Technical Field

The present invention relates to a mechanical connector for connecting soil reinforcing layers known as geogrids to retaining walls and to other geogrids. Geogrids comprise a layer of e.g. polymeric material provided with regular apertures.

Background Art

The use of geogrids to reinforce soil structures is known. One common use of geogrids is in reinforcing the soil or other material immediately behind a retaining wall. The geogrid comprises a flexible layer of usually polymeric material having regularly-spaced apertures. One type of geogrid is formed by punching slits or apertures in a sheet of polymeric material which is then heated and drawn to form the grid. Uniaxial punched and drawn geogrid is stretched in one direction only and comprises a number of transverse bars interconnected by elongated high tensile ribs, with elongate, elliptical apertures between the ribs. Biaxial punched and drawn geogrid is stretched in two directions and has the appearance of a net or mesh with generally square or rectangular apertures.

When used to reinforce and stabilise soil behind a retaining wall, the geogrid is mechanically secured to the retaining wall and extends horizontally into the material behind the wall for a set distance. Typically, several geogrids may be embedded at vertically-spaced intervals. The retaining wall may be a segmental block retaining wall and the geogrid can be secured to the wall in between blocks. A connector to connect uniaxial geogrid to a segmental block retaining wall is disclosed in WO2007/128566. Alternatively, the retaining wall may be formed from one or more reinforced concrete panels, which may be pre-cast with a short length of geogrid being anchored to the rebars in the panel before the concrete is cast.

Further sections of geogrid may be connected to the geogrid which is secured to the retaining wall. This allows the grid to extend further into the fill material behind the retaining wall to provide an increased stabilisation force on the wall. Various methods of connecting two sections of geogrid together are known. One conventional method of connecting two sections of uniaxial geogrid together involves looping the ribs of one geogrid through the apertures of the other and inserting a rod or "bodkin" through the loops to secure the geogrids together. While acceptable in some situations, this type of connection requires an amount of slack to be taken up before tension is transmitted from one section to the other, which may not be practically possible on site.

The present invention provides an improved connector for connecting a geogrid to a retaining wall and for connecting geogrids together.

Summary of the Invention

In accordance with the invention, a connector is provided which is adapted to be mechanically engaged with a reinforcing layer, the reinforcing layer comprising at least two transverse bars interconnected by longitudinal ribs with apertures between the ribs, the connector comprising a substantially planar base and a plurality of spaced projections extending perpendicularly from the base, the projections being adapted to be inserted into and to project through respective apertures of the reinforcing layer and to engage in use with a transverse bar of the reinforcing layer so that a tension force is transmitted longitudinally from the reinforcing layer to the connector, wherein the projections are resiliently spaced from one another in the transverse direction to allow for variation in the spacing of the apertures of the reinforcing layer.

The reinforcing layer is preferably a geogrid. The invention may be employed with uniaxial or biaxial geogrids.

In the present invention, the longitudinal and transverse directions are preferably the x and y directions respectively. The base of the connector preferably lies in the x-y plane and the projections preferably extend perpendicularly in the z-direction.

In this arrangement, the tension force would be transmitted in the x-direction in use. The force is preferably transmitted from the geogrid to the connector by means of the side or face at a longitudinal end of each projection engaging with the transverse bar in use. In a preferred arrangement, the base comprises a plurality of resiliently-interconnected base flanges with a projection extending perpendicularly from each base flange. The base flanges are preferably interconnected by resilient elements, which may comprise curved spring elements.

The elements are able to compress or expand to adjust the spacing between each projection.

The cross-section of each projection (i.e. in the x-y plane) may be configured to substantially match the shape of the aperture in the reinforcing layer, or part of the aperture shape such as the end region. In a uniaxial geogrid for example, the aperture may be elongate and substantially oval or elliptical at the end, near the transverse bar.

The cross-section of each projection may be elongate in the longitudinal direction and the projections aligned in the transverse direction. The cross-section of each projection may taper in the longitudinal direction from its transverse centre line, and further may be rounded or squared off at each longitudinal end.

The base and projections may be formed separately, but preferably the base and projections are unitary. Any suitable material may be employed to make the connector, including plastics or metal, but preferably the connector is formed from high density polyethylene (HDPE) or polypropylene.

As discussed above, the connector of the present invention may be employed to mechanically connect two reinforcing layers together. The projections are inserted through respective apertures of each reinforcing layer when the layers are in an overlapping relation, the projections engaging in use with a transverse bar of each reinforcing layer so that a tension force is transmitted longitudinally from one reinforcing layer to the other via the connector.

