BACKGROUND OF THE INVENTION: Whilst the open cut technique provides the highly desirable possibility, during back- filling, of introducing into the back-filling material a warning or caution means, such as one or more synthetic plastics, caution-printed and/or colour marked ribbons above the installed utility line, so that subsequent contractors repairing the line, or installing a different utility line, do not inadvertently damage a utility line, substantial ancillary costs are involved in disposal of extracted spoil, purchasing of back-filling material, and re-surfacing and/or relaying of paving, whilst furthermore there is a limit to the depth of open cut trench that can be economically excavated.

Such ancillary costs are largely avoided by the use of the directional drilling technique whereby only a relatively small bore hole with minimal spoil is produced, virtually at any depth. but it is not possible to introduce into the ground cautionary ribbons etc. to give early warning of the presence of a service line to subsequent contractors.

Another disadvantage with directional drilling for installing a mains electric cable for instance, is the conventional procedure of lining the drilled bore hole with a polyethylene sleeve

or pipe. along which pipe the power cable is then threaded, because, unlike the open-cut technique, the pipe restricts the dissipation heat, resulting in a disadvantageous de-rating of the power cable.

OBJECT OF THE INVENTION A basic object of the present invention is the provision of an improved method of installing a utility line, such as a power cable, and to apparatus for carrying out such method.

SUMMARY OF THE INVENTION A method of installing an underground utility line such as a relatively small diameter power cable into a relatively large diameter bore-hole usually extending horizontally or generally so, comprising the steps of:- (i) hauling the utility line along the bore hole so as to install the utility line along the bottom or floor of the bore hole; (ii) simultaneously or subsequent hauling at least an outer sleeve of a warning/protective line in a pre-activated form along the bore hole and in an orientation whereby the warning/protective line is maintained above the utility line; (iii) inserting into the outer sleeve either before or after installation of the outer sleeve into the bore hole a dual element line comprising an inflatable, elongate sock of synthetic plastics material, which in turn surrounds the grout pipe; (iv) anchoring the leading end of the utility line and the warning/protective line at a terminal end of the bore hole;

(v) retracting the outer sleeve from the leading or start end of the bore hole so as to expose the sock along the bore hole; (vi) inflating the sock with pressurised air: and (vii) introducing grout from the grout pipe into the sock starting at or adjacent the terminal end of the bore hole and working towards the lead or start end of the bore hole, whilst simultaneously progressively withdrawing the grout pipe from the leading end of the bore hole, whereby the pressurised air is progressively replaced by grout, and the grout-filled sock is then effective as a waming/protective upper covering to the utility line.

It follows that if the bore hole is of say 150-200 mm diameter, and if the utility line is an electrical cable of 50-100 mm diameter, the cable extends along the bottom of the bore hole and consequently the waming/protective line, firstly upon sock inflation and secondly upon subsequent sock filling with pressurised grout, is expanded into the remaining area of the bore hole, providing not only a hardened waming/protective cover extending above the cable for the length of the bore hole, but also protective side cheeks extending to each side of the cable, whilst, in addition, a printed warning on, and/or colouration of, the sock exterior provides further visual warning as to the presence of the utility line.

Preferably, the bore hole is initially produced by directional drilling to a desired length e. g. 100-200 m, depth e. g. 2 m, and diameter e. g. 160 mm, from a launch pit at a leading end of the bore hole to a recovery pit at the terminal end of the bore hole, with drilling preferably being followed by back reaming to improve the profile and gauge of the bore hole.

The warning/protective line in its pre-activated form is pre-prepared as a triple element line and conveyed to site e. g. as a coil. In detail, a grout pipe e. g. of rubber, typically of 32 mm,

may be passed from a grout pipe reel to and through a sock former whereby firstly the sock, typically of 150 mm diameter, is applied to the exterior of the grout pipe and thereafter the sock and grout pipe composite is passed into an external sleeve e. g. of synthetic plastic material. typically polyethylene, typically of 75 mm. Preferably, the sock is of 500 gauge polythene, such that the latter may be folded, in concertina fashion, into a relatively small length. e. g. 1 m, and to be drawn out, e. g. to 50 m, as the grout pipe progresses through the former. Alternatively, the outer sleeve of the warning/protective line may be installed in the bore hole, above the utility line, with the sock and grout pipe introduced, as a dual element line into the outer sleeve and advanced along the sleeve by halving, to form the triple element warning/protective line.

