GB2532087A

GB2532087A - Method of installing services under footways

Info

Publication number: GB2532087A
Application number: GB1419997.0A
Authority: GB
Inventors: Henry Patrick
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-11-10
Filing date: 2014-11-10
Publication date: 2016-05-11
Anticipated expiration: 2034-11-10
Also published as: GB201419997D0; GB2532087B

Abstract

A method is disclosed of installing services 3 under a footway 1 which comprises the steps of: a) excavating a trench 2 having a width of 70 to 150mm and a depth of 250mm or greater below a surface level of the footway; b) installing the services in a base 20 of the trench; c) backfilling the trench with foamed concrete 6 to no less than 30mm below the surface level of the footway ; d) curing the foamed concrete; e) installing a top layer 5 on top of the foamed concrete to reinstate the trench to at least the surface level 7 of the footway.

Description

Method of installing services under footways The present disclosure relates to a method of installing services, for example ducting, under footways, in particular bituminous footways sometimes referred to as flexible footways.

Background

It is known to locate services under the highway. For example, utilities such as electricity, gas and water may be located in pipes laid beneath the surface level of the highway. The pipes may be laid at the time of first installing the highway or may be laid under pre-existing highways by excavating a trench, laying the services and then reinstating the trench back to the surface level of the highway. In general, for utilities such as electricity, gas and water the diameter of the pipes is relatively large and the pipes may be laid under the carriageway portion of the highway that receives vehicular traffic, with smaller services to households crossing footways and entering the dwellings.

In recent years there has been a desire to install other services under the highway. One example is telecoms services, in particular the laying of optical fibre services to provide, for example, cable television, telephone and internet services. This can lead to significant installation costs since multiple trenches must be excavated to reach each dwelling place. In addition, prior-used excavation techniques have been found by the present applicant to be poorly suited to installing this type of telecoms services. For example, prior trenching techniques result in the formation of wide trenches having a width in excess of 200 mm. These are undesirable for use in a footway due to the amount of disruption of the footway surface and the cost involved in reinstating said wide trench. In addition, the size of the wide trenches can cause significant disruption to the foot traffic on the highway. The wide trenches also incur additional cost in extending trim lines to where trim-lines for the reinstatement edges are within 150 mm of an edge, kerb, ironwork or other reinstatements. An alternative solution has in the past been tried which is known as micro trenching which involves the cutting of a very narrow trench (approximately 10 to 60 mm) by means of a -2 -rotating diamond-tipped saw or rotary toothed spinner. However, micro trenching has experienced a number of drawbacks, including the problems that it is difficult to form a micro trench of a sufficient depth to install the services at the correct depth according to National Joint Utilities Group (NJUG) guidelines. Many local and highways authorities have expressed a number of reservations regarding the practice of micro trenching, primarily around consistency of deployment, potential liabilities and integrity of the highway or footway.

The footways of the highway may be of a number of types. Typically, the footway will be a bituminous footway having a top layer of asphalt or other bituminous material. Other options include modular paved footways, where the top layer of the footway is formed from paving stones, bricks or a similar product, and concrete-topped footpaths.

There therefore remains a need to provide a cost-efficient method of installing services, such as telecoms services, to individual dwelling places if the take-up of such services is to be increased geographically. This is especially important in the field of broadband provision as more households connect multiple devices and utilise technology demanding greater speeds.

Summary of the Disclosure

According to the present disclosure there is provided a method of installing services under a footway, comprising the steps of: a) excavating a trench having a width of 70 to 150mm and a depth of 250mm or greater below a surface level of the footway; b) installing the services in a base of the trench; c) back-filling the trench with foamed concrete to no less than 30mm below the surface level of the footway; d) curing the foamed concrete; e) installing a top layer on top of the foamed concrete to reinstate the trench to at least the surface level of the footway.

