Patent Publication Number: US-6659686-B2

Title: Precast modular intermodal concrete shapes and methods of installation to form shoreline stabilization, marine and terrestrial structures

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is related to the prior application U.S. Ser. No. 08/285,052 of applicant Veazey et al., filed Aug. 3, 1994, now U.S. Pat. No. 5,697,736, issued Dec. 16, 1997, which is incorporated herein by reference in its entirety, and is a divisional of Veazey&#39;s U.S. Ser. No. 09/776,971, filed Feb. 5, 2001 now U.S. Pat. No. 6,491,473. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This application pertains to precast concrete structures of various sizes and shapes which are suitable for installation as integrated systems to form seawalls and various shoreline reinforcement systems for limiting shoreline erosion by rivers, lakes, oceans, sounds and other major bodies of water, as well as terrestrial structures for terracing, dams, bridges, buildings, etc. 
     2. The patent referred to above provides a summary of relevant prior art. While many techniques have been developed for reinforcing shorelines, as described in that patent and various publications of the U.S. Army Corps of Engineers, there is still considerable room for improvement. Applicant&#39;s company Seament Shoreline Systems, Inc. of Virginia and its subcontractors have completed several shoreline installations using the components and methods disclosed in the above patent. The Corps of Engineers publication “LOW COST SHORE PROTECTION . . . a Property Owner&#39;s Guide” discloses at page 154 the use of precast open concrete boxes filled with sand to form waterfront sills to retain perched beaches. U.S. Pat. No. 5,697,736 discloses in columns  8 - 9  the use of precast concrete boxes as alternatives to Double “T” units (discussed below) for constructing pier-groins extending seaward from a seawall and for use in forming underwater and near-shore) breakwaters. Columns  12 - 13  and FIGS. 20 to  25  discuss the use of such concrete boxes to form floating pier assemblies. 
     Catalogs of Admiral Marine Co. (Staten Island, N.Y., New Orleans, Oakland, Calif. and Chicago) and Peck &amp; Hale (West Sayville, N.Y. and Kowloon, HONG KONG) disclose various metal fastening devices which could be employed to connect certain components of the present invention to form structures. 
     Changing weather patterns and rising sea levels have increased the risk of shoreline damage from hurricanes and other storms, while environmental and zoning laws in many cases make it very difficult to rebuild shoreline structures which are destroyed or damaged. Accordingly, it is prudent for both private owners and governmental bodies to take timely steps to protect waterfront installations from foreseeable damage. Normally, large stone rip-rap revetments, groins or breakwaters have been used for such protection. However, these methods require that a large total mass of materials be transported to the site. Such rocks are difficult to handle, cannot be interconnected or floated into place and are not easily relocatable. Furthermore, such rocks are not amenable to intermodal transport or use in a modular system. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide easily transportable construction components which can be used to control shoreline erosion. As another object, such components should be provided in sizes, shapes and proportions which are compatible with existing trucks, railcars and maritime transportation modes as well as adapted to existing materials handling equipment. As a further object, the components should be transportable in segments so that they can be moved into positions for installation through crowded beachfront areas, by land, water or aircraft such as heavy lift helicopters, blimps or dirigibles. 
     Another object of the invention is to provide such construction components as partially-closed containers which are light in weight but can be filled with available liquid or solid materials at the installation site to substantially increase their mass at little cost. A further object of the invention is to provide construction components which can be filled with solids, gases or liquids to increase their masses when installed as part of a structure, simultaneously serving as sealed storage containers for such materials for later use. 
     An additional object of the invention is to provide construction components which have the largest masses practicable when filled with ballasting material and installed to form structures. Maximizing the mass of such components is desirable to equip the structures to resist the large forces generated by storm waves, currents, floods, mudslides, earthquakes and other natural disasters. Such maximizing of mass can have similar applications in combat engineering, where enemy artillery, bombardment and demolitions may be encountered. The underlying physical principle is expressed by the equation F=ma, i.e. force equals mass times acceleration. The forces generated by mudslides, floods, hurricanes and large storm waves, currents, etc. can be very strong. (See calculations in columns  17 - 20  of the patent referred to above.) However, if the resisting mass of an object is very large (especially in comparison to the surface area against which water pressure is exerted), the resulting acceleration of the object in response to a large force can be relatively small. 
     Thus, it is an object of the invention to provide construction components which have ratios of surface areas and installed masses to successfully resist the forces which can be reasonably foreseen for the installation area. A further object is to provide such components which can be connected together when installed to form a structure, thus providing very massive structures which will successfully resist the worst forces of nature with very little acceleration response or damage. 
     Still another object of the invention is to provide intermodal sets of precast concrete boxes which can be used as construction components for various civil, marine, commercial or military construction projects. Such components could be connected together to form causeways, fixed or floating bridges, dams, drilling rigs, floating or fixed airport runways or helicopter pads, temporary or permanent shipping ports, temporary military or naval facilities, “container ships”, relocatable modular waterfront structures such as houses, and many other applications. 
     Another object of the invention is to employ recyled materials in the concrete mix where possible to reduce material costs as well as to help protect the environment. For example, fly ash from power plants can be successfully used in various concrete mixtures for casting the construction components. Used tires can be used as gasket or cushioning material to be placed between the precast constructions components in some installations. 
     Still another object of the invention is to provide methods of installing precast concrete boxes in underwater positions by transporting them on floating vessels and/or floating them into approximate position and sinking them into their final installed positions. A related object is to provide vessels which are suitable for transporting such boxes, either as deck cargo or as a floating component of the vessel itself. 
     Yet another object of the invention is to provide shellfish habitats based upon precast concrete boxes which will allow shellfish to grow in underwater areas separated from pollution or silting and facilitate convenient and effective harvesting of the mature shellfish. 
     In accordance with the present invention, improved versions of the L-members of the previous patent (having vertical walls, horizontal footers, vertical keys protruding below the footers and an angular splash plate protruding from the member directly opposite the footer), with at least one substantially vertical passage penetrating the splash plate and key, with an upper inlet and a lower outlet to facilitate setting the L-members in place by use of fluids comprising water under pressure emerging from the lower inlets of the passages. These L-members can be further improved by adding accessories including: 
     a) precast concrete components comprising channels adapted to form a cap atop the vertical wall portion of an L-member and mechanically attached thereto, and sections extending horizontally from the channels when the cap is in place, forming horizontal support surfaces substantially perpendicular to the vertical wall portion; 
     b) precast concrete components which are fastened to the upper surfaces of the horizontal sections described above, approximately perpendicular thereto, and either affixed thereto by mechanical attachments or precast as a unit therewith; 
     c) longitudinal precast concrete components having channels in each end, with one channel adapted to fit the top of the vertical wall portion of the L-member and emplaced thereon, with the other channel being adapted to accommodate a horizontal railing member which is placed atop the longitudinal members and fitted in the channels thereof to form a railing atop the vertical wall portion of the L-member; 
     d) precast concrete channel components having the cross-section of a squared letter “U”, with the groove adapted to fit the top of the vertical wall portion of the L-members, these channel components being emplaced atop the L-members to form a cap atop the vertical wall portion thereof; 
     e) precast concrete components forming a step cap, comprising a portion to be attached to the upper portion of the vertical wall portion of an L-member, a portion extending downward therefrom at an obtuse angle to the vertical, and forming at least two stair steps extending from the top of the vertical wall portion to the base of the L-member, normally comprising bracing means extending between the underside of the stair steps and the splash plate and/or vertical wall portion of the L-member to provide support for the stair steps. 
     As disclosed in the previous patent, these improved L-members can be assembled to form structures such as sea walls or bulkheads, and used in conjunction with precast concrete components placed perpendicular to such a sea wall as groins to form shoreline reinforcement systems. A variety of precast concrete components can be used to form such systems, including T-walls, pi-walls, precast concrete boxes and the like, and concrete mat sections can be used to fill in horizontal spaces between such groins. 
     Precast concrete boxes of various types, including those disclosed in the previous patent and new versions described below, can be used to form many structures, including sea walls or bulkheads and shoreline reinforcement systems based thereon, which may include such precast boxes and/or other precast components discussed above to form groins, horizontal sections, breakwaters and the like. Precast concrete boxes can also be employed to construct waterfront boathouses, either with solid foundations or floating bases, and modular structures suitable for dwellings, offices or shops. 
     Novel systems of precast concrete boxes are provided which generally have the overall form of rectangular parallelepipeds. The boxes can be enclosed on all sides and provided with means for flooding with water and subsequently expelling the water using air pressure or pumping means to raise the sunken boxes. Alternatively, they can include openings such as holes or slots, as disclosed in the previous patent. These and even the precast concrete boxes previously disclosed can be produced in sets, including at least two different sizes and sets of proportions which permit the boxes to be conveniently shipped together by intermodal means of transport and also assembled together to form various structures. The boxes have at least one dimension adapted to fit conveniently into at least one transportation mode such as truck trailers, rail cars and container ships, with a set including a plurality of boxes having at least two different combinations of dimensions and/or proportions. The smaller boxes have at least one dimension which is a whole number fraction of the corresponding dimension of the largest box of the set, which might be termed the “master box”. The boxes can be divided by horizontal or vertical partitions into at least two separate inner compartments which can be independently flooded or blown, with valves adapted to equalize air pressure and/or liquid contents between these compartments. In some embodiments, these boxes can have removable concrete tops. 
     An embodiment of the enclosed boxes described above which is suitable for constructing bridges and the like has the overall form of a rectangular parallelepiped with five surfaces substantially enclosed, the sixth surface having the largest dimension of the box and the two surfaces adjacent thereto being cut out to form a channel adjacent to the sixth surface when it rests upon the ground. The portion of the box below such cutouts can be left open or joined with an enclosure to seal the box on all sides. Inlets can be provided to fill such boxes with sand, water or the like. 
