WO2005011077A1

WO2005011077A1 - Protective strip for underground object

Info

Publication number: WO2005011077A1
Application number: PCT/AU2004/000992
Authority: WO
Inventors: Geoffrey Ian Jones
Original assignee: A.L.M. Industries Pty Ltd
Priority date: 2003-07-24
Filing date: 2004-07-23
Publication date: 2005-02-03
Also published as: NZ545369A; AU2003903830A0

Abstract

A hard plastic strip (4) is provided as protection and warning for an underground cable (1) or other utility service. The strip (4) has a wavy or other non-planar profile to facilitate if being embeded in bedding sand (3) directly above the cable, and thereby resist dislodgement from its position. The underside of one end portion of the strip is generally complementary to the topside of the other end portion. When a plurality of such strips (4) are laid in a line over the cable run with their adjacent end portions overlapped, the end portion of one strip nests with the end portion of an adjacent strip to resist lateral movement between them. The strips may also be laid side by side with their adjacent side portions overlapped, one side portion nesting with the side portion of an adjacent strip.

Description

"PROTECTIVE STRIP FOR UNDERGROUND OBJECT"

This invention relates to a protective strip for an underground object. In particular, the invention is directed to a non-planar strip of hard polymeric material suitable for burial above one or more underground cables or other services so as to protect such cables or services and/or to provide an indication of their presence.

BACKGROUND ART Electrical and telecommunications cables, water supply pipes, drainage pipes and other services are commonly installed underground. Flat elongate plastic strips are often laid over such services in order to protect them from damage by stakes or other items driven into the ground, and/or to provide a warning during subsequent excavations that there are buried services below. Typically, a cable or other service is laid on or near the bottom of an excavated trench. (For an electrical cable, the trench is normally around 600- 1200mm deep). The trench is then partially filled to a depth of around 150mm above the cable. Flat extruded plastic strips, typically 200mm wide and 1.2m long, are laid end to end on the fill over the cable. (Flat strips of other widths and lengths are also available). The trench is then backfilled to ground level. It has been found that such protective strips have several inherent disadvantages. First, the flat strips tend to slide out of position. This problem is exacerbated when the top surface of the initial fill is not level, and/or when operators walk in the partially-filled trench. Consequently, the strips are no longer located directly above the cable or other service, rendering the cable or service vulnerable to damage from stakes, posts and other sharp objects driven into the ground. Furthermore, the strips no longer provide an accurate warning as they do not faithfully indicate the lateral position of the cable or other service. Secondly, operators walking in the partially filled trench may slip on the smooth planar service of the strips, and risk injury. U.S. patent no. 5,962,809 discloses an underground cable protection system which comprises a plurality of inverted U-shaped channel sections laid end to end, with mechanical interconnecting means for joining opposed ends of adjacent channel sections. One or more cables are housed within the channel sections. The channel sections of this cable protection system retain their position relative to the cable(s) as they are extend around the cables. However, the separately manufactured mechanical interconnecting means adds to the cost of installation. Furtheraiore, the positive connection of opposed ends of adjacent sections with the interconnecting means is a time consuming process which increases the installation time. More importantly, as the channel sections are located immediately adjacent the cable(s), they do not give sufficient advance warning to an excavator of the presence of buried cable(s). There are known rigid UPVC cable cover sections manufactured by

Boddingtons which are designed to be buried above underground services. The cable cover sections have complementary male and female connections at opposite ends, and are designed to be connected end to end. However, the projecting male connectors are susceptible to breakage in use or transit. Consequently, as the juxtaposed ends of the cover sections are not joined or engaged, they can easily slip out off alignment with each other and with the buried cables. It is an aim of this invention to provide a protective strip for underground objects, and a method for installing a plurality of such strips, which overcome or ameliorate one or more of the disadvantages mentioned above.