Advantageously, by using a narrow trench having a width of 70 to 150mm a significant cost saving is made compared to using a wider trench. Savings are made in the time to excavate the trench, the cost of the backfill and reinstatement -3 -materials and also the cost of disposal of the resulting spoil. In addition, the narrow trench of the present disclosure is suitable for use in the footway of the highway. Advantageously, the trench may be formed using smaller equipment such as mini-excavators and hand-operated machinery -that reduces the disruption to foot traffic on the footway. In addition, the trenching method of the present disclosure has distinct advantages over micro-trenching since the trench can be formed to a depth of at least 250mm allowing for correct depth of placement of the services. In addition, the present method conforms in its entirety to the New Roads and Street Works Act 1991 Specification for the Reinstatement of Openings in Highways Third Edition Code of Practice for England Approved by the Secretary of State under Section 71 of the New Roads and Street Works Act 1991. This allays the fears and concerns of local and highway authorities.

The present applicant has found, contrary to accepted wisdom in the industry, that the use of foamed concrete to back-fill a narrow trench in the footway is advantageous and leads to cost savings. One advantage of the use of foamed concrete is that it is self-compacting. This avoids the problems that ensue through traditional methods of compacting aggregate with a vibrotamper. It is known that foamed concrete requires a curing period (up to 24 hours) before it can be reinstated and it has also been standard in the industry for foamed concrete to be pre-mixed off-site and delivered in large quantities using a large delivery vehicle that dispenses the foamed concrete directly into an open trench. Both of these factors have been a prejudice against using foamed concrete in a narrow trench located in the footway. First, the curing period would suggest that the installation time and cost would be increased compared to using an alternative material. Second, the known delivery technique using a traditional concrete mixer cannot discharge foamed concrete accurately into a narrow trench without the concrete overspilling the edges of the trench. Third, it would be anticipated that access of the large delivery vehicle to the footway location (which may be quite distant from the carriageway) would not always be possible. The present applicant has solved these problems of using foamed concrete in a narrow trench by the use of various techniques as will be described further below. -4 -

The foamed concretes are cement-bound materials that are flowable in nature and should not require compaction when placed. They conform to Clause 1043 of the Specification for Highway Works and are deemed to be approved for use as Alternative Reinstatement Materials in accordance with Appendix 9 of the SROH. They may range in strength with a crushing strength at 28 days ranging from C1.5/2 to C9/12 Maximum.

With the present disclosure, in step a) the excavated trench may have a width of 70 to 100mm, preferably about 70mm. A narrow trench of around 70mm has been found to be achieve a good balance of reducing the amount of spoil produced, permitting the required depth of trench to be produced and allowing back-filling with foamed concrete.

The present disclosure finds particular advantage when utilised where the footway is a bituminous footway and step e) comprises installing a bituminous layer on top of the foamed concrete to reinstate the trench to at least the surface level of the bituminous footway. By using the foamed concrete to back-fill the trench a thinner bituminous layer can be utilised with resultant cost savings. In step e) the bituminous layer may have a depth of 30 to 40mm, preferably 30 to 35mm, more preferably about 30mm. This compares favourably to traditional bituminous layers that are normally greater than or equal to 60mm in thickness.

In step b) the services may comprise ducting. The ducting may contain one or more services, for example, telecoms services. The ducting may be microducting, preferably a bundle of microducts with each microduct preferably having an outer diameter of from 8 to 16mm. Each microduct may contain a fibre optic cable. The bundle of microducts may be contained within an outer duct.

In step a) firstly two parallel cuts may be formed in the footway, and subsequently the trench may be excavated. The two parallel cuts may be formed using a double-cut floorsaw. For example the floorsaw may be provided with diamond-tipped rotating cutting members and be sized to form cuts to a width of up to 100mm.

Subsequently, the trench may be excavated using an excavator equipped with a bucket having a width of 50 to 70mm. By using a specialised bucket of narrow width a narrow trench may be formed. Preferably spoil is dragged along -5 -the length of the trench rather than be vertically lifted out of the trench to avoid lifting and damaging the surface of the footway alongside the parallel cuts.

