DEVICE AND METHOD FOR INDICATING UNDERGROUND OBJECT

Abstract: A tape (3) comprises a biodegradable carrier and a water soluble dye, and is buried in soil (4) above a service such as a pipe (2). The tape (3) may comprise ethylene vinyl acetate copolymer made biodegradable by the presence of starch. Upon biodegradation of the tape, the water soluble dye dissolves in soil moisture and diffuses in the soil above and below the original position of the tape. When it is desired to uncover the service (2), the soil is removed until the coloured band of soil is uncovered. This gives a warning that the service is positioned immediately below the coloured band of soil.

Description: DEVICE AND METHOD FOR INDICATING UNDERGROUND OBJECT The present invention relates to a device and method for indicating the presence of an underground service or other underground object. The underground service may comprise electrical power cables, gas lines, water and sewage pipes, transmission lines, and like installations which are commonly run beneath the surface of the ground between terminals or outlets. It is well known that such services are often required to be located and accessed, for example for maintenance or repair work to be carried out. In such circumstances, an excavator may have only an approximate guide to the position of the service to be accessed. Accordingly, it is desirable to provide some form of positive indication to the excavator as to the position of the service once excavation has commenced. Another circumstance is that the excavator may know the horizontal location of the service, but may not know the depth, so that there is a need for means for indicating the depth of a service. In other cases, excavation may be being carried out for reasons unrelated to the underground service, and an excavator may be unaware of the presence of the service in the excavation region. In these cases,, the provision of means indicating the presence of the service may act as a warning to the excavator, and so reduce the likelihood of damage to the service, or harm to the excavator, occurring during excavation. It is known, for example in US Patent 3504503 (Allen) to bury in the ground a coloured tape positioned above an underground service to indicate the location of the service. When an excavator is digging to locate the service, it is intended that the tape is torn and brought up with earth so as to indicate the position of the service. The tape is easy to lay because it can be paid out from a reel, but it has the disadvantage that, it may be removed when mixed with soil and may not be seen by the excavator. It is also known, for example in US Patent 3115861 (Allen), to indicate the position of an underground service by depositing in the ground above the service a water insoluble pigment mixed with a filler so as to give a volume of coloured material in the ground. The filler may be an organic substance such as to disintegrate or disappear so as to leave the coloured pigment in the soil. This gives a volume of coloured material, but is less convenient to lay than a tape. It is an object of the present invention at least in preferred embodiments, to provide-a device and method for indicating the presence of an underground service or other underground object which gives a clearer indication of the presence of the underground object r combined with greater ease of installation, than has been present in known arrangements. According to the present invention there is provided a device for indicating the presence of an underground object comprising a carrier and a coloured material carried by the carrier, the carrier being biodegradable to leave the coloured material in the soil, in which the coloured material is a water soluble dye whereby the coloured material dissolves in soil moisture and diffuses into the soil beyond the position of the carrier. Preferably the carrier is in the form of an elongate strip of material. Although the width of the elongate strip may vary for example in dependence upon the width of a service above which the strip is placed, ? 05 it is preferred that the elongate strip has a width of from 100mm to 300mm, and preferably approximately ' 150mm. The elongate strip may have a thickness of from 50 microns to 100 microns. However, in a preferred embodiment, the elongate strip has a thickness of 10 approximately 75 microns. By way of example, the elongate strip may be buried in the ground at a depth of from 100mm to 500mm, and preferably approximately 300mm. The carrier is preferably adapted to degrade within approximately 6 months of burial of the elongate 15 strip in the ground above the service, so as to release the coloured dye into the ground. However, in some arrangements the material may be arranged to degrade more quickly, for example within a few days. 20 Preferably the coloured material is distributed throughout the carrier. In a preferred form the carrier comprises a biodegradable plastics material and conveniently the carrier consists of a non-biodegradable polymer and a biodegradable organic 25 material. Conveniently the non-biodegradable polymer is present in the range 40 to 80 per cent by weight of the device. The biodegradable organic material may be present in the range 5 to 40 per cent by weight of the device. The water soluble dye may be present in the 30 range 1 to 40 per cent by weight of the device. In one particularly