GB2229475A

GB2229475A - Revetment blocks

Info

Publication number: GB2229475A
Application number: GB8906862A
Authority: GB
Inventors: David John Beerling
Original assignee: University College Cardiff Consultants Ltd; Cardiff University
Current assignee: University College Cardiff Consultants Ltd; Cardiff University
Priority date: 1989-03-23
Filing date: 1989-03-23
Publication date: 1990-09-26
Anticipated expiration: 2009-03-23
Also published as: GB8906862D0; GB2229475B

Abstract

The blocks comprise an upper stratum (1) and a lower stratum (2) which is integral therewith. The two strata are each typically squares of substantially the same edge length; the centre of square (2) being offset along the diagonal of square (1) relative to the centre of the latter square, such that there is a central square area (3) which is common to both strata; upper stratum has an L-shaped portion (4) overlapping the square area (3) and square (2) has a further L-shaped portion diagonally spaced from portion (4). The blocks can be laid in a space-filling fashion, with portions (4) overlapping complementary portions on adjacent blocks. <IMAGE>

Description

Revetment Blocks The present invention is concerned with revetment blocks for use on river banks or the like, or as surfacing for car parking areas or the like.

Revetment blocks are conventionally laid on river banks to stabilise the banks and to reduce the hydraulic roughness of the water channel. Current designs of such blocks generally include large voids within each block, these voids being back-filled with soil and grass seed, such that the grass grows to form an aesthetically pleasing grass-covered bank. Similar revetment blocks are used as surfacing for car parking areas and other similar areas where a stable support surface is required in which plant cover can grow.

It has been found that some vigorous species of tall perennials can grow through the voids and eventually displace the blocks. Of particular concern is the recent extension of the distribution of an introduced plant species, Japanese Knotweed (Reynoutria Japonica Houtt), which has caused many water authorities and landowners considerable concern: two or three seasons of growth of the Japanese Knotweed often results in block displacement with consequent high maintenance costs in replacing and relocating the displaced blocks.

It is an object of the present invention to provide an improved revetment block.

The block according to the invention comprises a first porous mineral stratum and, integral therewith, a second porous mineral stratum, the edges of which are substantially parallel to, but offset from, the edges of said first stratum such that said blocks can be laid with edges abutting and edge portions thereof overlapping, the pores in said strata being of sufficient size for the establishment and rooting of grasses therein but not for rooting of large-stemmed perennial plants.

When the strata are square or rectangular, it is preferred that the centre of gravity of the first stratum is offset along a diagonal of the second stratum relative to the centre of gravity of the latter stratum.

It is further preferred that both upper and lower strata are continuous, in the sense that there are no macro voids or discontinuities running between opposed major surfaces thereof.

It is particularly preferred that the revetment block according to the invention should be formed as a unitary body from "no-fines" concrete, which comprises stone chippings, mixed with cement and water (the cement to water ratio being typically 1:0.4 to 0.5, such as 1: about 0.45). The stone chippings are typically irregularly shaped limestone chippings, generelly having a maximum dimension of about 20mm.

("Fo-fines" concrete, as its name suggests, is essentially free of fine solids, such as sand).

The revetment blocks according to the invention typically have a pore volume of 35 to 45%, such as about 40X, and a minimum compression strength of at least 3.0 N per mm2 (such as about 3.5 E per mm2).

A preferred embodiment of the present invention will now be described, with reference to the accompanying drawings, in which: Figure 1 is a plan view of an exemplary revetment block according to the invention; Figure 2 is a side elevation of the block of Figure 1; Figure 3 is a plan view of an array of four revetment blocks as illustrated in Figure 1; and Figure 4 is a side elevation of a pair of overlapping revetment blocks.

Referring to the drawings, each block comprises an upper square stratum 1 and a lower square stratum 2 which is integral therewith. The two strata are each squares of substantially the same edge length; the centre of square 2 is offset along the diagonal of square 1 relative to the centre of the latter square. Thus, there is a central, square area 3 which is common to both strata; upper stratum has an L-shaped portion 4 overlapping the square area 3 and square 2 has a further L-shaped portion 5 diagonally spaced from portion 4.

Thus it can be seen from Figures 3 and 4 that the blocks can be laid in a space-filling fashion, with portions 4 overlapping complementary portions 3 on adjacent blocks.

By virtue of their monoblock construction and the arrangement of overlapping portions, there are effectively no suitable channels or voids for growth of large-stemmed plants from the underlying soil.

Of course revetment blocks with strata of shapes other than square are envisaged: for example, the strata may be rectangular, parallepipedal, triangular, L-shaped, trapezium-shaped or hexagonal. In another embodiment of the invention, there may be employed a combination of a first type of block with strata of a first shape and a second type of block with strata of a second shepe, provided that the two types of block can be arranged in space-filling array with overlapping edges.

Claims

Claims:

1. A revetment block which comprises a first porous mineral stratum and, integral therewith, a second porous mineral stratum, the edges of which are substantially parallel to, but offset from, the edges of said first stratum such that said blocks can be laid with edges abutting and edge portions thereof overlapping, the pores in said strata being of sufficient size for the establishment and rooting of grasses therein but for rooting of large-stemmed perennial plants.

2. A block according to claim I, in which said strata are square or rectangular.

3. A block according to claim 2, in which the centre of gravity of the first stratum is offset along a diagonal of the second stratum relative to the centre of gravity of the latter stratum.

4. A block according to any of claims 1 to 3, in which both upper and lower strata are continuous, such that there are no macro voids or discontinuities running between opposed major surfaces thereof.

5. A block according to any of claims 1 to 4, which is formed as a unitary body from stone chippings, mixed with cement and water.

6. A block according to claim 5, in which the cement to water ratio is 1: 0.4 to 0.5.

7. A block according to claim 5 or 6, wherein said stone chippings are irregularly shaped limestone chippings.

8. A block according to claim 7, wherein said limestone chippings have a maximum dimension not exceeding 20mm.

9. A block according to any of claims 1 to 8, which has a pore volume of 35 to 45%.

10. A civil engineering structure, which comprises a plurality of blocks according to any of claims 1 to 9, laid in space-filling fashion with first strata overlapping second strata in respective adjacent blocks.

11. A revetment block suitable for use as river bank surfacing, substantially as described therein with reference to the accompanying drawings.