GB2331317A

GB2331317A - Retaining wall system

Info

Publication number: GB2331317A
Application number: GB9724121A
Authority: GB
Inventors: John Alfred Fifield; Andrew Stuart Bedford
Original assignee: Forticrete Ltd
Current assignee: Forticrete Ltd
Priority date: 1997-11-14
Filing date: 1997-11-14
Publication date: 1999-05-19
Also published as: IE980908A1; CA2253147A1; GB9724121D0

Abstract

A retaining wall system including a set of blocks (10), geogrid connectors (30) and geogrid sheets (50) is provided, having means to redirect horizontally applied forces at least partially in a downwards direction. According to one embodiment, the blocks (10) have upper and lower channels which define an 'L' shaped conduit (55) between vertically adjacent blocks. An 'L' shaped connector (30) is provided for limited rotational movement in the channel, and is connected to the geogrid material (50). Upon the application of a horizontal force on the geogrid material, the connector rotates and applies downwards force to the block below it, thus increasing the effective weight of the wall and improving its stability.

Description

1 j 2331317 RETAINING WALL SYSTEM The present invention relates to a

retaining wall system and to blocks and geogrid connectors for use in such a system.

Retaining walls are commonly used in civil engineering structures and are generally built from blocks, usually of precast concrete, which are laid to form either a substantially vertical wall or one in which the wall has a batter angle greater than 0'. Most conveniently, the blocks are dry laid, usually in a broken bond arrangement.

As will be appreciated, such retaining walls are often required to withstand very high lateral pressure exerted by large volumes of backfill material. Not only must the walls be designed to withstand such pressure, but account must also be taken of anticipated pressure variations caused by swelling and/or shrinkage of the earth as its moisture content and temperature changes. Moreover, in areas where seismic activity is a risk, the walls should ideally be constructed to sustain the sudden and extremely high loads that may be encountered during earthquakes.

In order to improve the stability and strength of retaining wall structures, it has become common practice to utilise one or more sheets of mesh-like reinforcing material extending laterally from the wall through the backfill soil. This mesh-like reinforcing material is often referred to as "geogrid" material and a widely used form of geogrid material and its method of manufacture is disclosed in US patent no. 4374798. Preferably the geogrid sheets are secured in place by the blocks as the blocks are laid and the soil back filled, thereby creating a relatively stabilised soil structure. Depending on the local conditions, sheets of geogrid material may be laid between each course of blocks or between selected courses only.

Retaining walls have in the past been constructed with the end portions of the geogrid sheets being simply laid between courses of blocks and held in place by relying upon the imposed dead-weight of the overlying courses of blocks in the wall. The stability of 1 1 2 retaining walls constructed in this way may be compromised in the event of movement between the courses of blocks. This is because movement of the blocks results in abrasion of the grid material thus weakening the material and eventually resulting in its failure where it contacts the wall. If the movement is in the vertical direction, such as might be encountered during seismic activity, the connection between the grid and the blocks may become severed, albeit momentarily, so that the dead- weight of superimposed courses of blocks is rendered entirely ineffective. It will be appreciated therefore that simply laying the geogrid material between courses of blocks is not a reliably safe means of anchoring the earth behind a retaining wall.

In view of the inherent disadvantages of the aforementioned system, it has become more usual to provide attachment means to more firmly secure the geogrid sheets to the blocks thereby to reduce the possibility of the sheets becoming detached from the wall structure and countering the risk of the retained soil causing collapse of the wall.

Such means for attaching the geogrid sheets may be provided integrally with each of the blocks. For example, blocks in the form of precast concrete elements such as described in one of the embodiments of WO 94/13890 have connecting means in the form of a matrix of projections on the upper surface of the blocks with their lower surface including recesses. The retaining wall is constructed from layers of such blocks so that the recesses of one tier of blocks receive the projections of an adjacent tier; in this way, the projections act to secure the geogrid material and to align the layers with each other. Such projections, being adapted to protrude through the mesh of the grid-like reinforcing material, can be formed in the concrete during the block making process or embedded therein before the concrete is cured.

