loads applied to the pier 154 by the bridge 150 structure. Similar to the pier 104 of the first embodiment, the second embodiment of the pier 154 according to the present invention, therefore, allows the bridge 150 to be designed such that only a small portion of the dead weight of the bridge is transferred to the waterway bed 91. In this second embodiment, however, it should be appreciated that the righting moment on the pier 154 is more positively active because the buoyancy forces are developed at the top of the pier 154.
The enlarged footing portion 156 shown in FIGS. 4 and 5 will help to distribute the loads (static and dynamic) that are transferred to the waterway bed 91 and may be most suitable when no piling 167 is to be used. Alternatively, the footing may be formed as generally the same diameter section as the middle section 164, similar to the first embodiment of the pier 104. The enlarged footing portion 156 embedded in the waterway will resist any overturning forces because to move or overturn the footing would require the movement of a large amount of soil under the footing and/or the creation of a vacuum under the footing, which is impossible because there are no other forces available to do the job.
It is contemplated that the pier 154 primary structures may be formed of any suitable material and, in the current embodiments, are preferably formed primarily from reinforced concrete. The chambers 168, 170 may be lined with a suitably watertight material, for example with a tar, polymeric liner, or the like. Alternatively, the chambers (103 in pier 104, and 168, 170 in pier 154) may be filled with a stable polymeric foam or similar material suitable for the proposed environment, such that the buoyancy of the pier 104, 154 is assured even if cracks occur or the piers 104, 154 are otherwise damaged.
It will now be appreciated that by employing the teachings of the present invention the weight of a relatively massive structure, such as a cable stayed bridge, may be very substantially balanced by buoyancy forces resulting from the pier structure. Therefore, the vertical soil loading at the footing portion may be minimized or substantially eliminated. Moreover, the pier 104,154 will naturally tend towards the upright position, with the substantial portion of the weight of the pier in the footing portion and the net buoyancy force coming from the upper volume. Moreover, it is also believed that the embedded footing portion 106,156 will be substantially homogeneous with the surrounding soil because it is filled with the local sediment, so the tendency for external forces such as tidal currents and earthquakes to move the piers relative to the surrounding soils is minimal.
Pressure-Assisted Bridge Pier Installation
A cross-sectional view of a third embodiment of a buoyancy stabilized bridge pier 200 in accordance with the present invention is shown in FIG. 6. Although not shown in FIG. 6, the bridge pier 200 is suitable for use in cooperation with other bridge structures such as the tower structures 102, 152, cable stayed bridge decks 110, 160, and/or floating dock assemblies discussed above. In this embodiment, the bridge pier 200 includes a buoyant upper chamber 210, a lower footing chamber 230, and an upright portion 220 that connects the upper chamber 210 with the footing chamber 230. The upper chamber 210 defines a buoyant volume 212 that is sized and configured to provide a desired net buoyancy force when the bridge pier 200 is installed. For example, the volume 212 may be sized to provide a buoyancy force that is equal to at least eighty percent of the weight that the bridge pier 200 is intended to support.
It will be appreciated from the disclosure above that in such an exemplary embodiment, the buoyancy force from the volume 212 stabilizes the bridge pier 200 and greatly reduces the forces that must be reacted by the waterway bed 91. The hollow volume 212 may be filled with a gas, for example, air, and may include a sealant layer, bladder, or the like. Optionally, the volume 212 may be filled with a different buoyant material, for example, a polymeric foam. In an exemplary embodiment, the upper chamber 210, upright member 220, and footing chamber 230 are formed from a reinforced concrete.
The lower footing chamber 230 defines a downwardly open volume 232. The distal edge 234 of the footing chamber 230 in this embodiment is chamfered or otherwise shaped or profiled to facilitate embedding the footing chamber 230 in the sediment of the bed 91. Although not shown in FIG. 6, it is contemplated that the distal edge 234 may also be shaped in the circumferential aspect to further facilitate embedding the footing chamber 230. For example the distal edge 234 may be curved or serrated. Alternatively, or additionally, the distal end of the footing chamber 230 may be provided with a flexible skirt, or the like (not shown), that extends outwardly from the footing chamber 230 and lies on the bed 91 to facilitate creation of a vacuum in the footing chamber 230 as discussed below.
The upright portion 220 in this embodiment is a tubular structure and defines a channel 222 that is in fluid communication with the downwardly open volume 232 defined by the footing chamber 230. The upper end 224 of the upright portion 220 is provided with a closeable valve fitting 226 that is configured to be selectively connected to an external apparatus such as a vacuum pump 95A and a water ejection pump 95B. A second valve (not shown) may also be provided. The valve fitting 226 is selectively connected via a hose 96, or the like, to the vacuum pump 95A and to the water ejection pump 95B, which may conveniently be supported on a floating platform 97, such as a barge, boat, or the like. Separate hoses 96 may extend from the pumps 95A, 95B to engage separate valves 226, or a single hose 96 may be provided with suitable switching apparatus to selectively switch the hose between the pumps 95A, 95B.