     Various types of precast concrete boxes of the invention (and even the prior art) can be assembled to form waterfront structures such as boathouses, either on solid foundations or on floating assemblies of the boxes. With solid foundations, the cutout boxes described above can be emplaced upon the bottom to allow for the flow of water currents. 
     The enclosed precast concrete boxes of the invention can be interconnected together by mechanical means to form bundles or assemblies like log booms to be towed or otherwise transported over water. Further in accordance with the invention, such interconnected groups of concrete boxes which form a large rectangular mass can be transported by a self-propelled vessel for transporting floating objects which comprises separate bow and stern sections adapted to be fastened together using mechanical means to form the vessel alone. When used for transporting such assemblies of boxes (or other interconnected groups of floating objects such as logs, containers, tanks, floating drydocks or the like), the two sections of the vessel are separated and connected to the ends of the group of boxes to form a “stretched” vessel in which the group of boxes forms a midship section. The vessel is provided with conventional propulsion systems (in the stern section), thruster propulsion units to aid in maneuvering, anchors and power supplies for their operation and at least one crane for unloading and emplacing the boxes or other cargo at destination. 
     Further in accordance with the invention, certain embodiments of the precast concrete boxes are used to form shellfish habitats, and are preferably cast from concrete comprising crushed bivalve shells. Oyster shells are preferred, but any calcareous shells can be used, such as clam, mussel or conch shells. The boxes can have holes and/or slots in the walls, which can be temporarily plugged with knockout sections to facilitate sinking the boxes in the water, and removable concrete tops. The tops can include various projections on one side (which is emplaced inside the box during transport, then reversed to face outward and upward during installation) to provide optimum surfaces for young shellfish to adhere to. The projections can have the form of cylinders, conical sections or rectangular parallelepipeds, cast integrally with the tops or mechanically affixed thereto. The tops can also be cast with broken bivalve shells (such as oyster shells) adhering to the outer surface, to provide natural shell surfaces for the young shellfish to adhere to. Means are provided for removing and hoisting the lids of such shellfish habitats for harvesting, and/or for expelling the water within enclosed versions of the boxes and floating and/or hoisting them to the surface. 
     In another embodiment, a shellfish habitat comprises a rectangular meshwork container comprising a rigid frame and meshwork enclosure surfaces to retain therein various objects which may provide appropriate shellfish habitat. The container has a shape and size suitable for emplacement atop precast concrete boxes as discussed above, and to accept precast concrete tops fitted with projections for shellfish culture, also as described above. The container and/or cover are fitted with cables or other mechanical devices for hoisting out of the water for harvesting of shellfish. 
     The precast concrete boxes of the invention can be installed in the water along a shoreline by sealing all inlets below the expected waterline of the installed boxes, placing the boxes in the water and floating them into position, then opening sufficient water inlets and air outlets to allow the boxes to sink into their assigned places. In preferred embodiments, these inlets and outlets can be opened remotely, and guidance can be provided to the boxes while they are being sunk into position. A group of such boxes can be interconnected and emplaced beneath the water to form a submerged breakwater or reef by positioning the connected boxes atop a flat deck of a vessel, emplacing an anchor on the bottom near the planned installation position and attaching same to a cable slidably connecting the boxes on deck, launching the boxes into the water while the vessel proceeds forward away from the anchor, then maneuvering the boxes into end-to-end contact and clamping the resulting string of boxes into place on the cable, placing the resulting floating string of boxes into position directly above the planned installation position, and finally, sinking the boxes while guiding them into final position by securing the forward end of the cable to a second anchor at the opposite end of the string from the first anchor and applying tension to the cable from the vessel. 
     The vessel used can be a barge, a vessel with a bow door and ramp (such as Navy landing ship tank, landing craft mechanized, landing craft vehicle and personnel and the like) or a vessel with an after well deck affording access to the water for floating boxes directly into the water (such as a Navy landing ship dock). A container ship with a flat deck and cranes to hoist the boxes from deck level to water level can also be used. 
     Additional objects and advantages of the present invention are described in, and will be apparent from, the following detailed description of preferred embodiments together with the drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a prior art “L-wall” from U.S. Pat. No. 5,697,736. 
     FIG. 2 is a sectional view of an inverted T-shaped unit from the same patent. 
     FIG. 3 is a sectional view of a conventional “double T” or pi-shaped unit from the same patent. 
     FIG. 4 is a perspective view of precast concrete boxes from the same patent. 
     FIG. 5 is a side view of an improved “L-wall” for use in the present invention. 
     FIGS. 6 and 7 are sectional views of accessories in use with the L-walls of FIG.  5 . 
     FIGS. 8 and 9 illustrate further refinement of the L-walls of FIG.  5 . 
     FIGS. 10-12 are plan, side and end views of improved precast concrete boxes of the present invention. 
     FIGS. 13A,  13 B and  13 C are plan, side and end views, respectively, of intermodal boxes of the invention arranged on deck for transport. 
     FIGS. 14A and 14B are end and plan views, respectively, of an underwater breakwater assembled of such boxes. 
     FIGS. 15-17 are plan, side and end views of such precast boxes with provisions for sinking same in water and raising them thereafter. 
     FIG. 18 is a side view of a precast concrete box of the present invention floating near the surface of a body of water. 
     FIG. 19 is a top view of a series of precast concrete boxes connected together to form a structure. 
     FIG. 20 is a side view of a precast concrete box of the invention which has been sunk to the bottom in a body of water. 
     FIGS. 21-23 illustrate anti-scour plates for use with the precast concrete boxes of the invention. 
     FIGS. 24 and 25 illustrate connecting devices for use with the precast concrete boxes of the invention. 
     FIGS. 26-29 illustrate the employment of various connecting devices to connect such boxes. 
     FIG. 30 is a sectional view of a quick connection for an air hose inserted into a hole in the tank which can be employed to refloat the precast concrete boxes of the invention. 
     FIGS. 31-33 are end, plan and side views, respectively, of a waterfront boathouse constructed with precast concrete boxes of the present invention, resting upon the bottom. 
     FIGS. 34 and 35 are end and plan views of a larger floating boathouse constructed using three large precast concrete boxes of the invention. 
     FIGS. 36 and 37 are plan and side views of a conventional fixed boathouse using piles surrounded by concrete boxes to protect the boathouse from ice. 
     FIGS. 38-40 are side, top and end views of a modified precast concrete box of the invention which is suitable for building bridges. 
     FIG. 41 is a top view of a shoreline reinforcement system assembled from precast concrete boxes of the present invention. 
     FIG. 42 is a side sectional view of the shoreline system of FIG.  41 . 
     FIGS. 43-45 are side views of a ship designed to incorporate a module assembled of precast concrete boxes of the invention as the parallel midbody of the ship in order to transport same. 
     FIGS. 46-48 are side views illustrating the launching of floating precast concrete boxes of the invention from a ship or barge and the sinking thereof to form an underwater structure. 
     FIGS. 49 and 50 are end and plan views, respectively, of a dwelling structure assembled from precast concrete boxes. 
     FIGS. 51 and 52 are perspective views illustrating shellfish habitats based upon precast concrete boxes of the invention, with two types of removable concrete tops. 
     FIGS. 53 and 53A are perspective views illustrating another version of shellfish habitat with removable top, including means for hoisting the assembly from underwater. 
     FIG. 54 illustrates a seawall and beach reinforcement system including a seawall, at least one groin built of inverted “T” structures, at least one row of inverted “T” structures parallel to the seawall, and flexible cloth-concrete cable or chain assemblies emplaced in conjunction with same. 
     FIGS. 55 and 56 illustrate a seawall and reinforcement system designed for installation along the Potomac River shoreline in Virginia, including groins perpendicular to the seawall. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It should be understood that the following description of the presently preferred embodiments of the present invention is merely representative of many possible embodiments and thus is not intended to limit the scope of the invention. In the following description, like structures will be referred to by similar numerical designations. 
     Referring now the the drawings, FIG. 1 is a sectional view of an L-wall as disclosed in the earlier patent. FIG. 1 illustrates an L-shaped structural member ( 2 ) of the above patent, intended for use in retaining walls, seawalls and the like. Vertical wall or stem portion ( 4 ) is substantially perpendicular to footer ( 6 ), and vertical key ( 8 ) extends below the lower surface of the footer, essentially in line with the vertical wall portion. Angular splash plate ( 10 ) protrudes from wall( 4 ) opposite footer ( 6 ), forming an obtuse angle () downward from the wall and forming an acute angle (β) with the plane of the footer base. The thicknesses of the vertical wall and footer portions can vary, being thickest near their intersection where stresses are greatest and tapering toward their extremities. For optimum strength, such structural members are cast with fiber or metal reinforcing bars (rebar) ( 12 ) emplaced vertically and horizontally as shown as shown to increase the strength of the member in operation. Holes ( 14 ) are preferably formed in the vertical wall and footer portions to provide drainage for liquid collecting behind the retaining wall or seawall. Holes ( 16 ) can also be placed to facilitate handling and temporary interconnection of the L-members as well as drainage. 