The process for manufacturing concrete blocks is of course highly automated and the rate of production of a single block unit is generally only a few seconds. Consequently, the need to provide connecting means on the blocks themselves complicates the block production process resulting in inefficient utilisation of conventional block making machines. Moreover, the projections are liable to damage during manufacture, packing and installation when these are formed of concrete. While projections created by 3 embedding separate elements in the blocks during manufacture can be made of a durable material, modification of the blocks in this way prior to curing still suffers from drawbacks in terms of loss of efficiency in the block production.

A flirther disadvantage of the aforementioned system is that the integral projections are often wider than the apertures in the geogrid material. This means that the geogrid apertures must be enlarged by severing one or more adjacent ribs so that the projections are able to protrude through. Cutting of the ribs to provide sufficiently large apertures to receive the blocks' projections effectively reduces the strength of the geogrid material at the positions where it is subject to maximum load, namely at the point of contact between the projections and material bounding the grid apertures.

Other means of securing the geogrid material to the blocks have been developed. One such means involves the provision of bores extending inwardly from both upper and lower surfaces of the blocks and into which connecting pins are inserted. In constructing a wall from such blocks, a first course of blocks is laid, connecting pins are then inserted into the upper surface bores and the geogrid material is then laid over the pins so that the pins protrude through the mesh. A second course of blocks is then laid on top of the first course so that the pins enter the bores provided in the lower surface of the second course blocks. In this way, the pins serve both to secure the geogrid material in position and to align the block layers.

The use of such connecting pins is not, however, without disadvantages. The additional steps required to produce blocks with such bores still compromises the efficiency of block manufacture and the requirement for positive location of the overlying blocks on the pins slows down the rate at which the retaining wall can be constructed.

Moreover, it is usual for the pins to be spaced apart so that not all of the apertures along a line of grid material receives a pin. Again, this means that the strength of the geogrid material is not fully utilised, since many apertures are devoid of connecting pins.

4 Attempts to overcome many of the problems associated with each of the aforementioned retaining wall systems have resulted in the development of a system in which the blocks are each formed with an upper channel in a top surface thereof and a lower channel in the bottom surface thereof, the upper channel in a lower course aligning with the lower channel in an adjacent upper course such that together they define a conduit for accommodating a separate geogrid connector. This connector takes the form of a rake-like element, the teeth of which serve to hold the geogrid material by projecting between the material's apertures. One such system is disclosed in US patent no. 5,417,523.

During construction of the wall according to this system, a course of blocks is laid and a connector is positioned in the upper channel. A sheet of the grid-like material is then laid over the connector so that its teeth protrude through the grid adjacent one edge of the sheet to hold the sheet in position. A further course of blocks is then laid on top so that its lower channel is aligned with the upper channel of the course below, effectively "trapping" the connector and hence also an elongate edge of the geogrid material between the courses. Layers of rocks, earth or other backfill material are preferably deposited over each grid as the number of courses builds up. By such means, the connector connects the grid-like material to the wall and the grid-like material in turn distributes the load of the backfill material substantially evenly across the wall.

While such a system is able to withstand the reasonably high lateral pressures exerted by the weight of backfill material, owing to the fact that the system relies only upon the imposed dead-weight of the wall to retain its integrity, the system is still not as safe as it might be when it is subjected to sudden and/or abnormal ground movement, such as might be encountered during seismic activity or during periods of severe drought or heavy rainfall.

Thus, despite plenty of retaining wall systems being available, there is still considerable room for improvement when it comes to stability, especially during periods of unusual ground movement. It is therefore an object of the present invention to provide a modular retaining wall system comprising a plurality of blocks and geogrid connectors which when assembled form a retaining wall having improved stability under nonstatic conditions.

It is a further object of the invention to provide a block for use in such a retaining wall system which is capable of being simply produced on conventional block making equipment.

Another object of the invention is to provide a geogrid connector adapted for use with the blocks of the aforementioned retaining wall system.

Accordingly, from a first aspect, the invention resides in a retaining wall system comprising a plurality of blocks and geogrid connectors, wherein the blocks and connectors are adapted to co-operate with each other in use at least partially to translate a lateral force acting on the wall into a downward force.