In a preferred arrangement, only the end regions of the reinforcing layers are placed in an overlapping relation, with the layers extending in opposite longitudinal directions. With the connector inserted through the apertures of both layers and on applying tension for the first time, the layers will tend to pull apart relative to one another until the transverse bars contact both sides of each projection. The components will then be secured together. Because there is minimal resilience in the arrangement, there is no slack to take up before a tension force can be transmitted from one layer to another. As described, the side or face at one longitudinal end of each projection preferably engages with the transverse bar of one reinforcing layer in use and the side or face at the other longitudinal end of each projection preferably engages with the transverse bar of the other reinforcing layer in use.

The connector of the invention preferably further comprises a securing plate which is adapted to mount across a plurality of projections in a securing position, after engagement of the projections with the or each reinforcing layer, to prevent disengagement of the reinforcing layer(s) from the projections. This aspect of the invention permits pretensioning without any potential slack, and allows fills to be placed over the connected geogrid system by securing the grids together on the connector which could otherwise come free.

The securing plate preferably has a plurality of spaced apertures corresponding to the spacing of the projections of the base, the securing plate being configured to locate over the projections in the securing position.

The cross-section of the securing plate apertures preferably corresponds substantially to the cross-section of the projections on the base. The securing plate may mount to the projections by means of an interference fit, or by means of ratchet ribs. The ribs may be provided on the projections, on the securing plate aperture edges, or both.

The securing plate is preferably substantially planar. The apertures on the securing plate are preferably resiliently spaced from one another to allow for variation in the spacing between the projections on the base. In one preferred embodiment, the securing plate comprises a plurality of resiliently-interconnected plate sections with an aperture provided in each. The plate sections are preferably interconnected by resilient elements, which may comprise curved spring elements. The elements are able to compress or expand to adjust the spacing between each

section/aperture.

Any suitable material may be employed to make the securing plate, including plastics or metal, but preferably the plate is formed from high density polyethylene (HDPE) or polypropylene.

The invention may also extend to the combination of a connector as described above and a reinforcing layer, such as a uniaxial or biaxial geogrid. The invention also provides a system for securing a retaining wall. A method of securing a connector to a reinforcing layer and a method of connecting two reinforcing layers are also provided.

At least in its preferred embodiments, the present invention provides a connector which provides a full strength mechanical connection without any slack, unlike the prior art method for connecting two geogrids described above. The connector also accommodates different thicknesses and strengths of reinforcing layer, or reinforcing layers from different manufacturers.

The resilient spacing of the projections (and optionally the apertures on the securing plate) allows the connector to be adjusted depending on the exact spacing or pitch of the apertures of the reinforcing layer. This avoids a concentration of stress at contact points if the pitches are not exactly matched.

Brief Description of the Drawings

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figs. 1 and 2 show in elevation and plan view respectively a reinforced panel retaining wall system with geogrids interconnected by a connector in accordance with the invention;

Fig. 3 shows an elevation view of a segmental block retaining wall with a connector in accordance with the invention being used to connect a geogrid to the wall;

Fig. 4 shows a connector in accordance with the invention in plan, side elevation and end elevation;

Fig. 5 shows a securing plate for use with a connector in accordance with the invention; and Fig. 6 shows an enlarged detail view of the connector of the invention in use to connect two geogrids together.

Detailed Description of a Preferred Embodiment

Figs. 1 and 2 show in elevation and plan view respectively a reinforced panel retaining wall system The retaining wall comprises a panel 10 formed from cast concrete 11 reinforced with horizontal and vertical rebars 12. Before the concrete is cast around the rebars, one or more panel geogrids 20 are connected to the rebars by inserting the rebars through apertures of each geogrid (Fig. 2). The formation of the panel with rebars and panel geogrids may be done remotely. As can be seen from Fig. 1, the geogrids 20 are provided at vertically-spaced intervals.

Further sections of geogrid, or site geogrids 30, are connected to the panel geogrids 20 by means of one or more connectors 100 in accordance with the invention, as described in more detail below. A tension force in the direction of the arrow T is therefore transmitted from geogrid 30 via the connector 100 to geogrid 20 and on to the retaining wall panel 10.

Fig. 3 shows an elevation view of a segmental block retaining wall 40 formed from rib blocks 41 and insert block 42.