     The L-shaped members and other components disclosed herein can be precast by conventional methods known in the art, and in some cases existing commercial components can be utilized to assemble the novel shoreline reinforcement systems of the invention. When the components are to be exposed to salt water, it is preferred that all rebar be at least about 2 inches from any surface of the cast bodies. Fiber reinforcement should be included in the concrete for strength, a relatively high proportion of Portland cement should be used in the mix, and the forms should permit a smooth finish to be obtained on the finished molded objects. The forms should be subjected to vibration, using commercially available mechanisms, after the molds are filled to consolidate the concrete and minimize voids or defects. Preferably, fly ash and other recycled materials should be used in the concrete to the extent it is physically and economically beneficial. 
     FIG. 2 is a sectional view of an inverted T-shaped unit as disclosed in the earlier patent. FIG. 2 illustrates a cross-sectional view of an inverted “T” wall or structural member ( 50 ) as disclosed in U.S. Pat. No. 5,697,736, having a vertical wall ( 52 ) and a symmetric base or footer ( 53 ). Such components can be cast of concrete, preferably containing rebar reinforcement ( 54 ) as illustrated above for the “L” walls, in various sizes and proportions to suit the application. For example, for shoreline reinforcement systems exposed to water, such “T” walls can range from about 2 to about 6 feet high and from 2 to about 6 feet wide, the ratio of height to width of the base ranging from about 0.6 to about 1:1. The sections can range from about 6 to about 16 feet in length. Particularly when the installed structures will be exposed to tidal flows, strong currents, surf or pack ice, the width of the base and the lowness of the center of gravity should be emphasized to minimize the risk of tipping. A plurality of holes ( 56 ) can be formed in the wall to facilitate handling, some sand and water bypass and interconnection. Similar holes in the base permit the use of pins, harpoon type anchors or stakes ( 58 ) to secure the units to the beach. 
     In the present systems, these inverted “T” walls are used to form groins extending seaward from a seawall or bulkhead, and may optionally be used in rows parallel with the seawall as well, as part of a system to reinforce the shoreline, form a “perched beach” or the like. Such groins are typically installed substantially perpendicular to the seawall and are used in pairs or greater numbers. The spacing and length of such groins must be carefully selected to encourage sand, gravel and other material to collect on the beach. In some cases the effects of groins, seawalls and other beach reinforcement systems can be difficult to predict even after careful analysis. If necessary, the “L” walls and inverted “T” walls described above can be disconnected and relocated. Such analyses are beyond the scope of the present disclosure, but some guidelines may be found in “Low Cost Shore Protection”, published by the U.S. Army Corps of Engineers. 
     FIG. 3 is a sectional view of a conventional “double T” or pi-shaped unit from the earlier patent. FIG. 3 illustrates in cross-sectional view conventional “Double T” cast concrete structural members ( 66 ) which may be used in systems of the present invention. Such structural members are used in constructing parking garages. The lengths of such units can range from about 20 to about 60 feet, with length limited mainly by the difficulties of handling such heavy components over the road and along shorelines where they are to be installed. Because of their dimensions, the two tapered upright sections ( 68 ) joined to the flat base portion ( 69 ) give the appearance of two “T” shapes joined side-to-side. The units are also known as “pi” units because of their resemblance to the Greek letter pi. 
     FIG. 4 is a perspective view of a precast concrete box which was disclosed in the earlier patent for use in constructing breakwaters and the like. As an alternative to arrangements of inverted double “T” units to form pier groins, precast concrete boxes of various sizes can be used for various site-specific conditions. For instance, precast septic tank forms come in various sizes, e.g. approximately five feet wide by eight feet long and three feet depth, with walls four inches thick. Concrete boxes made from these existing forms can be used with modifications of openings, stronger and more waterproof concrete, reinforcements, connecting devices and the like, being sunk in position to form the base of pier-groins and the like and filled with water, rocks, sand or rubble. However, preferably they are adapted as shown in FIG.  4  and disclosed in U.S. Pat. No. 5,697,736, where the box ( 81 ) has four sides which have been perforated or slotted with circular holes ( 83 ) and/or rectangular slots ( 85 ) of a few inches diameter or width. This will make the boxes easier to sink and anchor in position. As with the inverted T units shown in FIG. 2, the boxes can have holes formed in the bottom to accommodate anchoring stakes of rebar, screw anchors such as shown in FIG. 24 of the previous patent, or other suitable anchoring means. Preferably plugs are used in the casting molds to form holes ( 83 ) or slots ( 85 ) which are sealed by thin layers of concrete. Such holes will also make it easier to sink the boxes in the water, as the thin “knockout” portions of the concrete can be punched out once the boxes have been floated into position. Once sunk, of course, it is difficult to refloat such boxes. 
     Such perforated and/or slotted boxes can serve an additional function beyond anchoring the foundation of a pier groin or other component. Since waves striking the surfaces of such boxes will be partially interrupted or deflected and partially absorbed by passage through at least one side of the box (i.e., the perforations or slots), their force will be at least partially dissipated. The water inside the boxes remains largely restricted or “dead” during the time periods of the waves. Thus, such boxes may be used as “wave degeneration cells” as components of the foundations of pier-groins, groins parallel or perpendicular to the shoreline, or even breakwaters. The dimensions and arrangement of the boxes as well as the dimensions and locations of their perforations and/or slots are of course selected to suit expected conditions. Additionally, these boxes with openings could also serve as protected nurseries for baby fish, crabs, oysters, etc. Such boxes, and other precast concrete boxes described below, can also be used on the sea bed to support racks, baskets or other substrates above siltation levels for shellfish to adhere and grow. Providing such elevated shellfish beds may permit the shellfish to be placed at the optimum depth of water to avoid pollution and siltation and obtain maximum benefit from currents, sunlight and nutrients. The perforations and/or slots should not extend too close to the base, where they might hinder retention and/or accumulation of anchoring material. 
     Such a breakwater can be built by anchoring a linear array of the precast concrete boxes so as to form a wall either, e.g., five or eight feet wide, then stacking the units as shown in FIG.  4  and lashing or otherwise fastening them together to form a breakwater of suitable height. At least the lower layer of the boxes should be at least partially filled with sand, rock or other anchoring material, but vacancies left in some of the boxes will provide shelter for marine life, thanks to the perforations and/or slots which allow easy access. 
     FIG. 5 is a side view of an improved L-wall in accordance with the present invention. Reinforcing bars, drain holes, securing holes and the like can be included as shown in FIG. 1, and are omitted here for clarity. Fillets  15  can be formed of concrete between wall  4  and footer  6  and/or splash plate  10  to increase the strength of the unit and provide more cover for the steel reinforcing bars. L-wall  2  is shown with vertical key  8  placed in a concrete culvert or “trench”  9  of various depths which has been dug, levelled and backfilled to facilitate installation of the L-wall. Pipe  13  is cast into the portion of the L-wall between splash plate  10  and footer  6  to provide a channel for pressurized water (or water-air mixtures) to be used for “jetting” the key  8  into place in sand and/or for flushing the key trench. Only one pipe  13  is shown in this view, but a series of pipes are to be cast into the L-wall along its length to facilitate jetting the unit into the sand which has been cleared of rock and debris. Any suitable arrangement of hoses and/or manifolds can be used to introduce water and/or air through pipes  13  during “jetting in” the L-wall. Such “jetting in” procedures are described in columns  9 / 10  of U.S. Pat. No. 5,697,736. Another series of pipes  11  are included in trench  9 , also to assist in jetting the trench  9  into the sand. Expanded metal or heavy wire mesh is bent into lengths of rectangular reinforcement  17  which are open at one end and cast inside trench  9  to form a reinforcing structure. 
     Improved L-wall  2  is shown here with a precast concrete tip cap  20  placed atop the vertical or stem portion  4 . Tip cap  20  is formed much like a household rain gutter, with sides  21  and bottom  23  defining channel  25 , and is preferably cast in appropriate lengths to cover the entire length of the L-wall, although they can also be formed in shorter units. Among other uses, such caps  20  can be placed atop a series of L-walls to hold the tops of their stems  4  in alignment. Also shown schematically with this improved L-wall  2  is a set of precast concrete steps  22  cast with cap  20 , a precast body incorporating a series of right angles which can form steps when aligned with one side of stem  4  of L-wall  2 . The steps braced on both sides by solid sidewall units  27  which are cast on each side of the step ends and contact L-wall  2  on the seaward face, respectively, of stem  4  and splash plate  10 . Such a step installation can be conveniently used by persons to climb to the top of the L-wall, which may form a portion of a seawall, bulkhead or the like. Such steps could be placed near the upstream or upcurrent side of a groin, where they would be covered by more sand on the lower steps for stability. 
     FIG. 6 is a side view of another accessory for L-walls  2 , namely a precast concrete sidewalk cap  30  having a channel  32  formed therein to fit atop stem  4  of L-wall  2 , a cantilever support  34  and a flat walking surface  36  extending to one side of the unit. When L-wall  2  is built into a seawall or the like and the landward side is filled in, such sidewalk caps  30  can be installed atop the L-walls to provide a flat surface suitable for use as a sidewalk or the like. Furthermore, precast concrete terrace retaining walls  38 , having a slightly tapered rectangular cross-section, can be cast into such a sidewalk cap  30  to extend the height of the L-walls. This is also convenient for forming a low wall separating a sidewalk or walkway from the seaward side of a seawall constructed of L-walls, if not backfilled. Optionally, retaining walls  38  could be separately cast and mechanically attached to sidewalk cap  30 . In addition to providing a flat surface atop a seawall or the like which can serve as a sidewalk, sidewalk cap  30  covers the area immediately behind the L-wall to prevent scour from waves or rain. Terrace retaining walls  38  can be backfilled to provide retaining walls atop sidewalk cap  30 , or left freestanding as safety rails. 