In general, when the backfill or otherwise retained earth is subjected to ground heave or shrinkage, or to other sorts of ground movement, the pressure against the rear face of the retaining wall will inevitably increase. At least a component of this pressure or force will be in the horizontal direction relative to the wall. This horizontal force will in turn cause one or more of the sheets of geogrid material to exert an opposing horizontal force on the geogrid connector. By means of the invention, the geogrid connector co-operates with one or more adjacent blocks in the wall in such a way as to dissipate the applied horizontal force by converting it at least partially into a downward force. This downward force is additional to the downward force resulting from the dead-weight of the wall itself. Thus it will be appreciated that by virtue of the invention, the stability of the retaining wall is enhanced when the wall is subjected to abnormal pressure.

Expressed in a different way, the invention resides in a method for increasing the effective weight of a retaining wall wherein a horizontal force acting on the wall is converted at least partially to a downward force thereby enhancing the applied force of the deadweight of the blocks in the wall.

6 In accordance with a preferred embodiment, the blocks are generally provided with an upper channel on their top surface in use and a lower channel on their bottom surface in use such that when the blocks are laid to form a wall, the upper and lower channels of the blocks in adjacent courses are aligned to create a receiving conduit for retaining the geogrid connector. Moreover, the conduit is preferably adapted to permit the connector to turn when under an applied lateral force whereby to cause a lower portion of the connector to press downwardly against an upwardly directed surface on an underlying block. By virtue of this action, the connector and blocks interact to convert a substantially horizontal force into a vertical force. Conveniently, the upwardly directed surface against which the lower portion of the connector presses upon turning comprises the base of the upper channel.

As will be appreciated, the turning moment of the connector increases as the lateral force on the wall and hence on the geogrid material increases, thus the greater the lateral pressure acting on the wall, the greater becomes its effective weight.

The permitted angular movement of the connector may be determined by the connector's shape and the shape of the conduit in which it is retained. Preferably, the degree of turning is limited by an upper portion of the connector coming into contact with a downwardly directed block surface. In other words, the connector can turn only as far as a position where upper and lower portions of which contact respectively downwardly and upwardly directed surfaces of one or more blocks.

Of course, while the upwardly directed surface of the block against which a lower portion of the connector will press upon turning will inevitably comprise a part of the immediately underlying block, the downwardly directed surface against which an upper portion of the connector will press upon turning may comprise a part of an immediately overlying block or, more preferably, may comprise another part of the same underlying block.

In the former case, it will be appreciated that as well as the lateral force being converted to a downward force caused by a lower portion of the connector pressing down against an 7 underlying block, an upward force will also be created by virtue of an upper portion of the connector pressing upwards against an overlying block.

In order therefore to avoid adding to any upward forces which may already be present by virtue of abnormal or sudden ground movement in the vicinity of the wall, the downwardly directed surface against which an upper portion of the connector presses upon turning is preferably provided on the same underlying block on which is provided the upwardly directed surface.

More particularly, the upper channel of the block into which the connector is laid during construction of the wall advantageously comprises a keyway which is adapted to receive the connector and provide both the upwardly and downwardly directed surfaces against which parts of the connector press at the point of maximum angular movement. For example, the keyway is substantially L-shaped in cross section so that the base of the 'U' forms the upwardly directed surface against which a lower portion of the connector presses upon turning and the underside of the arm of the 'U' provides the corresponding downwardly directed surface.

The base of the upper channel which advantageously constitutes the aforementioned upwardly directed surface may be substantially flat. Preferably, however, the base is gently ramped or inclined upwards from a position intermediate the channel's front and back walls towards the rear face in use of the block. In this way, the undersurface of the connector base if flat will contact the channel base only at its edges thus encouraging pivoting of the connector in the channel upon application of a lateral force.

To reduce or guard against the risk of the keyway becoming damaged when under pressure exerted by the connector as it tums and to allow room for the angular movement, the overall depth of the channel will usually be greater than that normally encountered on prior art retaining wall blocks.