preferred form, the o non-biodegradable polymer is ethylene vinyl acetate copolymer. The biodegradable organic material may , 35 conveniently be starch. In a particularly preferred form, the device comprises 50 to 70 per cent by weight of ethylene vinyl acetate copolymer, 10 to 30 per cent by weight of starch, and 10 to 30 per cent by weight of the water soluble dye. Where features of the invention have been described with reference to an indicating device, such features may also be provided in accordance with a method of indicating the presence of an underground object in accordance with the invention. In particular there may be provided in accordance with the invention a method of indicating the presence of an underground object comprising burying in the ground in the vicinity of an underground object a device comprising a biodegradable carrier and a coloured material carried by the carrier, and allowing the carrier to degrade to leave the coloured material in the soil, in which the coloured material dissolves in soil moisture and diffuses into the soil beyond the position of the carrier. The method has particular application where the method includes laying the device in the form of an elongate strip aligned along the length of an elongate underground service and positioned at a higher level than the underground service. A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which is a schematic representation of a device embodying the invention buried in the ground above a service. The figure shows a section of earth 1 in which is buried a service in .the form of a pipe 2. An elongate strip of a plastics material in the form of a tape 3 is buried in the earth 1 above the pipe 2. The tape is positioned in the earth 1 so that it extends along the length of, and substantially vertically above, the pipe 2. The tape 3 contains a coloured dye dispersed throughout the material thereof, which material is a degradable plastics material. The tape 3 has a width of approximately 150mra and a thickness of approximately 75 microns. The tape 3 is buried in the earth 1 at a depth of approximately 300mm beneath the surface 4 of the earth 1. The tape 3 is conveniently laid in its operative position at the time the pipe 2 is first installed. At this time, an excavator will have dug a trench in the earth 1 in which to lay the pipe 2. Once the pipe 2 is installed, the excavator then refills the trench above the pipe 2 to a depth of approximately 300mm below the surface 4 of the earth. The tape 3 is then laid along the length of the trench so that the tape extends above the pipe 2. The remainder of the trench above the tape 3 is then refilled with earth. As previously stated, the tape 3 comprises a degradable plastics material containing a coloured dye. Within about 6 months of burial of the tape 3 in the ground, the plastics material degrades releasing 6-he coloured dye into the ground above the pipe 2. When it is desired to locate the pipe again, for example to carry out repair work, an excavator may have only a rough guide as to the position of the pipe. If excavation is commenced in the region of the pipe, an excavator need only dig up the surface of the earth in the region of the pipe to a depth of approximately 300mm until he locates the coloured dye. Once the dye has been located, the excavator then knows that the pipe lies directly beneath the dye and can continue digging in order to access the pipe. Conveniently the final excavation is carried out carefully by hand to avoid damaging the service. The use of the invention can be merely to indicate the general location of the service, or, more importantly, to indicate a safe depth to which mechanical excavation can take place . The release of the coloured dye into the ground after degradation of the plastics material is achieved by virtue of the coloured dye being a water soluble dye which dissolves in soil moisture and diffuses into the soil beyond the position of the original tape 3 carrying the dye. It is a particular advantage of the present invention that the indicator device formed by the tape 3 can be easily stored and easily laid above the service 2 by paying out the tape, for example, from reel. However, once the tape has degraded in the soil and the dye has dissolved in soil moisture and diffused into the soil beyond the position of the original tape 3, a much clearer indication of the service 2 is provided. The water soluble dye diffuses upwardly and downwardly into the soil, leaving a coloured band. having a significant three dimensional extent which is much more readily detectable than a simple coloured tape. By way of example, the water soluble dye may diffuse upwardly and downwardly to give a total depth of coloured soil of 50 to 100mm. The following example is given to set out one embodiment of the invention. EXAMPLE The following method was used to prepare an elongate strip of plastics material for use as an indicating device. The material contained 20gm. of water soluble yellow dye, 60gm. of ethylene vinyl acetate copolymer (EVA) grade EY907, and 20gm. of maize starch. The EVA copolymer ingredient was fluxed by feeding the commercial granular product into the nip of a 30x15 cm laboratory 2-roll mill with the rolls held at a temperature of about 100 Centigrade, sufficiently hot to flux the polymer but not so hot as to cause sticking to the rolls or thermal decomposition of the dye. When the EVA