     FIG. 7 shows a side view of the top of stem  4  of an L-wall  2  which has been topped with a railing cap  40 . Railing cap  40  has a broadened lower end containing a channel  42  adapted to fit the top of stem  4  (as with the sidewalk cap discussed above), and is secured in place by slipping channel  42  over the top of stem  4 . Cap  40  can be mechanically fastened to stem  4  by any suitable mechanical means, such as pins or bolts  41  passing through holes  43  in both the base of cap  40  and stem  4 . A cantilever section  45  can be added to cap  40 , either cast integral therewith or attached by any suitable mechanical means, to add strength and provide a narrow walkway landward of cap  40 . As with the sidewalk caps, these railing caps can be fabricated in various lengths, and can be used to keep the tops of the stems of adjacent L-walls in alignment in addition to providing a railing or terrace wall atop an array of L-walls. Railing caps  40  can also be fabricated in much shorter lengths or as posts (i.e., a foot or so in length and width), with railings (not shown) inserted through holes  44  in adjacent units and mechanically secured in place. Optionally, for ornamental and personal comfort purposes, an ornamental railing  46  can be secured to the top of such railing caps by inserting mechanical connection strip (or pins)  48  into groove or holes  49  in the top of railing cap  40 . Railings  46  can be made of materials such as wood, metal and polymeric compositions, preferably those which can be made smooth to the touch and durable when exposed to the elements. 
     The sidewalk, terrace and railing caps described above can be precast concrete as discussed in U.S. Pat. No. 5,697,736, and can be connected together if desired, by mechanical devices also disclosed in that patent. 
     FIG. 8 shows a side view of the improved L-wall of FIG. 5, with additional features. Holes  25  are included in the stem  4  of the L-wall during casting, to provide for drainage through the L-wall from the landward side to seaward. These holes can be plugged if necessary (e.g., when L-walls are used to form a dam or dike) with solid plugs  27  (formed of any durable polymer such as polyvinyl chloride), or hollow plugs retaining in place a filter cloth soil retainer  29 . Filter cloth retainers  29  are used in lieu of a larger continuous piece of filter cloth or geotechnical material to cover holes  25 . If such filter cloth or geotechnical fabric should deteriorate over time, additional solid or hollow plugs could be inserted from the accessible seaward side of the L-wall. Perforated metal or polymeric fittings  31  are cast into stem  4  and/or footer  6  at each end of the L-wall to provide means for interconnecting the L-walls via bolts or other suitable mechanical fasteners. Drain holes  14  can be left open or plugged with solid plugs  27  or hollow plugs with filter cloth, as described above. 
     The improved L-walls of the present invention can incorporate the extended angular splash plates, disclosed in column  6  of U.S. Pat. No. 5,697,736 and the figures cited, which are incorporated herein by reference. 
     FIG. 9 provides a top view of the stems  4  of two L-walls  2  which are to be fitted together. In A, the edge of the stem  4  at the right is bevelled so as to fit into a corresponding groove in the stem  4  on the left, backed by filter cloth for drainage or filled with bead caulk  33  or other suitable material to be inserted between their surfaces to provide a good seal between the two L-walls if used as a farm pond dam or the like. The L-walls of the present invention can be cast with one end of the stem bevelled and the other grooved, as described, to facilitate such fitting together during installation. At B, the stem  4  at right has a trapezoidal projection  37  which fits into a corresponding groove  39  in the other stem  4 . Caulking material  33  can be used as in A. The C version uses a dovetail method, with projection  41  and groove  43  in the two stems  4 , to provide a more secure fit. One L-wall must be lifted to join the two stems in this case, and caulking is optional. 
     FIGS. 10 to  12  are plan, side and end views of precast concrete boxes of the invention which can be employed on shorelines, underwater and in intertidal zones. The boxes  90  take the form of a simple hollow box of parallelepiped form with sides, ends, bottom and open top, which can be optionally capped with a tight-fitting top  92 , held in place by gravity or optional mechanical fasteners (not shown here). Top  92  is omitted in FIG. 10 for clarity. Holes  94  are provided in the lower corners of the sides and ends to be used for connecting cables or rods (not shown here). Vertical holes  96  are provided in each corner of the box at the top to assist in securing top  92  when used or for mechanical connecting devices when the boxes are stacked or secured to the bottom. A low sill  98  on the inside bottom divides the box into halves for connecting overlapping boxes alongside, and holes  99  extend laterally from side to side through this sill to accommodate connecting devices such as cables or rods and also handling means. The boxes shown here are intended to be fluid tight (when capped), in contrast to the boxes of FIG. 4, which are open to the water in which they are immersed. The boxes can be positioned adjacent each other (side-by-side and/or end-to-end) and fastened together using holes  94 ,  96  and  99  and various mechanical fasteners. When interconnected side-by-side, the boxes are preferably positioned in overlapping fashion (with the ends of two boxes positioned adjacent the center of a third box) to form a stronger structure. These boxes can also be stacked as shown in FIG.  4 . 
     These boxes and those described below are “intermodal” shapes which can be conveniently handled and shipped by at least two modes of transportation, including trucking, railcar and surface water transportation including container ships and barges. That is, they have dimensions (length, width, height) which will permit them to conveniently fit into the allowable spaces in such transport media, either singly or in combination. For example, currently standard containers measuring eight feet square and either twenty or forty feet long can be easily transported by ship, rail and trucks. Furthermore, these boxes can be produced as sets of at least two different sizes, having proportional dimensions which facilitate their use in standard size transportation media and together to form structures such as seawalls and other shoreline reinforcing systems of various sizes. 
     For example, FIGS. 13A,  13 B and  13 C provide top, side and right end and plan views, respectively, of boxes of several dimensions positioned on deck for transport in a space forty feet long and 24 feet wide, with boxes stacked to a uniform height of eight feet. The dimensions of boxes of types A through H are indicated in the legend. Clearly, where boxes having dimensions as large as eight feet square by forty feet long can be conveniently transported, a number of boxes having at least one dimension a suitable fraction (e.g., one half) of these can be assembled to fill the same space for transport. Thus, for an intermodal set of boxes, the maximum dimensions are determined by the maximum space available on deck and/or inside a truck trailer or railcar, and smaller boxes can be designed with similar proportions but having at least one dimension which is, e.g., one half or one third of those of the largest box of the set. In other words, the smaller boxes are produced with one, two or three dimensions which are a fraction (preferably divided by a whole number) of the corresponding dimensions of the largest box of the set, which may be described as the “master” box. 
     Similarly, FIGS. 14A (left end) and  14 B (plan view) illustrate the use of boxes selected from those of FIGS. 13A and 13B to form a structure under the surface  306  of the water. Two “C” boxes with inner partitions  98  are positioned end-to-end, and are overlapped by box “D”. Two “E” boxes are similarly placed, with their midpoints overlapping the junctions of the “C” boxes. Pairs of boxes can be interconnected by mechanical fasteners  99 . 
     FIG. 15 is a top view of an improved version of the box  90  of FIGS. 10-12, with a partition wall  102  dividing the box  101  into halves  101 A and  101 B. The box has the general shape of a parallelepiped, with certain preferred ratios of dimensions which are discussed above. Vertical, horizontal and longitudinal sections of conduit are cast into the walls to form holes  96  in the corners and midpoints of the walls. These formed pipes can be used for reinforcement (shown as  97 ), lifter and stacking attachment points and post tension cables or conduits for wires or fluids when used as building modules. Slab tops  92  (not shown here, but similar to those of FIGS.  11 / 12 ) can be used to seal the boxes. Alternatively, such boxes could be cast in two halves, either top and bottom or front and back portions. Pressurized fluid (water and/or air) could support an internal expendable lightweight form to support the wet concrete being cast atop the cured bottom half to create a unitized watertight structure. Flood and drain holes  108  pass through the sides of box half  101 A for flooding or draining, as discussed below, and are protected by internal grates  130 . 
     FIGS. 16 and 17 are side and end views of an improved box  101 , similar to box  101  of FIG. 15, illustrating devices for flooding and blowing the box when in the water, and for fastening such boxes together to form a structure. The boxes are completely enclosed, including a solid top or top half bolted and sealed with gaskets, elastomeric sealants or other suitable sealing means. Cables  106  are connected to the left side of box  101  through holes  118  in the corners and tensioned to compress a line of boxes together, and are also connected to the adjacent box in an array thereof. Resilient cushioning materials such as used tires  104  are preferably suspended from cables  106  between the boxes to minimize impact damage where desired. Such cushioning materials should be placed at each corner between adjacent boxes. 
     FIG. 17 is an end view illustrating the placement of such tires, using holes  118  in the corners of the box. Flood/drain holes  108  (shown as one method for  101 A) at the bottoms of the sides of the box half  101 A are penetrated by knocking out a thinner casting of concrete should the box need to be flooded and sunk or later blown and surfaced. These holes are protected by inner grates  130  to keep out gravel, etc. Valve assembly  112  with an expandable washer which seals inside against air pressure, an example of which is shown inserted as  112 A, is held in place in blow and vent hole  109 , and sealed by a flexible “bayonet” anchor washer  113 . An expandable and threaded quick connect blow fitting (shown in FIG. 30) is an alternative. Holes  115  penetrate the reinforced section adjacent to partition wall  102 , and can be unplugged and fitted with pipe snap-in connections  116 . To flood the box, hose  117  can be attached to the discharge of a pump or inserted into the sea and used as a siphon with hole  108  open, or alternatively inserted in valve  112 A open as a vent. To deballast water, this is used if the flood/drain holes  108  are intact and are covered by accreted sand. Also, these holes  115  can be interconnected to equalize pressures between the two sections of the boxes to float level. One end only could be deballasted to raise that end and break the bottom suction forces to surface the box. Alternative flood/drain holes  119  can be included in the bottoms of the boxes, with external plugs which could be uncovered and removed to permit deballasting. The box can be made to float unevenly if needed by partially flooding the portion at the end to be deeper. 