Similarly, the connector should desirably have a profile which not only is able to accommodate a certain degree of angular movement but also allows relatively easy 8 insertion into the keyway. At the same time, it is also desirable that the connector be so configured as to prevent its withdrawal from the keyway upon its turning in response to a lateral force on the geogrid material.

In this regard, most connectors hitherto used in retaining wall systems have consisted essentially of an elongate bar forming a base which sits in the upper channel provided on a top surface of a block. A series of upwardly directed projections extend from a top surface of the base, usually at about 90' thereto, to project through the apertures in the geogrid sheet when the sheet is laid over the projections. In use, the projections stand proud of the upper channel but are enclosed by the lower channel on the bottom face of an adjacent block when the next course of blocks is laid.

While such a connector may be suitable for use in a retaining wall system according to the present invention, when the connector is intended for use in a keyway, its base is preferably angled to facilitate its insertion. For example, the base may be of a substantially open "V' shape in cross-section, a first arm of the 'V" adapted to lie in a generally horizontal plane with the second, adjoining arm extending at an angle of greater than 90' but less than 180' thereto. An angle of between about 120' and 150% more preferably about 135% being particularly suitable. The series of projections for holding the geogrid material preferably extend in an upward direction from the second arm, most preferably in a substantially vertical direction relative to the first arm.

From another aspect therefore, the invention flirther resides in a geogrid connector for use in a retaining wall system, the connector comprising a base and a series of upwardly directed projections, wherein the base is angled to facilitate its insertion into a keyway provided on a top surface in use of a block fonning a component of the system. Preferably the angled base of the connector comprises an open 'V' shape in cross section.

It is possible to improve the strength and rigidity of the aforementioned preferred connector without detriment to its convenience in use by making the second arm thicker in cross-section than the first arm. This is particularly preferred when the junction of the first and second arms of the connector base constitutes an edge which acts as the lower 9 portion of the connector for pressing downwardly against the underlying block. It is of course at this edge where at least a part of the lateral force acting on the geogrid material is converted to a downwardly directed force. By making the second arm relatively thicker than the first arm, the connector is effectively strengthened at a position where it might otherwise comprise a region of weakness.

In order to further reduce or substantially eliminate the possibility of the sheet of geogrid material becoming detached from the connector in use and to assist in keeping the sheet in position as each course of blocks is laid, it is advantageous to provide one or more of the upwardly directed projections with extension pieces, extending at an angle to the projections, and which together with the projections form hook elements. Preferably the or each extension piece element extends in a direction towards the front face of the block, that is, in the direction opposite to the direction in which the geogrid material extends.

The upwardly directed projections provided on the connector are generally spaced at intervals to suit the particular geogrid material with which it is to connect. In order to derive maximum benefit from the strength of the geogrid material, it is preferable that the projections are uniformly spaced and correspond to the spacing of the apertures in the geogrid material. Moreover, the projections ideally have smooth contours so as to avoid abrasion on the geogrid material. A connector provided with upwardly directed projections in the form of rounded pegs is particularly preferred.

Usually a plurality of connectors will be employed along a row of blocks in the same course. Each connector may conveniently have a width the same as the block width or a multiple thereof. In this way, there is no need to cut the "end" connectors to the right width during construction of the wall.

Apart ftom the ability to dissipate a lateral force acting against the retaining wall by converting it at least partially into a downward force, it is clearly advantageous for the retaining wall system of the invention also to incorporate means for countering an upward or uplifting force acting on the wall. In this regard, the blocks of the retaining wall system are preferably provided with further co-operating means whereby an upward force acting on an overlying block is at least partially transferred to an adjacent underlying block in the wall.

Most conveniently, the upper surface in use of a block is provided with a projection or a recess which is adapted respectively to overlap laterally with a co-operating recess or a projection provided on the lower surface in use of a block in an upwardly adjacent course. Preferably, the upper surface of the block is provided with a projection and the bottom surface with a recess. By such means, an uplifting force acting upon an overlying block in the wall will in turn result in engagement of the laterally extending projection of the underlying block in its recess thereby causing the underlying co-operating block also to lift. As will be appreciated, this action and reaction will cascade down through the courses of the wall and, as a consequence, the wall will effectively become locked. In this way, the risk of any individual course of blocks slipping under any coincident horizontal forces which may also be acting may be eliminated or at least substantially reduced.