Geogrid 50 is shown inserted between top rib block 41 and insert block 42. Geogrid 50 is the same as geogrids 20 and 30, and has transverse bars 51 interconnected by elongated high tensile ribs 52. Connector 100 in accordance with the invention is used to connect geogrid 50 to the retaining wall 40. Projections on connector 100 are inserted through the apertures between the elongate ribs 52 of geogrid 50, with transverse bar 51 in contact with the projections. A tension force in the direction of the arrow T is therefore transmitted via the connector 100 to the retaining wall 40.

As can be seen in Fig. 3, the connector 100 acts as an inter-block shear connector. Apertures in rib block 41 and insert block 42 accommodate the connector and are configured to lock the blocks together when the connector is present and tension in the direction of the arrow T is applied. Further space is provided to house the transverse bar 51 to avoid interference with block location. Elongate ribs of the geogrid 50 extend forwards from the apertures, between the blocks, to match the spacing at front and rear bed faces of the blocks, which maintains the blocks in parallel relation to one another.

Although not shown in Fig. 3, the securing plate 200 discussed below may be used in conjunction with connector 100 in this arrangement.

Fig. 4 shows a connector 100 in accordance with the invention in plan view, side elevation and through section A-A. The connector is unitary and is formed from HDPE or polypropylene. The connector 100 comprises a substantially planar base formed from a plurality of resiliently- interconnected base flanges 101. A projection 102 extends perpendicularly from each base flange 101. In use, as shown in Fig. 6, the projections 102 are inserted into and project through respective apertures of the geogrid and engage with a transverse bar of the geogrid so that a tension force is transmitted longitudinally from the geogrid to the connector. The base flanges 101 are interconnected by resilient curved spring elements 103 which are able to compress or expand to adjust the spacing between each projection 102, to allow for variation in the spacing of the apertures of the geogrid in the transverse direction.

In plan view, the cross-section of each projection 102 tapers in the longitudinal direction, either side of its transverse centre line, and is squared off at each longitudinal end. At least one of these longitudinal ends engages with the transverse bar of the geogrid in use. The projection 102 may taper vertically towards the end distal from the base flange 101 but it is preferably untapered to maintain contact with the geogrid for the majority of its height.

Ratchet ribs 104 are provided on the longitudinal end walls of each projection 102, for use with securing plate 200 discussed below. The ribs serve to lock the securing plate in position, and also allow different thicknesses or numbers of geogrids to be accommodated by the connector.

Fig. 5 shows a planar securing plate 200 for use with a connector 100 in accordance with the invention in plan view, side elevation and through sections A-A and B-B. The securing plate is unitary and is formed from HDPE or polypropylene. Securing plate 200 is adapted to mount across/onto a plurality of projections 102 in a securing position as shown in Fig. 6, after engagement of the projections with the or each geogrid, to prevent disengagement of the geogrid from the projections.

Securing plate 200 comprises a plurality of resiliently-interconnected plate sections 201 with an aperture 202 provided in each. The plate sections 201 are interconnected by resilient curved spring elements 203 which are able to compress or expand to adjust the spacing between each plate section/aperture. When no biasing force is applied, the spacing of the apertures corresponds to the spacing of the projections 102 of connector 100 (when similarly no biasing force is applied to connector 100). The cross-sectional shape of the securing plate apertures 202 corresponds substantially to the cross-sectional shape of the projections 102 on the connector 100. The securing plate 200 may mount to the projections 102 by means of an interference fit, or by means of ratchet ribs 104 discussed in relation to Fig. 4 above. As can be seen in the view of section A-A in Fig. 5, the internal longitudinal end walls of each aperture 202 have a taper which is narrower at the top surface than at the bottom surface. This provides a very secure attachment to the ratchet ribs 104. Means for identifying the correct orientation for the plate may be provided, such as an indication of the correct side to have uppermost. Fig. 6 shows an enlarged detail view of Fig. 1, showing the connector 100 and securing plate 200 of the invention in use to connect two geogrids 20 and 30 together.

The projections 102 are inserted through respective apertures of each geogrid 20, 30 when the layers are in an overlapping relation, the projections 102 engaging in use with a transverse bar 21, 31 of each geogrid so that a tension force is transmitted longitudinally from one geogrid to the other via the connector 100. The geogrids 20, 30 are secured onto the projections by securing plate 200 which slides down over the projections 102 and locks in place as discussed above.

Through the provision of resilient curved spring elements 103 and 203, the spacing between the projections 102 and the apertures 202 can be adjusted to match the spacing of the apertures in the geogrids 20 and 30.