     FIGS. 18 to  20  illustrate a method of floating single compartment boxes into position and sinking them in place for installation. FIG. 18 is a side view of a box  101  floating near the surface of a body of water  120 . Box  101  can be attached to a similar box via cables  106  attached at the corners or passing through holes  118  at the corners (only partially shown for clarity). High pressure blow/vent valves  126  (similar to valve  112  in FIG. 16) are fitted to the top of box  101 . As an addition, a septum with an air pipe or simply an air pipe  122  with valve  124  can be used to break suction, and air can be ejected through the bottom at  128 . Grated flood/drain check valves  131  are fitted with rubber flapper covers  132  which close after the box has sunk to the bottom to prevent sand entry, but open when air pressure forces water out of the box for deballasting. 
     As shown in FIG. 19, several boxes  101  can be interconnected to form an array, with cables  106  and tires  104  between adjacent boxes. Alternatively, larger cushioning materials  134 , such as an inflatable fender, rope fender or the like, can be employed. In operation, a single box  101  or an array thereof (FIG. 19) is placed in the body of water near the proposed underwater or tidal installation and moved into position. The box or array can be pushed or towed by tugboats, small boats or any other suitable force. Once in position directly above the proposed installation site, the box or boxes are sunk in place by opening vent valves  126 . Hydraulic or electrically operated valves, actuated by suitable signals conveyed by electrical, acoustic or optical (i.e., fiber optics) means, can be opened sequentially for a controlled and coordinated sinking of the boxes. The box or array will normally require some longitudinal restraint or guidance, such as anchors, to ensure that it sinks into the desired spot. Lines tended by anchored boats or divers should suffice for side-to-side alignment of the boxes. Alternatively, anchors and small craft or tugs can be used, as illustrated in FIGS. 46-48. 
     FIG. 20 is a side view of a box  101  which has been sunk in body of water  120  to rest upon the bottom  131 . Rock, gravel, sand and other materials can be added in and around the structure to create great mass inside (if  101  is an open box) and a higher sea bottom around the box or array thereof, as indicated at  133 , and with time and tide, additional sand, silt or other materials may collect around the structure to create an even higher bottom surface, as at  135 . Also shown in FIG. 20 is a pipe or tube  136  extending from top to bottom of box  101 , providing an alternative method of flooding and draining the box. Air can be vented through valve  126  while water is siphoned into or is pumped in through pipe  136  to initiate flooding of the box, until pipe  136  is submerged when air venting through valve  126  will suck water in through pipe  135 . Suction can be applied to substantially drain the box when needed, with air admitted through a hose, or while air under pressure through valve  126  will also do the job. Pipe  136  is permanently installed or can be inserted through unplugged precast holes. 
     FIGS. 21,  22  and  23  illustrate the use of anti-scour plates in conjunction with the boxes of the invention. As described for the L-walls of the invention in U.S. Pat. No. 5,697,736 at columns  5 / 6 , waterfront structures subject to waves, tidal action or storms may require devices to prevent water from “scouring” or eroding the beach material from under the seaward edge of the structure. FIG. 21 is a plan view showing anti-scour plates  140  attached to both sides of box  100  at the lower edges by mechanical means  142  such as hinges, hooks, rings, cables or the like. When both sides of a box incorporated in a waterfront structure are exposed to water, anti-scour plates on both sides may be required, as seen in FIG.  21 . As shown in FIG. 22, when installing box  100 , anti-scour plate  140  can be lowered into a position to contact the beach or underwater bottom surface beside the box. Prior to installation, anti-scour plate(s)  140  can be retained in place against the sides of box  100  by suitable mechanical means such as lockable lashing eyes (shown in FIG.  25 ). As shown in FIG. 23, the anti-scour plates  140  can be raised or lowered into position by any suitable mechanical means, e.g. using cables  146  attached to attachment points  144  and winch  148  (or other hoisting means). Once lowered to contact the beach surface, such anti-scour plates may be covered by deposited sand and gravel or scoured and lowered to a position of stable equilibrium and embed themselves in the beach or underwater bottom surface to prevent water from removing beach material from under the edge of the box. Such anti-scour plates can be formed from precast concrete, corrosion-resistant metals, geotextile materials, polymer composites, or any suitable material which has the required properties of stiffness and durability. The boxes can be shipped with anti-scour plates attached, or the components can be shipped separately. 
     FIGS. 24 and 25 illustrate mechanical attachment means which can be used to fasten such anti-scour plates to the boxes. FIG. 24 is a perspective view of a commercially available “twistlock stacker”  150  used to interconnect containers on container ships. These units include locking plate  158 , attached to body  160 . Handle  154  is used to manually rotate locking plate  158 . To form a hinge, a large bolt  153  can be inserted through eye  155  of one unit (on top  156 ) and through the eye of a similar unit. The hinge is suitable for one-time uses, as in securing anti-scour plates to boxes. 
     FIG. 25 is a perspective view of two D-ring lockable lashing eye units  170 , having D-rings  178  attached to D-ring hinge  176 , which can be attached to boxes  100  by divers, or on the ship before offloading, and linked by mechanical means including chains, U-bolts or detachable links  180 , closed by nut  182 , to form a hinged attachment of the anti-scour plates to the boxes. The units can include lock  172 , and the D-rings  178  are attached to plate  174 . Such fittings are commercially available from many marine supply houses. 
     FIGS. 26 to  29  illustrate methods of attaching adjacent boxes  100  and/or  101  together to form arrays. FIG. 26 is a side view of two adjacent boxes  100 , each having a locking plate receptacle  180  cast into the corner of the concrete box and anchored by steel connectors such as reinforcing bars  182 . Such units consist of a hollow metal box with smaller racetrack opening  185  embedded in the concrete to receive locking plate  186  of twist lock inserted through opening  185  and twisted with lashing eye  189 . Chains, cables, turnbuckles or other suitable mechanical connecting means (not shown here, for clarity) can be fastened to locking plate  186  to connect the boxes. These connecting means can be used in lieu of or in addition to tensioned cables  106  (see FIGS. 16,  18 ,  19 ) for interconnecting the boxes. Such connecting means can be connected onboard the ship or barge before offloading, or by divers on the bottom. 
     FIG. 27 is a side view of two boxes  100  held together by a differential screw  190  and cushioned by used tire  104  or the like. Female twist-lock locking plate receptacles  180  which are welded to reinforcing bar and cast into the concrete box (same as in FIG. 26) contain an oval or oblong lip and recessed larger opening underneath. Nuts  188  are included and attached pivotally to locking plate  186  through which differential screw  190  can be threaded through a twist-lock lug  188  to fasten the boxes together. Holes  187  in locking plate  186  provide recesses for a tool to apply torque to the lock. Fittings  192  for a power-driven drill socket are provided to tighten differential screw  190  and produce the desired spacing of the boxes and screw tension. 
     FIG. 28 is a side view of a simpler connecting system in which boxes  100  are fastened together by a turnbuckle  200  connecting recesses  187  in bases  184 . Many standard commercial turnbuckles can be used, with hooks  206  of turnbuckle screws  202  inserted into recesses  187  and tightened by rotating turnbuckle screw  204 . 
     FIG. 29 is a side view of two boxes  100  having recesses  187  in bases  184  installed in each corner, which are to be connected by a strong metal plate  210  (or the like) and two twistlock stackers  212 , shown schematically in perspective as attached to the plate. The boxes are connected simply by positioning them the correct distance apart and inserting and tightening twistlock stackers  212  (shown in detail in FIG. 24) into recesses  187  and locking them therein. 
     FIG. 30 is a sectional view of a quick-connect fitting  220  inserted through a hole  254  in box  100  or  101  (formed by pipe  244  cast in place or placed in hole  254 ) for venting and blowing. A hole  254  is molded or otherwise formed in the wall, top or bottom of box  101 , and is lined with or cast with a polymeric pipe insert  244  which is formed of polyvinyl chloride, another suitable polymer or other suitable material. Grooves  240  in the outer surface of insert  244  will retain part of the wet concrete and bond the insert to the concrete hole if inserted during molding. Grooves  241  on the inner surface of pipe insert  244  can be fitted with elastomeric O-rings  243  to provide a seal between pipe insert  244  and locking fitting  230 . A larger tight O-ring  242  fits in groove  245  to provide a force to squeeze locking arms  234  of the locking fitting  230  inward to allow a fit into pipe insert  244 . Locking fitting  230  is fitted with top flange  232  and flexible locking arms  234 . Additional O-rings  238  are fitted between top flange  232  of locking fitting  230  and the concrete wall of box  101  and pipe insert  244 . Locking fitting  230  is formed so that the upper portion of its inner aperture is threaded ( 256 ) and the lower portion of this aperture has a smaller diameter than the threaded upper portion. This allows unthreaded cylinder  229  to fit through locking fitting  230 . Inner spreader insert  222  has a top hexagonal flange  224  and is externally threaded ( 226 ) to be screwed into threaded aperture  256  of locking fitting  230 . Inner spreader insert  222  has a lower, unthreaded cylinder  229  which contacts the tapered insides of the locking arms  234  of locking fitting  230  when it is screwed in and spreads the locking arms  234  to contact pipe insert  244  with a cam action to lock and compress O-rings  238 . With the quick-connect fitting secured and sealed to box  100  or  101 , an air line with shutoff valve (not shown) can be inserted into hole  228  and locked into groove  259  to form a quick connect coupling to permit air to blow the water ballast out of the box or connect to vent valve to contain air to float the box or release air to permit flooding and sinking. 