In one embodiment, the co-operating projections and recesses are provided in the form of complementary angled surfaces on the top and bottom faces in use of the blocks. In an alternative embodiment, the projection on the top face comprises an interlocking rib and the recess on the bottom surface comprises a complementary keyway, for example, the rib and keyway may be substantially L-shaped in cross-section. Equally, the bottom face may be provided with such an interlocking rib and the top face with a complementary keyway.

Of course, it is important that any projection formed on the top surface in use of the block does not interfere with or otherwise obstruct the geogrid material when this is positioned on the connector resting on or held by the block during construction of the wall. Similarly, it would not be appropriate for any projections formed on the bottom surface of a block to interfere with the geogrid material when the block is laid over the connector on an adjacent lower course. In this regard, any projection formed on the top or bottom block surface is preferably located closer to the front face in use of the block, that is face which is exposed on the outer face of the wall, with the upper and lower channels for receiving the connector located closer to the rear face of the block. In this way, the geogrid material has an unobstructed "path" from its position on the connector as far as the rear face of the retaining wall and then into the retained earth behind the wall.

To assist in constructing a retaining wall, it is desirable that the blocks be provided with locating means so that as each course of blocks is laid, the blocks of one course can be readily and accurately aligned with the blocks in an underlying course. The use of complementary profiles on opposing top and bottom faces of each block represents one of the simplest means of achieving this aim. However, in accordance with a preferred aspect of the invention, the aforementioned further co- operating means for transferring an upward force acting on a block to an adjacent underlying block also serves as the locating means for aligning the blocks.

0 Apart from the desirability of ensuring that there are no obstructions in the way of the geogrid material where it lies in use between blocks in adjacent courses, it is advantageous to actually provide a gap between the top and bottom faces of blocks in the region where the geogrid material resides thereby to avoid or reduce weakening or otherwise damaging the geogrid material in the event of relative movement between the blocks.

One of the most important and valuable aspects of the blocks forming part of the retaining wall system of the invention is that they may be easily produced on conventional block making equipment. For example, there is no need for retractable side cores nor for modification of the block between forming and curing. The modular blocks according to the invention may therefore be produced economically.

Accordingly, from a yet further aspect, the invention resides in a modular block for a retaining wall system wherein the block is adapted to co-operate in use with a geogrid connector to convert a horizontal force acting on the wall at least partially into a downward force.

More particularly, the invention resides in a block for a retaining wall system, the block comprising a front face and a rear face, a top face and a bottom face, the top face being 12 provided with an upper channel and the bottom face with a lower channel such that when two such blocks are laid one on top of another in a retaining wall the upper and lower channels communicate to provide a conduit for retaining a geogrid connector, wherein the conduit is adapted to co-operate in use with a geogrid connector thereby at least partially to translate a lateral force acting on the wall into a downward force.

Preferably the upper channel of the block comprises a keyway, more preferably an Lshaped keyway, for receiving a base portion of a geogrid connector.

It is also preferred that the top and bottom faces of the block be provided with flu-ther means for co-operating with adjacent overlying and underlying blocks in a wall thereby to transfer at least partially an upward force acting on an overlying block in a wall to an adjacent underlying block.

As previously described, in a preferred embodiment, the block is provided on its top face with a projection or a recess adapted to overlap laterally with a co-operating recess or projection provided on a bottom face of a block in an adjacent overlying course. It will be understood therefore that each block will have on its top face a projection or recess (or both) and on its bottom face a co-operating recess or projection (or both).

More preferably, the laterally co-operating means provided on the top and bottom face of each block comprise projections and recesses having complementary angled surfaces. Alternatively, one of the faces may include a rib portion and the opposite face a complementary keyway.

By means of the invention, most notably the interaction between the blocks and the geogrid connector, it possible to construct a retaining wall which has superior properties in terms of its ability to resist collapse when subjected to abnormal pressure. The retaining wall system of the invention is therefore particularly suited for use in areas where ground movement is likely to occur, such as in regions prone to seismic activity.