SUMMARY OF THE INVENTION The invention provides a protective strip for an elongate underground object, such as a cable or other utility service, comprising a non-planar elongate member. In use, the non-planar profile assists the strip to embed itself, at least partially, in bedding sand or other particulate material in which the object is buried. Consequently, the protective strip resists dislodgement from its intended position above the object, and has greater stability than prior art flat strips. If installers walk on the protective strips during installation, it actually helps bed the strips firmly in position. The non-planar strip also has lower slip characteristics, rendering it safer for installers to walk on. The strip has opposite end portions, and opposite side portions. The underside of one end portion is generally complementary to the topside of the other end portion. In use, a plurality of such strips are laid longitudinally with their adjacent end portions overlapped. The end portion of one strip nests with the end portion of an adjacent strip, to resist lateral movement therebetween. Since the overlapped ends of a pair of adjacent strips nest or fit one within the other, they each assist the other to resist lateral dislodgement. Furthermore, the overlapping provides positive lateral location. The strips can be laid quickly and accurately as the ends are largely self -aligning. Preferably, the top side of said one end portion is also generally complementary to the underside of said other end portion. In this manner, the strips are reversible end to end. Preferably, the underside of one side portion is generally complementary to the top side of the other side portion. A plurality of such strips can be laid side by side with their adjacent side portions overlapped, one side portion nesting with the side portion of an adjacent strip to thereby resist lateral movement therebetween. Each strip assists the other to resist lateral dislodgement. Moreover, the laterally overlapped strips provide greater coverage, e.g. a wider profile to cover a plurality of cables or other services. The strip configuration defines the width of overlap, and ensures consistent overlap, thereby minimising wastage. Typically, the top side of said one side portion is generally complementary to the underside of said other side portion, so that the strip is reversible end to end. Advantageously, the protective strip has lateral edge portions which extend obliquely outwardly from the general plane of the strip. In use, the lateral edge portions extend downwardly and outwardly. When downward or lateral forces are applied to the strip, e.g. by additional fill material or by installers walking on the protective strips, these edges embed themselves in the bedding sand, thereby stabilising the strip against forces which would otherwise dislodge the strip from its intended position directly above the object. The strip is preferably of constant cross-section. In a preferred embodiment, the protective strip has a wavy sectional profile. The strip can be made by a thermo-moulding process. Typically, the strip is an extruded section formed of hard plastics or other synthetic non-conductive polymeric material. It is corrosion resistant and generally inert. The invention also provides a method of protecting an elongate underground object, such as a cable or other utility service, comprising the steps of placing a plurality of strips as described above in a line spaced at a predetermined distance directly above the object, and overlapping adjacent end portions of the strips so that the end portion of one strip nests with the end portion of an adjacent strip to resist lateral movement therebetween. The method may also comprise the steps of placing a second plurality of such strips laterally adjacent to the first plurality of strips, and overlapping adjacent side portions of the first and second plurality of strips so that the side portion of one strip nests with the side portion of a laterally adjacent strip to resist lateral movement therebetween. Typically, the object is laid in a trench and a layer of particulate material, such as bedding sand, is placed over the object to a desired height. The strips are laid on the layer of particulate material, and may be pushed into the particulate material so as to at least partially embed the strips in the material. The trench is then back-filled to ground level. The invention also provides a protective strip assembly for an elongate underground object, such as a cable or other utility service, the strip assembly comprising a plurality of strips as described above arranged longitudinally in a line directly above the object and spaced therefrom, the strips being positioned end to end with adjacent ends overlapped, such that the end portion of one strip nests with the end portion of an adjacent strip. The assembly may further comprise a second plurality of such strips positioned laterally adjacent to the first plurality of strips, with adjacent side portions of the first and second plurality of strips being overlapped so that the side portion of one strip nests with the side portion of a laterally adjacent strip, with precise and consistent