The water ejection pump 95B may be operated with the second valve opened to remove water from the footing volume 232 and replace it with air through the second valve. Preferably, removal of the water may be facilitated by including a second hose 96A (shown in phantom) that extends from the second valve to the footing volume 232. The vacuum pump 95 is operable to reduce the pressure in the footing volume 232 by drawing air from the footing volume 232 as indicated by arrows 98.
Although in the current embodiment, the buoyant chamber 210, the upright portion 220, and the footing chamber 230 are shown formed unitarily as a single unit, it may alternatively be formed in separate parts and assembled.
Optionally, a shaker or vibratory device 202 may be attached to the bridge pier 200. Although the vibratory device 202 is shown in FIG. 6 attached to an upper end of the upright portion 220 and disposed within the upper chamber 210, the device 202 may be located at any convenient location on the bridge pier 200, including for example on the footing chamber 230. It is contemplated that an optimal location may be selected, depending on the particular application, and that more than one vibratory device 202 may be used. The vibratory device 202 may be powered by the vacuum pump 95A or by a separate power source (not shown). It is also contemplated that the vacuum pump 95A may be configured to produce an unsteady or vibratory suction force to facilitate and encourage embedding the footing chamber 230 in the waterway bed 91.
Refer now to FIG. 7, which outlines a method 250 for installing the bridge pier 200. For convenience and to reduce manufacturing costs, the bridge pier 200 may be fabricated at a location 252 remote from the installation site and, if necessary, transported to a suitable water entry for placement into a desired waterway. The bridge pier is then placed in the waterway and towed to the desired construction location 254. To configure the pier 200 for towing, one or more of the valve fitting(s) 226 may be opened to allow sufficient water to flow into the footing volume 232 and the channel 222, such that the pier will float upright in the waterway with the footing disposed away from the water bed and towed to a desired location. Alternatively, the bottom end 234 of the footing chamber 230 may be sealed and the valve fitting 226 closed prior to placing the bridge pier 200 in the water, such that the bridge pier 200 is oriented generally horizontally as it is towed to the desired location. The footing chamber 230 may then be unsealed and the valve fitting 236 opened to permit water to enter the volume to rotate the bridge pier 200 to an upright position 256.
The hose 96 (or hoses) are then connected to the valve fitting 226 and fluid is allowed to enter the footing chamber 230 as the bridge pier 200 is lowered 258 until the footing chamber 230 contacts the sediment in the bed 91. Optionally, it may be advantageous to temporarily flood the upper buoyant chamber 210 with water to facilitate sinking the bridge pier 200. FIG. 6 shows the bridge pier 200 positioned on the sediment bed 91 and beginning the embedding operation. The bottom end 234 of the footing chamber 230, as it becomes embedded in the sediment 91, will form at least a partial seal. The water ejection pump 95B is connected to the footing chamber 230, e.g., through the valve fitting 226, and the footing chamber 230 is at least partially filled with water prior to evacuating the footing chamber 230, as discussed next. The water ejection pump 95B removes the water and replaces it with air 259. Then the vacuum pump 95A is applied 260 to reduce the pressure in the footing chamber 230. Because of the hydraulic pressures at significant depths, it will be appreciated that a very large net downward force can be generated on top of the footing chamber 230 by evacuating (or partially evacuating) the footing chamber 230.
The downward force is dependent primarily on the size of the footing chamber and the degree of vacuum that is generated in the footing chamber 230. For example, the water pressure at 200 feet is approximately 100 psi. Therefore, a footing chamber 234 having a radius of 100 feet, and substantially evacuated, could generate a downward force of up to F=100*π*(100)2=1,570 tons. This large downward force will tend to force the footing chamber 230 into the sediment. The embedding process may be facilitated by activating the vibratory device 262 while maintaining the reduced pressure in the footing chamber 230. It will be appreciated that although the shaking device 202 is shown near the top of the upright portion 220, it may be located at other convenient locations to optimize the embedding of the footing chamber 230. When the footing chamber 230 has reached a desired position, the vacuum pump 95A and vibratory device 202 are disengaged 264. If the upper buoyant chamber 210 has been flooded, then the buoyant chamber 210 may now be filled with air, or the like, to regain the desired buoyancy.
A unique advantage of the present system is that a pump may be provided to inject a pressurized fluid through the valve fitting 226 to thereby loosen the footing chamber 230 from the bed 91. The buoyant chamber 210 will provide an upward force, such that the bridge pier 200 may be readily disengaged from the waterway bed 91.
FIG. 8 shows in cross-section another embodiment of a bridge pier 300 in accordance with the present invention, which is similar to the bridge pier 200 disclosed above. In this embodiment, the pier 300 includes an upper buoyant chamber 310 defining a buoyant volume 312, a lower footing chamber 330, and an upright portion 320A, 320B connecting the buoyant chamber 310 to the footing chamber 330. The buoyant chamber 310 may be air-filled or filled with a buoyant material, such as a polymeric foam, as discussed above.