13 Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

Fig. 1 is a perspective view of a retaining wall block in accordance with one aspect of the invention; Fig. 2 is a perspective view of a geogrid connector in accordance with another aspect of the invention; Fig. 3 is a series of partial end views showing stages of insertion of the geogrid connector of Fig. 2 in a block of Fig. 1; Fig. 4 is an end view of a plurality of blocks and connectors according to Figs. 1 and 2 in a retaining wall assembly; Fig. 5 is an end view of a pair of blocks and connectors in a retaining wall assembly and in which the blocks have alternative engagement means to the block of Fig. 1; Fig. 6 is a perspective view of an alternative geogrid connector; and Fig. 7 is an end view of a pair of blocks according to Fig. 1 and a pair of connectors according to Fig. 6 in a retaining wall assembly.

Turning first to Fig. 1, there is illustrated a retaining wall block 10 having a front face 11 which presents the exposed face of a retaining wall and a rear face 12 against which retained earth generally lies following construction of the wall.

The block 10 is provided on its top face 14 with an upper channel in the form of an Lshaped keyway 15 for receiving at least the base portion of a geogrid connector (not shown). The keyway 15 has both an upwardly directed surface 17 and a downwardly directed surface 18 each of which will co-operate with the connector to limit its degree of rotation. The block10 is also provided on its bottom face 19 with a lower channel in the 14 form of recess 20 which, when laid over another such block 10, communicates with keyway 15 to provide a conduit in which a connector may be retained. Also provided on the top face 14 of the block 10 is a projection 22 having a sloping surface 23 and on the bottom face 19 is provided a corresponding recess 24 having an complementary sloping surface 25.

The overall shape of the block 10 is such that it may simply produced on a conventional block making machine with end face 27 forming either the top or bottom face as made, with front and rear faces 11, 12 and top and bottom faces 14, 19 being shaped by the walls of the block mould.

Fig. 2 shows an elongate geogrid connector 30 for use with the block 10 of Fig. 1. The connector 30 has a base 32 which is of a generally open Vshape in cross-section, a first arm 34 providing a flat undersurface 35 and a second arm 36 extending at an obtuse angle thereto. The second arm 36 is made thicker than the first arm 34 to provide added strength. A plurality of regularly spaced round pegs 38 extend upwards from the second arm 36 at right angles to the first arm 34.

Insertion of the geogrid connector 30 of Fig. 2 into the keyway 15 of the block 10 of Fig. 1 is shown in stepwise sequence in Fig. 3. Initially, in step 1, the first arm 34 of connector 30 is introduced into keyway 15. In step 2, further insertion together with clockwise movement (as viewed from the direction of end face 27) of the connector 30 brings the first arm 34 under the overhang comprising downwardly directed block surface 18 of the keyway 15. Step 3 shows the connector 30 fully inserted in the keyway 15.

It will be seen from Fig. 3 that the effective width of the connector 30 is such that it cannot be lifted out of the keyway 15 in a substantially vertical direction without concurrent counterclockwise movement. Once in its normal position, as shown in step 3, a sheet 50 of geogrid material is laid over the connector 30 so that pegs 38 protrude through the apertures in the geogrid material. After this step, the block 10 is ready to receive a similar such block 10 laid on its upper surface 14 and a layer of earth or other infill material can be spread over the sheet 50 behind the rear face of the wall.

From the drawing of step 3, it can be seen that the upwardly directed surface 17 consists of a substantially horizontal firont portion 46 and an upwardly inclined rear portion 48. The flat undersurface 35 of the connector 30 will therefore only be able to contact the surface 17 at its extreme forward and rear edges.

An array of blocks 10 in a retaining wall assembly is illustrated in Fig. 4. A connector 30 is retained in each of the keyways 15 with the projections 38 standing proud of the top face 14 of each respective block 10 and sheets 50 of geogrid material are laid such that the projections 38 protrude through apertures in the material- Keyways 15 and recesses 20 on adjacent blocks together form a conduit 55 enclosing the connectors 30.