     FIG. 54 illustrates a shoreline reinforcement system installed along a shoreline having a sloping beach, a low bluff and sand dune systems shoreward of the bluff. A series of L-members of the present invention (or large T-walls.) ( 2 ) are installed along the base of the low bluff to form a seawall ( 740 ), with footers ( 6 ) being covered by rubble and fill graded down from the dune systems. Splash plates ( 10 ) of the L-members protect against scouring by wave action. Preferably, small rocks under armor stone are used to cover the splash plates to further resist scour (not shown in this figure; see FIG. 4 of U.S. Pat. No. 5,697,736). Several groins ( 742 ) perpendicular to the seawall are formed by inverted T walls ( 50 ), extending down the beach and along the shoreline to protect the areas most vulnerable to erosion. Preferably the inverted T-walls are secured to the seawall, as shown in detail in FIG. 11 of U.S. Pat. No. 5,697,736, by having base sections ( 53 ) of the inverted T-walls inserted under splash plate ( 10 ) of the wall, with the stem ( 52 ) of the T passing through cut ( 60 ) in the splash plate. Additionally, at least one series ( 744 ) of inverted T-walls ( 50 ) is installed parallel to the seawall, further down the beach. This provides a stronger reinforcing structure and has the added beneficial effect of helping to form a “perched beach” or area where sand, pebbles and other desired material can accrete. Concrete reinforcing mats ( 746 ) such as Cable-Concrete or the interconnected concrete tie mats of U.S. Pat. No. 5,697,736 are installed behind the seawall and the row(s) of inverted T-walls parallel thereto to protect the beach from erosion and allow for further accretion of sand, etc.; and below the lowest line of inverted T-walls to protect against scour. Mats  746  comprise rectangular sections of concrete  748  connected together side-by-side by cables  750  or other suitable connecting means. All the concrete components are interconnected by suitable, connecting means or fastening means at their points of contact. 
     The system shown in FIGS. 55 and 56 described in Example 3 of U.S. Pat. No. 5,697,736 was designed, built and installed for reinforcement of the Potomac River bank on residential property at Colonial Beach, Va. Starting at the right (northern, upriver portion) of FIG. 55, a portion of the bank was designed as bevelled and protected by armor stone  756  erosion by the current. The angle of the bevelled portion was selected to help to deflect floating debris; ice and the like. Approximately 200 feet of the bank was reinforced by sections of L-walls ( 2 ) installed to form a sea wall. After entrenching the beach below the bank and positioning the L-walls with their keys ( 8 ) firmly placed and levelled, the upper bank was graded and used to fill over granular fill  752  (rocks, gravel and sand) that have been used to cover footers ( 6 ) of the L-walls. Weep holes ( 14 ) are provided in the L-walls for drainage, and the walls were joined end-to-end by bolts or other suitable connecting means. The splash plates ( 10 ) of the L-walls were covered first with core stone ( 754 ) over a layer of geotextile ( 29 ), then with armor stone ( 756 ) to protect against storm and ice damage. The southern/downstream (left) end of the wall was protected by armor stone ( 756 ). 
     A series of five groins ( 742 ) was installed, extending approximately 20 feet from the wall and approximately perpendicular thereto. The groins were formed of inverted T-walls approximately 3 feet high by 3 feet wide, and placed so as to nourish the present beach with sediment. A pier groin ( 750 ) also extends from the wall in a perpendicular direction, for about 300 feet. The pier groin was constructed of inverted “Double-T” units. This system was designed to protect the presently eroding river bank, encourage accretion on the present beach and enhance recreational use of the area. 
     FIGS. 31 to  33  illustrate the use of such concrete boxes to construct a waterfront boathouse. Plan view FIG. 32 (without roof deck  314  for clarity) shows three or more concrete boxes  103  of suitable size and proportions assembled open side up, optionally fitted with concrete or wooden tops (e.g., as shown in FIG. 12) upon the bottom  304  of a shallow harbor or other body of water  306  in a U-shaped configuration forming a mooring area  308  to shelter a boat  310 . The upper surfaces of the boxes  103  can be fitted with standard mooring fixtures and the like (not shown here), and allow passengers to easily embark and debark on or from the boat. Boats may be moored on the outer sides of the boathouse as well, if desired. As shown in end view FIG. 31, boxes  103  are higher than the depth of water  306 , but for deeper water or locations where minor tides occur, boxes  103  can be stacked two or more layers deep to provide an upper surface which will lie above the highest normal water level. Holes  302  are provided in the closed bottoms and/or tops of boxes  103 , or alternatively outside of the boxes, to accommodate pilings  312 , which are driven into bottom  304  to retain boxes  103  in place. The boxes can also be interconnected by mechanical means, as discussed above. 
     The pilings are hollow tubes of metal or plastic pipe, which are filled with concrete when all boxes and pilings are in place to provide permanent structural strength. Since the main strength is provided by the concrete thus cast, the material for the pipes is not critical, but they are preferably made of durable plastic materials such as PVC so that they will not corrode. The boathouse structure here is emplaced with the closed end toward the shore (with normal walkways or the like provided for access, but not shown here) and the open end toward the water for boat access. The closed end of the boathouse is shown in FIG.  31 . 
     Optionally, a roofdeck  314  can be provided, comprising a solid deck  316  perched atop pilings  312  and secured in place mechanically. Deck  316  can also be of precast concrete of suitable thickness such as precast sections spanning the distance between pilings  312  and any necessary supports, wood, recycled plastic “lumber” or any suitable building material. Preferably roofdeck  314  includes an open railing  318  suspended from posts  319  for safety, and is provided with access by stairs or ladders (not shown) for use by the owners. Movable or fixed side curtains or other closures such as fixed walls (not shown) can be provided for privacy and protection of boats using the structure. 
     Since such a structure with completely solid sides underwater could be vulnerable to scouring and forces exerted by local currents, as shown in FIG. 33, arched passages  320  and/or pipes or culverts  321  are cast or cut into the sides of boxes  103 , extending approximately as high as the expected water level  306 , to allow any currents to flow through as indicated by arrows in FIGS. 31 and 32. These boxes are preferably cast with a solid surface extending along arch  320  to provide a bottom of the box to hold sand which can be added for ballast. A flat bottom can also be included to spread the weight of the structure over a larger area, and the structure can also be mechanically attached to piles  312  for support to prevent settling. 
     FIGS. 34 and 35 are open end and plan views of a floating boathouse  400  employing enclosed boxes  103  of the invention. Boxes  103  are again assembled to form a U-shaped structure to accommodate a boat  310  therein. The boxes are interconnected by suitable cables or connectors as shown in FIGS. 26,  27  and  28 . Boxes  103  float in water  306  adjacent to shoreline  402 . The boxes can be completely precast or enclosed by adding precast concrete covers as described in FIGS.  11 / 12  or decks of wood, recycled plastic lumber or the like. To help the boxes to float, they can be sealed to retain air, can be compartmented as shown in FIG.  15  and/or filled with foam, ping-pong balls, styrofoam packing materials or other buoyant materials. Intermodal-sized boxes which measure eight feet square by forty feet long can conveniently be used. Boathouse walls  404  are erected upon the upper decks of boxes  103  to form a boathouse structure thereon. Walls  404  are preferably strong weight-bearing solid walls (using suitable construction materials discussed above) to support an optional deck  314  as described above, but can be cut out to form windows, doors, etc. Roof deck  316  supports rails  318  supported by posts  319 . Beams  406  extend from the inner upper edges of boxes  103  to the lower surface of roof deck  316  to increase strength and rigidity. The top decks of boxes  103  can be fitted with appropriate mooring fixtures for boat  310  (not shown here), allowing mooring both inside and outside the walls. The boathouse itself can be secured to bottom  304  by standard mooring systems such as a four point moor, chains  410  to clump anchor  412 , or screw anchors  413 . The boathouse can also be retained in place by a number of piles  105  passing through rings or brackets  107  which are attached to the sides of boxes  103 . Ramp  408  or other suitable means can be used to provide access from the deck of box  103  to boat  310 . Similarly, optional pier or walkway  410  connects the floating boathouse to land  402 . Two or more rigid spacing bars  315  are provided between the arrays of boxes and mechanically attached at  317  to keep them in alignment. This boathouse design can provide a relocatable, permanent or temporary facility for pilots, marine patrols, military forces, Coast Guard, and the like. 
     FIGS. 36 and 37 (plan and side views) illustrate a standard fixed boathouse design  420  with a series of concrete boxes  103  added around the supporting piles  311  to protect them from ice and storms by adding mass to the structure and deflecting floating objects. The piles can be any conventional type of wood, metal or concrete, or pipe filled with concrete as discussed in FIGS. 31-33. The concrete boxes which are placed about the piles are precast concrete boxes as described above, which can have either closed or perforated sides, and are approximately square in cross-section, preferably being approximately cubical. The piles are inserted through holes placed in the bottoms (and tops, if present) of the boxes, which are stacked in the positions where the piles are to be driven. Once the piles are driven and the boxes filled with water and sand or gravel, the assemblies for a support for the boathouse (or other structure) that is almost impervious to floating ice or other debris, waves or currents. The boxes are stacked and interconnected by methods discussed above. Such precast concrete structures extending from the bottom to the waterline or higher can be employed to protect various types of waterfront structures, such as decks, mills, dam or power plant components and the like. Lifts  423  can be provided to lift boats out of the water. 