overlap. In order that the invention may be fully understood and put into practice, preferred embodiments thereof will now be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig 1 is a schematic sectional view of a trench having a protective strip according to one embodiment of this invention. Fig 2 is an end view of the protective strip. Fig 3 is a perspective view of a plurality of the protective strips with overlapping ends. Fig 4 is a schematic sectional view of an overlapping portion of the strips. Fig 5 is a schematic sectional view of the bottom part of a trench having pairs of laterally overlapping protective strips installed above a plurality of cables. Figs 6 to 10 are schematic sectional views of protective strips according to alternative embodiments of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS As shown in Fig. 1, an electric cable 1 is laid in an excavated trench 2. (Preferably, the cable is laid on a layer of bedding sand above the bottom of the trench). The trench is then partially filled with soil 3 to a desired height above the cable run, usually 100-300mm and typically about 150mm. The soil 3 may be the excavated soil or it may be a sand fill. A plurality of strips 4 are then laid longitudinally in a line on the fill 3, directly above the cable 1. These strips are laid longitudinally end to end, with their ends overlapping as shown in Figs. 3 and 4. The strips 4 are then covered with additional soil 5 or other suitable fill, up to ground level. The strips 4 serve to protect the cable from damage from spikes, stakes, fence posts and other sharp objects driven into the ground. The strips 4 also protect persons from injury which might arise from a driven stake coming in contact with a live component of the cable. Further, the strips 4 serve as a warning during subsequent excavations, that a cable or other service lies directly below the strips. The strips 4 are shown in more detail in Figs 2 and 3. The strips are suitably made by a thermo-moulding process, such as extrusion. After each strip cools down following its extrusion, it adopts a stiff, quasi-rigid form. The illustrated strip 4 is an extruded length of non-conductive polymeric material, approximately 200mm in width and 5mm in thickness. It is manufactured and tested to Australian Standard AS 4702-2000. However, the invention is not limited to the illustrated embodiment, and the protective strips may be made in widths ranging from 100mm to 600mm, and in thicknesses ranging from 1mm to 10mm. The strips are typically made in lengths of 1.2m and 2.1m, but can be made in any suitable length. The strip 4 has a wavy cross section. Side edges 6,7 of the strip 4 are angled downwardly and outwardly, so that when downward pressure is placed on the strip 4, e.g. by walking on it, the side edges 6,7 embed themselves into the bedding sand 3 to retain the strip 4 in position over the cable run. Furthermore, the valleys 8,9 of the strip 4 also dig into the bedding sand 3 to help the strip resist forces which might otherwise displace it from its intended position. The strip 4 is substantially of constant thickness, and the profile of the upper surface of the strip 4 matches the profile of its lowers surface. In particular, the underside of one end portion of the strip is generally complementary to the topside of the other end portion. Consequently, when two such strips 4,4B are laid longitudinally with their adjacent end portions overlapped, as shown in Figs 3 and 4, the end portion of one strip 4 nests with the end portion of the adjacent strip 4B. This nesting overlap resists lateral movement between the two strips (particularly if the strips are constrained against vertical movement, e.g. by the weight of fill thereon). Hence each strip assists the other to resist forces which might otherwise displace the strip laterally from its intended position. In a further embodiment of the invention, strips may be overlapped laterally or transversely. To facilitate such lateral overlapping, the underside of one side portion of a strip is generally complementary to the top side of the other side portion. As shown in Fig. 5, when two such strips 4,10 are laid side by side with their adjacent side portions overlapped, one side portion of strip 4 nests with the side portion of an adjacent strip 10. Again, this nesting overlap resists lateral movement between the two strips (particularly if the strips are constrained against vertical movement, e.g. by the weight of fill thereon). Hence, each strip assists the other to resist forces which might otherwise displace the strip laterally from its intended position. Moreover, the laterally overlapped strips can be used to cover a plurality of cables 11 laid side by side which a single strip might not be able to span. (The cables may range from low voltage cables depicted by the smaller diameter circles in Fig 5, to high voltage cables depicted by the larger diameter circles in Fig 5). Note that the laterally overlapped protective strips may be identical strips, or may be non-identical strips 4,10 as shown in Fig. 5 (although the edge designs should be matching for positive overlap). The above described strips have several advantages, including:

• The non-planar wavy profile of each strip enables it to at least partially embed itself on top of the fill 3, and retain its position when the trench is filled to ground level.

• The profile of the strip 4 enables it to rest more securely on the fill 3, and resist dislodgement by operators walking in the trench 2, When stepped on, the strip embeds itself further in the fill. • The wavy nature of the strip 4 provides a non-slip surface for operators.

• Overlapping ends and/or side edges of the strips nest together to resist transverse slippage between adjacent strips.

• Where the end of one strip overlaps with, and nests with the adjacent end of the next strip, the strips are automatically and accurately aligned, thereby expediting the procedure of laying the strips over a cable run.

• The strips can be easily extruded to a non-planar shape.

• The strips are penetration resistant and shock absorbing, corrosion resistant and long lasting. Strips according to alternative embodiments of the invention are shown (in sectional view) in Figs 6 to 10. The non-planar cross-sectional profiles of the strips illustrated in Figs 6 to 10, and in particular their downwardly extending side edges, assist in maintaining the strips in position over the cable. All of the strips illustrated in Figs 6 to 10 can be overlapped longitudinally with nested ends. The strips illustrated in Figs 7, 8 and 10 can additionally be overlapped laterally. The foregoing only describes some embodiments of the invention and variations may be made thereto without departing from the scope of the invention. For example, although the protective/warning strips have been described with particular reference to their use with an electricity cable 1, it will be apparent to those skilled in the art that the strips can be used as protection or warning for other services, such as telecommunications cables, water supply pipes, underground drains and sewers. Each strip may optionally be provided with one or more holes for receiving a locating peg or clip pin.

Claims

1. A protective strip adapted for placement above an elongate underground object, such as a cable or other utility service, the strip comprising a non- planar elongate member having opposite end portions, characterised in that the underside of one end portion is generally complementary to the topside of the other end portion such that when a plurality of such strips are laid longitudinally with their adjacent end portions overlapped, the end portion of one strip nests with the end portion of an adjacent strip to resist lateral movement therebetween.

2. A protective strip as claimed in claim 1, wherein the top side of said one end portion is generally complementary to the underside of said other end portion.

3. A protective strip as claimed in claim 1, wherein the strip has opposite side portions, the underside of one side portion being generally complementary to the top side of the other side portion such that when a plurality of such strips are laid side by side with their adjacent side portions overlapped, one side portion nests with the side portion of an adjacent strip to resist lateral movement therebetween.

4. A protective strip as claimed in claim 3, wherein the top side of said one side portion is generally complementary to the underside of said other side portion.

5. A protective strip as claimed in claim 1, wherein the strip has lateral edge portions which extend obliquely outwardly from the strip, such that in use, the lateral edge portions extend downwardly and outwardly.

6. A protective strip as claimed in claim 1, wherein the strip is formed of hard thermo-moulded polymeric material.

7. A protective strip as claimed in claim 6, wherein the strip is an extruded section.

8. A protective strip as claimed in claim 1, wherein the strip has a wavy sectional profile.

9. A method of protecting an elongate underground object, such as a cable or other utility service, comprising the steps of placing a plurality of strips as claimed in claim 1 in a line spaced at a predetermined distance directly above the object, and overlapping adjacent end portions of the strips so that the end portion of one strip nests with the end portion of an adjacent strip to resist lateral movement therebetween.

10. A method as claimed in claim 9, further comprising the steps of placing a second plurality of strips as claimed in claim 1 laterally adjacent to the first plurality of strips, and overlapping adjacent side portions of the first and second plurality of strips so that the side portion of one strip nests with the side portion of a laterally adjacent strip to resist lateral movement therebetween.

11. A method as claimed in claim 9, wherein the strips are placed on a layer of particulate material over the object, further comprising the step of pushing the strips into the particulate material so as to at least partially embed the strips in the material.

12. A method as claimed in claim 11, wherein the strips each have lateral edge portions which extend obliquely outwardly from the strip, and the pushing step causes the lateral edge portions to be embedded in the particulate material.

13. A method as claimed in claim 9, wherein the strips are placed on a layer of particulate material over the object, further comprising the step of adding additional particulate material over the strips.

14. A protective strip assembly for an elongate underground object, such as a cable or other utility service, the strip assembly comprising a plurality of strips as claimed in claim 1 arranged longitudinally in a line directly above the object and spaced therefrom, the strips being positioned end to end with adjacent ends overlapped, such that the end portion of one strip nests with the end portion of an adjacent strip.

15. A protective strip assembly as claimed in claim 14, further comprising a second plurality of strips as claimed in claim 1 positioned laterally adjacent to the first plurality of strips, adjacent side portions of the first and second plurality of strips being overlapped so that the side portion of one strip nests with the side portion of a laterally adjacent strip.