When a lateral force is applied to the rear faces 12 of the blocks 10 of the wall, this results in an equal but opposite force on the sheets 50 of geogrid material- Such a force will in turn act upon the connectors 30 as the sheets 50 are pulled against the pegs 38. This pulling against the pegs 38 will tend to turn the connectors 30 bringing lower edges 60 of the connectors 30 to press against rear portions 48 of the upwardly directed undersurfaces 17 and, at the maximum permitted extent of angular movement, upper edges 62 to press against the downwardly directed block surfaces 18. This pressing of a lower edge 60 of the connector 30 against an underlying block 10 enhances the applied force of the deadweight of the overlying blocks 10.

The projections 22 and recesses 24 not only facilitate alignment of the blocks 10 in adjacent courses but enable dissipation or re-distribution of an uplifting force acting on an overlying block to an underlying block by virtue of the inter-engagement between respective sloping surfaces 23, 25.

In order to reduce the risk abrasion of the sheets 50 of geogrid material between adjacent blocks 10 in the array, the top face 14 of each block is staggered so that the region 80 adjacent the rear face 12 of the block and over which the sheet 50 lies is lower and creates a gap 82. The sheets 50 extend laterally through the gaps 82 and so are not crushed between the blocks.

16 Instead of sloping surfaces 23, 25, as shown in Fig. 5 each blocks 10 may be provided with laterally overlapping means in the form of an L-shaped rib 70 provided on the top face 14 of the block 10 and a corresponding L- shaped keyway 72 provided on the bottom face 19. The width of the keyway 72 is greater than the width of the rib 70 in order to enable insertion of the rib 70 into the keyway 72.

Fig. 6 shows a connector similar to that of Fig. 2 except that pegs 38 are provided at their upper ends with extension pieces 90 which together with the pegs 38 form a series of hooks. As will be seen from Fig. 7, the extension pieces 90 provide added security to ensure the sheet 50 of geogrid material does not become detached from the connector 30.

Although the invention has been particularly described, it should be appreciated that the scope of the invention is not limited to the particular embodiments illustrated. Modifications and variations are therefore included within the scope of the invention. For example, while the retaining walls as illustrated form a substantially vertical structure, the block alignment may be off-set in order to produce a wall having a positive batter angle.

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Claims

A retaining wall system comprising a plurality of blocks and geogrid connectors, wherein the blocks and connectors are adapted to co-operate with each other in use at least partially to translate a lateral force acting on the wall into a downward force.
2. A retaining wall system according to claim 1, wherein each block comprises a top surface in use provided with an upper channel and a bottom surface in use provided with a lower channel such that when a plurality of such blocks are stacked to form a wall, the lower channel of one block is aligned with the upper channel of an underlying block to create a receiving conduit for retaining a geogrid connector, characterised in that the conduit is adapted to permit turning of the connector when under an applied lateral force whereby to cause a lower portion of the connector to press downwardly against an upwardly directed surface on an underlying block.
3. A retaining wall system according to claim 2, wherein the upwardly directed surface against which the lower portion of the connector presses upon turning comprises the base of the upper channel.
4. A retaining wall system according to claim 2 or 3, wherein the degree of angular movement of the connector is restricted by means of an upper portion of the connector contacting a downwardly directed block surface.
5. A retaining wall system according to claim 4, wherein the downwardly directed block surface is provided on the underlying block.
6. A retaining wall system according to any of claims 2 to 5, wherein the upper channel comprises a keyway.
7. A retaining wall system according to claim 6, wherein the keyway is substantially L-shaped in cross-section.