was running as a smooth band on the rolls the maize starch and the powdered dye were added steadily as the mixing action progressed. On completing the additions the hide of mixture was cut from the rolls, turned through 90 degrees, and returned to the rolls two or three times to ensure uniformity of the blend. Finally the hide was cut from the rolls and cooled. Smooth sheets were then prepared from the hide by pressing it between polished stainless steel plates faced with polyester foil, the thickness of these sheets being fixed by using a steel frame 2mm thick surrounding the material. Pressing was carried out using a 2 minute press cycle in a hydraulic press with electrically heated platens maintained at a temperature of 100 Centigrade. When samples of these pressed sheets were buried in damp soil the presence of micro-organisms in the soil made the plastic composition porous by digesting the starch particles and this, in turn, permitted the water soluble yellow dye to diffuse out of the plastic composition into the surrounding damp soil staining it yellow, an effect clearly visible to the eye within a few days of burying the samples. It is to be appreciated that a number of variations may be made in the material of the carrier, and in the dye which is used. In the example given, EVA was selected because of its compatibility with solid additives and its ease of degradation. Other polymers, such as polyethylene itself or its copolymers and blends with other thermoplastics such as EPDM (Ethylene Propylene Dine Terpolymer) or SBR (Styrene Butadine Rubber) can be used. In choosing the propor¬ tions of the components, it may be found that there is an upper limit to the amount of starch present above which extrusion would be impossible, and this limit may be 70% by volume. The lower limit for the starch to have any effect is about 5% by weight (density 1.3 to 1.5 according to type) and, since the development of porosity is down to the action of the starch, the lower limit for the water soluble dye could be 1% by weight, although the objective is to carry as much as possible. As to the type of starch, there are many different types of starch which may be used. e.g. maize, wheat, barley, oats, potato, rice, sago, and tapioca. One dye which has been found suitable is Aravit 3111807 Tartrazine yellow made by the Williams Division of Morton Thiokol Ltd. Other water soluble dyes can be used provided they are non-toxic and show some degree of retention by soils. A permanent coloured zone will be established in the soil if the chemical nature of the soluble dye is such that it can be adsorbed onto the colloidal ingredients (humus, and colloidal silicates and aluminates) in the soils in the same way that soluble dyes are irreversibly attached to appropriate textile fibres.

Claims: CLAIMS 1. A device for indicating the presence of an underground object comprising a carrier and a coloured material carried by the carrier, the carrier being biodegradable to leave the coloured material in the soil, in which the coloured material is a water soluble dye whereby the coloured material dissolves in soil moisture and diffuses into the soil beyond the position of the carrier. 2. A device according to claim.1 in which the carrier is in the form of an elongate strip of material. 3. A device according to claim 1 in which the coloured material is distributed throughout the carrier. 4. A device according to claim 1 in which the carrier comprises a biodegradable plastics material. 5. A device according to claim 4 in which the carrier consists of a non-biodegradable polymer and a biodegradable organic material. 6. A device according to claim 5 in which the non- biodegradable polymer is present in the range 40 to 80 per cent by weight of the device. 7. A device according to claim 5 in which the biodegradable organic material is present in the range 5 to 40 per cent by weight of the device. 8. A device according to claim 5 in which the water soluble dye is present in the range 1 to 40 per cent by weight of the device. 9. A device according to claim 5 in which the non- biodegradable polymer is ethylene vinyl acetate copolymer. 10. A device according to claim 5 in which the biodegradable organic material is starch. 11. A device according to claim 1 in which the device comprises 50 to 70 per cent by weight of ethylene vinyl acetate copolymer, 10 to 30 per cent by weight of starch, and 10 to 30 per cent by weight of the water soluble dye. 12. A method of indicating the presence of an underground object comprising burying in the ground in the vicinity of an underground object a device comprising a biodegradable carrier and a coloured material carried by the carrier, and allowing the carrier to degrade to leave the coloured material in the soil, in which the coloured material dissolves in soil moisture and diffuses into the soil beyond the position of the carrier. 13. A method according to claim 12 including laying the device in the form of an elongate strip aligned along the length of an elongate underground service and positioned at a higher level than the underground service.

Inventors: HARVEY CHRISTOPHER JAMES, MORGAN DEREK MICHAEL, HARVEY, CHRISTOPHER, JAMES, MORGAN, DEREK, MICHAEL
Applicants: HARVEY CHRISTOPHER JAMES, MORGAN DEREK MICHAEL, HARVEY, CHRISTOPHER, JAMES, MORGAN, DEREK, MICHAEL
Application year: 1991
Main classification: G01V9
IPC codes: C08J5, F16L1, G01M3, H02G9