The upright portion is formed in two telescoping parts, a first upright member 320A that is fixedly connected to the buoyant chamber 310, and a second upright member 320B that is fixedly connected to the footing chamber 330. The first upright member 320A is slidably disposed over the second upright member 320B, such that the distance between the buoyant chamber 310 and the footing chamber 330 can vary by telescoping the upright members 320A, 320B. The second upright member 320B defines a channel 322 that is fluidly connected to a downwardly open footing volume 332. Optionally, the second upright member 320B may include a stem 321 that extends upwardly from the second upright member 320B and provides fluid communication with the channel 322. A valve fitting 326 at the upper end of the upright portion 320B is configured to attach to an external device such as a vacuum pump 95A, a water ejection pump 95B (discussed above), or a pressurized air source. An optional vibratory device 302 may be provided to facilitate setting the pier 300 in the waterway bed 91.
In this embodiment the buoyant chamber 310 can move in the axial direction relative to the footing chamber 330. This is useful, for example, to accommodate waterways that have significant variations in water height (depth), for example from tidal flows.
The telescoping upright members 320A, 320B provide some advantage for installation, as illustrated in FIGS. 9A-9C. The pier 300 may be fabricated at a location remote from the desired installation site. To tow the pier 300 to a desired location, the footing chamber 330 and second upright member 320B are filled with air and the valve fitting 326 is closed (e.g., any water in the footing chamber 330 may be expelled with the water ejection pump). In the position shown in FIG. 9A, with the valve fitting 326 closed, the air will not escape from the footing chamber 330, and the buoyancy force will raise the footing chamber 330 such that it abuts the first upright member 320A. Optionally, the footing chamber 330 may be provided with a temporary seal (not shown) over the downwardly open end.
When the pier 300 is towed to the desired location, the valve fitting 326 may be opened allowing air to escape therethrough, such that the footing chamber 330 becomes negatively buoyant and sinks to encounter the waterway bed 91, as shown in FIG. 9B. The water may be ejected with the water ejection pump 95B, and the vacuum pump 95 (see FIG. 6) and the vibratory device 302 may then be activated to lower the pressure in the footing chamber 330, and to embed the footing chamber 330 in the bed, as discussed above.
It is also contemplated that the waterbed soil may be conditioned prior to installation of the bridge pier 200, 300. Because of the hydrology of the soil (e.g., the amount of water in the soil) in the footing and under the footing, there will be some advantage to preparing the soil for impact loading that may be anticipated due to future live loads on the bridge footings due to earthquake, wind and sea disturbances, and the like. The soil pressure can be designed to withstand (before liquefying) impact loading due to live loads, including bridge traffic of cars, trucks, and busses on the bridge. In particular, the soil may be compacted (or water removed) to support a design live load by superimposing excessive weight on the soil in and under the footing to offset these anticipated loads.
Soil compaction may be accomplished by preloading the soil to a required density and maintaining that reserve soil pressure for the life of the bridge. On the one hand, additional loading on the footing, for example due to traffic, can be accommodated by changing the air volume in the footing to adjust the buoyancy. However, earthquake, wind, and sea forces can introduce live loads that are short term and sudden. Live loads, if not calculated and accounted for, can cause liquefication and or movement of footing. It would be desirable to accommodate these loads with the soil pressure available at the site by calculating these loads and preloading the soil for these impacts.
This preloading can be accomplished during the installation of the footing and may result in adding depth to the footing height because of the greater compactness of the soil in and under the footing chamber 330. After the footing is installed the preloading can be continued by starting construction on top of the pier with added weight to further remove water from the soil under and in the footing chamber 330. To reduce the amount of water in the soil may take a considerable amount of time. After the preloading is completed, the hydrology of the soil under and in the footing chamber 330 will remain the same because there are no other forces to change the densities of the material. The present invention, for example in bridge piers 200, 300 disclosed herein, provides an apparatus wherein the soil may be preloaded by generating greater vacuum pressures in the footing chamber 330 during the installation.
Another embodiment of a bridge pier 400 in accordance with the present invention is shown in FIGS. 10A and 10B. The bridge pier 400 is similar to the bridge pier 200 discussed above with reference to FIG. 6, and therefore particular aspects of the bridge pier that have already been discussed will not be repeated. The bridge pier 400 comprises a buoyant upper chamber 410, upright portion 420, and footing chamber 430. FIG. 10B shows a cross-sectional view of the buoyant chamber 420 taken through cut B-B in FIG. 10A. In this embodiment, the upper chamber 410 comprises a plurality of individual ballast compartments identified as outer compartments 411 and inner compartments 412. Each of the ballast compartments 411, 412 is provided with a valve 413 to permit.
The individual valves 413 are operably connectable to a pump or vacuum pump such as 95A, 95B described above, such that the ballast compartments 411, 412 may be selectively filled (or partially filled) with water, and/or water can be removed therefrom. It will be appreciated that selective control of the amount of water in the ballast compartments 411, 412 provides a convenient means to control the vertical alignment of the bridge pier 400, to facilitate installation.
It is further contemplated that the selective control of the ballast compartments 411, 412 may assist in the installation by providing a mechanism for adjusting the upright orientation of the pier 400 during installation after it is partially embedded in the waterbed; for example, to aid in further embedding the footing in the soil.
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.
Patent applications by Roger Patten, Burien, WA US
Patent applications in all subclasses PIER