     FIGS. 38 to  40  illustrate a precast concrete “bridge box”  450  which is a long, flat parallelepiped in form, including a hemispherical, round, rectangular or oval cutout portion  452  in both of the longer sides. The box can be closed on all sides except where cut out, or can be open on the bottom below cutout  452 . Preferably the box is cast with a solid bottom along cutout portion  452 , to retain sand which may be added via suitable inlets for ballast. Alternatively, pipes  453  of appropriate number and size can be cast into an otherwise completely enclosed bridge box. FIG. 38 is a side view of a single bridge box  450 , while FIG. 39 is a top view of a bridge  454  assembled from three boxes  450  placed side by side to form a roadbed or path, cutouts  452  coinciding to form a culvert  455  for a stream or other running water to pass under. 
     FIG. 40 is an end view of the bridge  454  of FIG. 39, showing a water flow  456  through the culvert. Preferably concrete anti-scour plates  458  are fitted by hinges  457  on both sides of boxes  450  to protect the lower edges where water flows through the culvert. Additionally, large or small pipes  459  and  460  cast into the boxes as conduits provide ready-made and protected means for installing utility lines. Such bridges or structures can be incorporated into shoreline reinforcement systems constructed in accordance with the invention. They can also be used to construct structures requiring bases which will accommodate water flow, such as the boathouse illustrated in FIGS. 31-33. This bridge box structure and method could provide for much cheaper and faster construction of bridges, addition of traffic lanes, or replacement of old bridges over small streams and rivers. They could also be post tensioned over a wider stream or marsh. This design could also be used as a box penetration for storm water to pass from beachfront roads through “boardwalk” boxes and berm boxes to allow storm water to flow to the sea. 
     FIGS. 41 and 42 illustrate a shoreline reinforcement system constructed primarily of precast concrete boxes in accordance with the invention. In form and effect, this system resembles the systems disclosed in U.S. Pat. No. 5,697,736 in columns  11 / 12  and FIGS.  18 / 19 . FIG. 41, the plan view, shows an array of boxes of various sizes assembled along the shoreline to form a seawall and a “backbone” structure for a berm or sand dune seaward of the seawall. These boxes, in suitable sizes and proportions and numbered  501 ,  502  and  503 , will generally be installed by heavy equipment such as cranes or tracked excavators, either from seaward or shoreward, and are filled with sand to provide permanent ballast. They can then be topped with permanent precast concrete covers if desired to form a walkway atop the seawall and prevent scour of the fill inside the box. These boxes can be described as “boardwalk boxes”  501  and are described in detail and illustrated in FIGS. 10-12. The boxes can take the form of rectangular parallepipeds, typically about eight to twelve feet wide by twenty to forty feet long by eight feet high, or can be nearly cubical units half that long. The large boxes  501  shown are segmented (with partitions  102 ) and can be about eight feet square by forty feet long. Using boxes in at least two lengths facilitates their installation in lengths suitable for the construction site and local conditions. Also, as described above, it is convenient for shipping to use intermodal units having lengths of ten, twenty or forty feet. 
     Extending laterally down the beach from the seawall are at least two arrays of “berm boxes”  502 , which can be about four feet high by eight feet wide by twenty feet long, to provide berm groins and closed berm cells  504  much like those employed in the systems in the patent cited. Smaller box groins  503  form open groin cells  505 . These may be open boxes which are filled with sand and then fitted with tops, or if local tidal conditions permit, can be floatable boxes which are floated into position and then sunk in place, as described above. Another lateral row of berm boxes  502  is installed perpendicular to the berm groins and approximately parallel to the seawall, filled with sand and left open or covered. The beach spaces between the berm groins and lateral rows of boxes are partially filled with sand and preferably covered with filter cloth and articulated concrete mats as disclosed in the patent cited, in columns  10 / 11  and FIGS.  16 / 17 , then covered with more sand. 
     Alternatively, the spaces can simply be partially filled with gravel, rip-rap and/or sand, and local winds, tides and waves allowed to deposit additional sand, etc. with time. The result will be a stable structure that prevents erosion of the shoreline and actually tends to build up sand and gravel to form additional beach under most conditions. Storm protection is also provided for the boardwalk (or seawall) boxes and the landward buildings and other structures. 
     Additional smaller groins  503  can be added to seaward of the lower lateral row of boxes described above. Such groins  503  can be formed of arrays of at least one “beach box”  503  (which can be about four feet wide by four feet or 2′ 8″ high and ten or twenty feet long) at the right and left sides, as described above for the berm boxes, and filled with sand or gravel for ballast. Such boxes are preferably set from the land, or if intended to extend into the sea, floated into position and sunk in place for installation. In addition, or as an alternative, T-walls  506  and bevelled T-walls  507  can be used as shown in the center and described in the patent cited, in column  7  and FIGS. 8,  9  and  18 . Such T-walls could be used for the entire pier-groins as disclosed in the patent cited, or simply to provide the seaward components of this system (in which case the bevelled ends of the outward T-walls minimize potential damage to boats and the like which approach closely). In general, with no beach existing, it will be easier to install beach boxes where they can be floated into position, so they are preferred for most components of the systems of the present invention. With an established beach, installation from landward is preferred. The double T or “pi” units of FIG. 3 can also be used as components of such shoreline systems, arranged parallel and/or perpendicular to the shoreline. 
     FIG. 42 shows the system of FIG. 41 in side view, the entire structure lying above mean high water, and the level of sand expected to build up after storms and after renourishing by normal tidal action or by artificial methods. This system can be installed before renourishing an eroded beach to retain a large percentage of the new sand, which might otherwise be washed out to sea during a storm. Even if some of the sacrificial sand is lost, these massive interconnected boxes and other structures are not easily moved by storm waves. However, if necessary, the boxes can be disconnected and relocated, using suitable heavy equipment. 
     FIGS. 43 to  45  illustrate a novel vessel  570  and method for transporting and installing precast concrete boxes of the invention to locations for installation to form shoreline structures, breakwaters and the like. Plan view FIG.  43  and side view FIG. 44 show a vessel  570  comprising two portions, bow  558  and stern  552 , fastened to midsection  562 . Stern portion  552  comprises the conventional propulsion system (not shown), at least one propeller  554  and pilot house  556  with appropriate controls. “Thruster” type propulsion  559  can also be provided to improve maneuvering. Bow  558  comprises storage spaces for supplies, at least one anchor (not shown) and a crane unit  560 . Both sections have flat vertical surfaces comprising primarily watertight bulkheads with a minimum of openings which can be secured to permit them to float independently. Bow  558  and stern  552  can be fastened together as shown in side view FIG. 45 to form vessel  550  and secured by appropriate mechanical means such as larger twistlock stackers (as shown in FIG.  28 ), turnbuckle locks, bolts, cam locks and the like. Thus secured, vessel  550  can travel under its own power to a port where a stacked and securely interconnected floating array of precast concrete boxes of the invention can be attached between the bow and stern sections for transportation. 
     As shown in FIG. 44, a large group of such boxes  101  can be stacked and grouped together to form a box module  562 , which is fastened together under longitudinal and lateral tension by a tensioning system comprising, e.g., corners  564  and  566  and cables  568 . Similar locking connections on the corner plates permit the array of boxes to be secured to the bow and stern sections of the vessel. Once assembled, box module  562  is moved from an onshore assembly site (e.g. on a pier, wharf or ramp) by large crane or other suitable means into the harbor waters and floated into deeper water alongside a pier or within the harbor where the vessel may freely enter. Such a module can be maneuvered around such restricted waters using mini-tugs (e.g., converted military landing craft) or other suitable small craft and suitable attachment points which are provided on the outside surfaces of the module (not shown here). 
     With the module held in place by such tugs, anchored or moored to buoys, vessel  550  can be brought alongside, bow section  558  detached from stern section  552  and stern section maneuvered against the rear surface of the module  562 , using propeller  554 , thruster propulsion  559  or tug assistance if necessary. Contemporaneously, tugs or other craft hold bow section  558  in position until stern section  552  is attached to module  562 . The vessel&#39;s anchor can be used to anchor bow section  558  during this period if desired, provided that an auxiliary power source is provided to power the anchor windlass. Then bow section  558  is maneuvered into position against the front surface of module  562  by tugs and secured in place. The same systems used to fasten the bow and stern sections of the vessel together can be used to attach the bow and stern sections to the array  562  of boxes. The result is a “stretched” vessel  570  (shown in FIGS. 43 and 44 assembled, FIG. 46 in disassembled state) which can travel under its own power to the location where the boxes are to be disassembled and/or installed. 
     In addition to transporting and unloading such floating arrays of concrete boxes as described above, the vessel of the invention can be used to carry a variety of other floating objects or arrays of objects, provided they are sufficiently buoyant, have appropriate proportions and can be fitted with attachment devices to attach them securely to the two hull sections of the vessel. Various types of containers and tanks, floating bridges, pontoons, caissons and other floating construction components can be incorporated in the vessel and transported. This could be of particular value when transporting and installing components to form structures in areas of military landings. Furthermore, such a vessel could be constructed to have the appropriate size, proportions and attachment fittings to transport floating drydocks, whether commercial or military. Since floating drydocks have high freeboard and limited stability at sea, transporting them as the midship section of such a vessel could provide a faster and safer method of overseas transport for these valuable ship repair vessels. 
     FIG. 45 is a side view showing the vessel  550  with bow section  558  and stern section  552  again connected together, box module  562  having been removed by reversing the sequence of steps described above. Thrusters or mini-tugs (not shown here) can be carried on the forward deck and/or in a forward hold and offloaded using crane  560  to facilitate this process. In FIG. 45, a portion of the module tensioning system has been loosened and crane  560  is lifting the first box  101  to be offloaded. Depending upon the depth of water near shore and the positions where the boxes are to be installed, the vessel and crane may be able to deposit the boxes in the water directly above or near the installation point, or near the installation point ashore. Alternatively, the boxes can be placed into the water near shore and maneuvered into installation position by mini-tugs or other suitable craft. 
