FIELD OF THE IN VENTION

This invention relates to earth or fill retaining systems. More particularly, although not exclusively it discloses improvements in levee systems for seawalls, bulkheads, retaining walls and like structures.

BACKGROUND TO THE INVENTION

It is well known to drive prefabricated sheet piles into the ground in interlocking fashion to provide a retaining wall behind which loose fill such as soil or sand is disposed. In order to stabilise and reinforce this fill and to prevent erosion and excessive outward load on the piles it is also known to install horizontal spaced apart grids or mesh which extend back into the fill. This diffuses the outward forces that would otherwise act against the back of the piles by causing the fill to "stack vertically" as opposed to stacking at its natural shallower angle of repose. The outward force imposed against the piles is thus substantially reduced. Such grids or meshes are commonly referred to in the industry as "Geogrids". In addition it has been determined that further benefits to the wall structure can be obtained by connecting the Geogrids directly to the back sides of the piles whereby said piles are "tied back" into the fill.

SUMMARY OF THE INVENTION

Accordingly an earth retention levee system is disclosed which is constructed from spaced apart parallel walls of interlocking sheet piles, said sheet pile having outside faces and inside faces formed with spines along a longitudinal extent thereof, said spines being connected to adjacent edges of Geogrids linking said parallel walls and adapted to stabilise fill disposed therebetween.

Preferably the spines are formed as a continuous flanges extending out from said inside faces with enlarged or bulbous outer edges. It is further preferred that said sheet pile is in the form of a box section which on installation interlocks with another like pile to create a closed wall structure that can be infilled with concrete for increased strength.

It is further preferred that said sheet pile is fonned from a composite material comprising a fibre reinforced polymer.

It is further preferred that said composite material includes reinforcement with biaxial E-glass fabrics, continuous strand glass mat, and aligned unidirectional rovings.

BRIEF DESCRIPTION OF THE DRAWINGS

One currently prefen-ed embodiment of the invention will now be described with reference to the attached drawings in which: - figure 1 shows the angled placement of the walls of the Earth Retention

Levee System according to the invention, figure 2 shows a perspecti ve view of the sheet pile used to construct the walls of figure 1, figure 3 shows a schematic perspective view of the walls with the geogrid mesh and fill in place, figure 4 is schematic perspective view of the inside face of one of the walls showing the preferred method of attaching the geogrid mesh DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to figure 1 the Earth Retention Levee System may be constructed in accordance with the invention using two parallel walls 1 , 2 constructed from sheet piles. They are driven into the ground 3 at a predetermined angle or batter inward toward each other and to a specified depth of for example 600 mm.

Preferably but not essentially the inward slope may be of the order of 5 degrees from the vertical. Each sheet pile as shown in figure 2 is preferably of a box section with inside and outside faces 4, 5 and four lateral flanges 6, 7, 8 and 9. A ridge 10 (hereinafter referred to as a gridspine) runs down the inside face 4. The gridspine with this embodiment is offset to one side of the sheet pile and

preferably aligns with an internal web 1 1 for increased strength. The gridspine is also preferably formed with a broadened outer edge 12. The lateral flanges are preferably angled inwardly at the outer ends and are formed into female and male interlocking clutches 14 and 15 on the right and left sides of the pile sheet respectively as shown. The slots 16 defined within the curved arms of the females clutches are shaped and sized in cross-section for a reasonably close tolerance sliding fit over the enlarged splayed edges 18 of the male clutch whereby the pile is adapted during installation to slidably interlock with an adjacent identical pile to form the solid wall structures 1 , 2 of closed box sections. By virtue of the aforementioned inward angle of the flange ends the interlocking clutches are set into the wall structure to protect them from damage and also provide a protrusion free surface.

Typically the walls 1 , 2 would run adjacent the course of a river or other low lying area subject to erosion. As shown in figure 3 they are connected to each other at their bases and at locations above by reinforcement extending between the piles. This reinforcement preferably comprises the "Geogrid" reinforcement material referred to earlier. The Geogrids 20 are built up in vertically spaced horizontal runs between the walls which are progressively packed in with soil 21 or other suitable fill material. As shown in figure 4 the points of connection between the Geogrids and the inside faces of the sheet piles are preferably by means of a composite fibre reinforced polymer rod 22. More specifically, this rod is preferably made of a fibre composite with substantially corrosion resistant vinyl ester resin and E-glass fibre reinforcement. This composite rod allows for a strong corrosion resistant mechanical connection between the sheet pile and the Geogrid. Based on grid placement requirements the gridspine 10 is drilled and the composite rod is inserted through the holes and Grogrid which is then lapped over the rod and preferably fixed with bodkin connectors. This gives the Geogrid a strong positive longitudinal connection to the sheet pile.

After infilling and compacting the fill between the parallel walls 1, 2 as shown in figure 3 the vertically spaced runs of Geogrid reinforcement 20 serve to spread the soil load acting on the sheet piles by causing the soil to stack vertically as opposed to stacking at its natural angle of repose. This increases global stability, allows the piles to be constructed from a lighter material while reducing the footprint on waterbody easements. Preferably the infilling occurs progressively from the bottom up with the installation of the reinforcing grids. In accordance with the currently preferred embodiment of the invention the bottom

reinforcement grid is secured at the bottom edge of the sheet pile wall and then attached to the other parallel sheet pile wall directly opposite. The fill material 21 is then impacted to a predetermined height above the reinforcement before a subsequent higher vertically spaced horizontal run is attached between the walls. This procedure continues until the required height of infill between the walls is reached.

The piles are installed typically, but not exclusively, by driving them into soil or fill with appropriate pile drivers and the box sections can be subsequently infilled with concrete or other material for added strength. Preferably, although not essentially, a sheet pile in accordance with this invention may be manufactured by a known process called Pultrusion. This creates fibre reinforced polymer profiles of extraordinary strength and resilience. The reinforcement material is drawn through a liquid thermosetting resin bath. The wet fibrous laminate is then pulled through a heated steel die where precise temperature control cures the material into the profile required. The necessary strength, colour and other characteristics can be designed into the profile by changes in the resin mixture and reinforcement materials.

It will thus be appreciated that this invention at least in the form of the

embodiment disclosed provides a novel and improved form of earth retention levee system for retaining walls, sea walls and like structures. Clearly however the example described is only the currently preferred embodiment of the invention and a wide variety of modifications may be made which would be apparent to a person skilled in the art. For example the shape, configuration and dimensions of the sheet pile, the material of which it is constructed and its method of manufacture may change according to application and design preference.