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8. A retaining wall system according to any of claims 3 to 8, wherein the base of the upper channel is inclined upwards from a position intermediate position the channel's front and back walls in the direction of the rear face in use of the block.
9. A retaining wall system according to any preceding claim, wherein the blocks are provided with further co-operating means whereby an upward force acting on an overlying block in a wall is at least partially transferred to an adjacent underlying block in the wall.
10. A retaining wall system according to claim 9, wherein the upper surface in use of each block is provided with a projection and the lower surface in use is provided with a recess which is adapted to overlap laterally with a corresponding projection on an immediately underlying block in the wall.
11. A retaining wall system according to claim 10, wherein the projection and the recess on each block comprise complementary angled surfaces which overlap laterally when a plurality of such blocks are stacked in a vertical array.
12. A retaining wall system according to claim 10, wherein the projection comprises a rib and the recess comprises a complementary keyway for interlocking with the rib.
13. A retaining wall system according to claim 12, wherein the rib and the keyway are substantially L-shaped in cross-section.
14. A modular block for a retaining wall system, characterised in that the block is adapted to co-operate in use with a geogrid connector to convert a horizontal force acting on the wall at least partially into a downward force.
15. A modular block according to claim 14 comprising a front face and a rear face, a top face and a bottom face, the top face being provided with an upper channel and the bottom face with a lower channel such that when two such blocks are laid one on top of another in a retaining wall the upper and lower channels communicate to provide a 19 conduit for retaining a geogrid connector, wherein the conduit is adapted to co-operate in use with a geogrid connector thereby at least partially to translate a lateral force acting on the wall into a downward force.
16. A modular block according to claim 15, wherein the upper channel comprises a keyway for receiving a base portion of a geogrid connector.
17. A modular block according to any of claims 14 to 17, wherein the block is provided with means for co-operating with adjacent overlying and underlying blocks in a retaining wall thereby to transfer at least partially an upward force acting on an overlying block in the wall to an adjacent underlying block.
18. A modular block according to claim 17, wherein said co-operating means comprises a projection provided on the block's upper surface in use and a recess provided on the block's lower surface in use and wherein the recess is adapted to overlap laterally with a corresponding projection on an immediately underlying block in the wall.
19. A modular block according to claim 18, wherein the projection and the recess include complementary angled surfaces to provide lateral overlap between vertically adjacent blocks in the wall.
20. A modular block according to claim 18, wherein the projection comprises a rib and the recess comprises a complementary keyway for interlocking with the rib.
21. A modular block according to claim 20, wherein the rib and the keyway are substantially L-shaped in cross-section.
22. A geogrid connector for use in a retaining wall system comprising a base member and a series of upwardly directed projections, wherein the base member is angled to permit insertion into a keyway provided on a top surface in use of a block forming a component of the system and to permit a degree of angular movement within the keyway.
23. A geogrid connector according to claim 22, wherein the angled base member comprises in cross-section first and second arms extending in a substantially open Vshape relative to each other.
24. A geogrid connector according to claim 23, wherein the first arm of said base is adapted to lie in a substantially horizontal plane in use and the second arm extends from the first arm at an obtuse angle thereto and wherein the series of upwardly directed projections extend from the second arm in a substantially vertical direction relative to the first arm.
25. A geogrid connector according to claim 23 or 24, wherein the second arm is thicker in cross-section than the first arm.
26. A geogrid connector according to any of claims 23 to 25, wherein the junction of the first and second arms on the underside in use of the base member comprises an edge which in use presses down against an underlying block in a retaining wall thereby to convert at least partially a lateral force acting on the connector into a downward force.
27. A geogrid connector according to any of claims 23 to 26, wherein one or more of the upwardly directed projections is provided with an extension piece, extending at an angle to the projection, and which together with the projection forms hook element.
28. A geogrid connector according to claim 27, wherein the or each extension piece extends in use in a direction towards the front face of the block.
29. A retaining wall when constructed from a retaining wall system according to any of claims 1 to 13, or when incorporating a plurality of modular blocks according to any of claims 14 to 2 1, or when incorporating a geogrid connector according to any of claims 22 to 28.

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30. A method for increasing the effective weight of a retaining wall wherein a horizontal force acting on the wall is converted at least partially to a downward force thereby enhancing the applied force of the dead-weight of the blocks in the wall.
31. A retaining wall system substantially as hereinbefore described with reference to Fig. 3 or 4 of the accompanying drawings.
32. A modular block for a retaining wall system substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings, or when modified according to Fig. 5.
33. A geogrid connector for a retaining wall system substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.