     FIGS. 46 to  48  illustrate another method of transporting and installing arrays of precast boxes of the invention. FIG. 46 is a side view of a barge  600  or similar vessel floating in water  602  over bottom  610  where a breakwater is to be installed. Vessel  600  can be self-propelled, in which case propellor  620  and associated propulsion systems are provided. Precast concrete boxes  604  are connected by stainless steel cables  606  (or other suitable mechanical means) and arranged on deck  612  in position to be unloaded as an array via ramp  608 . The boxes can be the special perforated and slotted “breakwater boxes” disclosed in U.S. Pat. No. 5,697,736 and illustrated herein in FIG. 4 (having thin concrete knockouts or plugs), but can also be open boxes as in FIGS. 10 to  12  or closed boxes fixed with flood/drain and blow/vent valves as illustrated in FIGS.  16 / 17 . Ramp  608  can be held in position during operations by using suitable mechanical restraints such as cables or hydraulic rams, as well as floats. 
     The array of boxes can be unloaded from the barge by dropping a heavy anchor  614  which is attached to the array by extended cable  607 , then backing the barge (by self-propulsion or tug, not shown here) to exert tension on cable  607 , as illustrated in FIG.  47 . Barge  600  will require a smooth, level deck upon which the array of boxes can be arranged, and providing rollers or lubrication before the boxes are loaded and connected would be helpful. FIG. 47 illustrates the array of boxes  604  floating on the surface  602  and interconnected by cable  606  (not seen here), with the boxes pulled closely together. One end of cable  607  is still held by anchor  614 , but the array of boxes has been moved closer to that anchor by winches or boats to bring it near the point where the breakwater is to be installed. At the other end of the array, cable  606  passes through block  618  on anchor  615 , which was dropped from the barge deck after the last box slid down ramp  608 . Clamps or other mechanical restraints  616  and  617  position the array of boxes at preplanned portions of cables  606  and  607  after the desired amount of tension on cable  606  and the desired position of the array is attained. This is accomplished by applying force to the barge end of cable  606  via a winch (not shown) or other appropriate device. 
     When the array is in optimum position for installation as determined by navigational or global positioning system fixes, all boxes are sunk sequentially or simultaneously by remote control or manual means, and allowed to settle into their installed positions to form a submerged breakwater or reef  622  as shown in FIG.  48 . Cable  606  can then be simply cut from the barge deck, or if desired, a diver can be employed to secure cable  606  to block  618  on anchor  615  and the excess cut, to provide extra security for the breakwater. As discussed in the patent cited, at columns  8 / 9 , such breakwaters can be very beneficial in reducing or eliminating the presence of swells in harbors which are at least partially exposed to open water. As an alternative, the interconnected boxes can be left floating to mitigate passing wave energy. 
     FIGS. 49 and 50 illustrate how the precast, intermodal concrete boxes can be used to construct buildings for use either above or below ground or water. Dwelling structure  650  includes first floor  654  and second floor  652 , all constructed of precast concrete boxes of various standard sizes and proportions, being interconnected and stacked to form the two (or more) stories. The concrete boxes are amenable to intermodal transportation as well as lifting and placement on the ground (or actually in water, if the bottom units are waterproof) or stacking, as illustrated in FIG.  49 . Doors, windows, open walls, conduits for utilities, and the like (not shown here) can easily be included for use in these standardized boxes and/or cut during installation/assembly. The walls of the precast boxes in effect become interior and exterior walls, floors and ceilings of the various rooms or spaces contained within the structure. 
     Because the concrete is stong, resistant to liquids and vermin, it can be used in wet areas, acidic soils, underground, on water, under water and in other challenging environments. It is ideal for constructing strong, relocatable structures, such as for military or security areas. Such precast boxes can be ideal for constructing bunkers, fallout shelters, underground or underwater storage facilities or earth-sheltered homes. FIGS. 49 and 50 illustrate the employment of precast concrete of various sizes and proportions suitable for forming various typical rooms of a combined dwelling/office structure. For example, large unfinished modules  658  can be used for garages or the like, and smaller modules  655  and  656  can be used for bathrooms and bedrooms. 
     Some applications of precast concrete boxes of the invention for shellfish habitat are illustrated in FIG.  51 . In many areas, the cultivation of shellfish such as oysters and mussels has been adversely affected by pollution and silting of bottoms of bays and other bodies of water, which may be exacerbated by harvesting techniques which disturb bottom sediments. To permit the cultivation of shellfish above the bottom in such areas and facilitate harvesting without aggravating such problems, FIG. 51 provides a precast concrete box  700  with enclosed sides containing holes  702  and/or slots  704 . As illustrated in FIG. 4 above, these openings can be at least partially filled with breakable, thin concrete sections to provide knockout areas to facilitate the sinking of the boxes. The openings in the box permit its use as shelter by small fish, crabs, crustaceans and shellfish. Although the box could be raised by filling it with ping-pong balls, styrofoam particles, inflatable balloons or the like, because of its weight this embodiment is more suitable for use as a permanent seed bed to remain on the bottom. 
     The boxes are provided with removable concrete tops  710  which can be held in place with pins  708  passing through holes  706  in both covers and the corners of the boxes. Shellfish are to be cultivated on the covers of the boxes when sunk into place, thus elevating the shellfish at least the height of the box (perhaps 4 to 8 feet) above the bottom where they are removed from silt and pollutants and exposed to currents carrying more nutrients and oxygen. The boxes preferably have dimensions and proportions which permit intermodal transport and the covers are provided with various types of projections or roughened surfaces to promote adhesion by shellfish spat. This working surface of the covers is turned inward for convenience in transport, then is reversed and secured in place before sinking and installation of the boxes. In FIG. 51, cover  710  is covered with at least one layer of projections  712  (here, three layers) having the form of rectangular parallepipeds, which can be laid down horizontally in criss-cross patterns as shown. In addition to producing boxes and covers of concrete comprising crushed bivalve shells, preferably oyster shells, the projections  712  can be cast or otherwise produced of similar materials. The objective is to provide rough, porous surfaces which are hospitable to shellfish spat, with projections which are spaced appropriately to foster rapid and productive growth of the shellfish to harvestable size. As an alternative or addition to such projections, the covers can be cast to contain large fragments of broken bivalve shells, as shown in FIG. 52 as  717  on concrete cover  710 . This in itself could provide an ideal oyster bed, but oyster shells and comparable materials are in short supply and must be conserved. Also shown in FIG. 52 are rectangular projections  714  which are cast or attached perpendicular to cover  710 . 
     FIGS. 53 and 53A illustrate another type of shellfish habitat, with FIG. 53 schematically illustrating a meshwork container  701  with attachment points  726  at the upper corners for attaching bridle cables  728  and hoisting cable  730 . Pins  722  are fitted to the lower corners so that the container can be mounted atop a precast concrete box such as box  700  of FIG. 51, or any suitable container or platform which will elevate the habitat to the proper level above the bottom. Any suitable mesh or openwork material  733  can be used to construct containers  701  about a suitable framework including rigid components  732 , including expanded metal, heavy wire mesh and the like. The vertical sides of the container should be mesh as shown, but the bottom can be solid ( 725 ) and/or mesh ( 723 ). For durability, meshwork of stainless steel or synthetic polymeric materials may be preferred. Container  701  is to be filled with suitable objects for the adherence of shellfish spat, such as used tires  724 , optionally filled with broken shells, stainless steel wire mesh structures, plastic pipe reinforced with steel, fragments of concrete, and the like, any of which can contain bivalve shells or mature oysters. 
     Two ways of providing inner mesh structures are to install vertical sections of mesh  736  extending from a narrow end of the container (where they attach to frames  732  and/or side mesh  733 ) to at least the center, where they can be attached to wire or rod supports  727 . Such vertical mesh sections could extend from one end of the container to the other. In addition, or alternatively, horizontal layers of mesh  734  can be attached to a narrow end of the container, extending parallel to the bottom at least to the center of the container, where they can be attached to wire or rod supports  729 . Such horizontal layers of mesh can also extend the entire length of the container. 
     A precast concrete top  710 , much like that shown in FIG. 52, is provided. Various types of projections, including those shown in FIGS. 51 and 52, can be used. FIG. 53A illustrates projections  716  and  718 , which are cylindrical and conical, respectively. Conical projections are preferred, as they are easier to remove from the molds used to cast the assembly. Additional components can be mounted on these projections, such as used tires  720 , optionally filled with bivalve shells, stainless steel wire mesh structures, etc. 
     Since container  701  is much lighter than a concrete box, even when filled with structures for shellfish culture, hoisting and bridle cables  730  and  728  can be used to lift the entire container, cover and all, or alternatively, similar cables can be connected to lift cover  710  independently. Also, if the container  701  is mounted upon a solid concrete box such as illustrated in FIG. 15 having apparatus for introducing air to expel the water, the box itself can be blown and raised to the surface, carrying the container on top. Once either component (the container or cover) is hoisted clear of the water, the contents can be hosed off to remove any silt or sand and the assembly shaken or vibrated over a vessel&#39;s deck or hold to dislodge oysters or other shellfish (e.g., mussels) for harvest. 
     Various changes and modifications to the presently preferred embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. Therefore, the appended claims are intended to cover such changes and modifications, and are the sole limits on the scope of the invention.