Installation of the dual element line along the outer sleeve may be assisted by applying pressurised air to the interior of the outer sleeve, to cause inflation. or diametrical expansion, of the outer sleeve.

Preferably, both back reaming and insertion of the utility line and waming/protective line are effected simultaneously with a puller attached to the reamer, to which puller are attached both the utility line and waming/protective line, preferably via individual swivel eyes.

According to another aspect of the invention, there is provided apparatus for use in carrying out the above defined method in the form of a dual element warning/protective line comprising: (i) an inner grout pipe; and (ii) an inflatable sock of synthetic plates material surrounding the grout pipe and extending along its length.

According to another aspect of the invention, there is provided apparatus for use in carrying out the above defined method in the form of a tripe element waming/protective line

comprising: (i) an inner grout pipe; and (ii) an inflatable sock of synthetic plates material surrounding the grout pipe and extending along its length and an external sleeve surrounding the inflatable sock.

In order to achieve inflation of the sock e. g. to 2/3 bar pressure, the latter is connectable to an air inflation jig, whilst the grout pipe is connectable to grout pumping apparatus.

The method and apparatus of the invention will now be described in greater detail, by way of examples, with reference to the accompanying drawings, in which: Figures 1A to 1D illustrates four successive steps involved in carrying out the method of invention: Figure 1E is a section through a finished installed cable and warning/protective covering; Figure 2 indicates diagrammatically a technique for applying the sock to the grout pipe and the thus formed composite into the surrounding pipe; and Figure 3 indicates a suitable air inflation jig.

In the drawings, a bore hole 1, e. g. of 160 mm diameter has been produced by directional drilling from a launch pit (not shown) at the leading end of the bore hole 1, to a terminal end at a recovery pit (not shown). After drilling, a reamer 2 with a leading towing cable 3 and a trailing towing cable 4, is passed along the bore hole 1 as indicated in Figure 1A. To the end of the trailing towing cable 4 is attached a second reamer 5 provided at its rear end with a swivel eye 6 to which is attached a puller 7, of 150 mm diameter, for a utility line in the form of a 50- 75 mm electrical cable 8 located at the bottom of the bore hole 1 (as illustrated in Figure 1E) and a warning/protection line 9 located above the cable 8, via interposed fittings 10 and 11 respectively, as illustrated in Figure 1B.

The warning/protective line 9 is a triple element comprising a pre-assembled innermost grout pipe 12 of rubber, typically of 45 mm external diameter, which is externally surrounded by an inflatible, elongate sock 13. e. g. of 500 gauge polythene, typically of 150 mm diameter. which is surrounded by an external sleeve 14, e. g. of polyethylene, typically of 75 mm. the line 9 being supplied to site in reel form.

Upon the puller 7 reaching the recovery pit, the fitting 11 is anchored. so that retraction of the sleeve 14 may commence at the launch pit, to expose the sock 13. A supply of compressed air, typically at 2-3 bar, is then introduced into the sock from the launch pit to inflate the sock to fill the remainder of the bore hole 1. Then, as illustrated in Figure 1C, pumping of grout along the grout pipe 12 from grout pumping apparatus (not shown) located in, or adjacent the launch pit is commenced, with grout firstly being discharged from apertures 15 in its fitting 10 at the leading end of the bore hole 1, and with the grout pipe 12 gradually being retracted as grouting progresses, until the situation illustrated in Figures 1D and 1E is achieved.

Figure 2 illustrates a sock fitting apparatus 16, showing how the sock 13 may be applied to the grout pipe 12. In detail,, the rubber grout pipe 12 is pulled from a storage reel 17 and is passed through a 90 mm polyethylene assembly pipe 18 onto which the sock 13 is deposited, in concertina fashion, from a sock former 19. Some 50 m of sock 13 may be stored on a 1.2 m assembly pipe 18, the grout pipe 12 gradually pulling the sock from the assembly pipe 18 until 50 m of composite line 9 has been coiled onto a reel 20, which is then ready for transport to site.

Figure 3 illustrates an air inflation jig 21. In detail, a 160 mm pipe length 22 is fitted over the sock 13 with a trailing end 23 of the sock 13 secured by two steel straps 24 to a branch 25 of a jig 26, the branch 25 having a compressed air inlet line 27 with a valve 28, a pressure gauge 29, three 125 mm flange rings 30, with a gasket 31, a rubber"O"-ring seal 33. and a frame 33 with securing threaded rods 34 and nuts/washers.