Prior to step c) detectable marker tape may be installed with the services in the base of the trench. The detectable marker tape assists in locating the position of the services after reinstatement of the footway, for example by using a suitably-configured detector. In one example the detectable marker tape comprises a copper wire.

Optionally, a sand layer may be laid over the installed ducting or the ducting may be pegged to the base of the trench before back-filling takes place.

o In step c) the foamed concrete may be back-filled from a gravity-fed hopper. The gravity-fed hopper may be mounted to a vehicle or hand-drawn. Advantageously, by using gravity feed rather than pump-dispensing of the foamed concrete the product may be accurately discharged into the open narrow trench while reducing or eliminating overspill.

In step d) during curing of the foamed concrete an opening of the trench in the footway may be covered by a plurality of trench boards. Each trench board may comprise a lateral member which is configured to have a width greater than the width of the trench and a projecting member which extends perpendicularly from the lateral member and is configured to be received in the opening of the trench. Advantageously, the use of such trench boards removes the need for pedestrian barriers to be installed along the length of the trench during the curing period. As such, disruption of foot traffic during this stage is minimised and the danger of a pedestrian stepping into an open trench is removed. Curing of the foamed concrete may be increased by the use of appropriate admixtures.

In step e) material for forming the top layer may be fed into the trench using a trench box. The trench box is preferably hand-drawn. The trench box comprise a hopper for the top layer material, e.g. asphalt, and a funnel of a suitable width for the narrow trench. Preferably the trench box allows for the top layer material to be compacted as it is filled into the trench.

Brief Description of the Drawings -6 -

An example of the present disclosure will now be described in more detail, for exemplary purposes only, with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-sectional view of services installed in a trench according to the present disclosure after reinstatement; Figure 2 is a picture illustrating excavation of a trench of the type shown in Figure 1; Figure 3 is a picture of the use of trench boards for covering a trench of the type shown in Figure 1 during installation; Figure 4 is a schematic cross-sectional view of Figure 3; Figure 5 is a picture illustrating installation of a top layer in the trench; and Figure 6 is a picture of a rockwheel/topcutter.

Detailed Description

In the following description the present disclosure will be illustrated as applied to a footway having a bituminous top layer. However, the method may also be applied to footways with other types of top layer, for example, concrete and modular paved layers.

Figure 1 illustrates services 3 installed at the bottom of a trench 2 made according to the present disclosure after reinstatement of the trench 2. The trench 2 is formed in a footway 1 of a highway that normally receives foot traffic. A surface level of the footway 1 is shown by reference numeral 7.

The finished and reinstated trench 2 has a width w of 70 to 150mm, preferably 70 to 100mm, more preferably about 70mm. The trench 2 had side walls 21 that are generally vertical. The services 3 are located at a base 20 of the trench 2 and comprise a bundle of ducting. The ducting may be microducts and may have various sizes. In the illustrated example microducts 31 have an outer diameter of 8mm and microducts 32 have an outer diameter of 16mm. The microducts 31, 32 may carry optical fibre. The depth d of the trench 2 (measured to the top of the installed services 3) below the surface level 7 is greater than or equal to 250mm as shown in Figure 1.

The reinstated trench 2 is back-filled with foamed concrete 6 up to a depth dt below the surface level 7. The remainder of the trench 2 is filled with a top layer 5 having a depth of at least dt so that the footway 1 is reinstated back to a level finish. According to the present disclosure the depth dt of the top layer is at least 30mm and is preferably no more than 60mm.

Installation of the services 3 involves the following stages: a) excavating the trench 2; b) installing the services 3 in the base 20 of the trench 2; c) back-filling the trench 2 with foamed concrete 6 to no less than 30mm below the surface level of the footway; d) curing the foamed concrete 6; e) installing the top layer 5 on top of the foamed concrete 6.

In stage a) excavating the trench 2 involves first cutting through the pre-existing bituminous layer of the footway 1. In one example, a double-cut floorsaw is used wherein the diamond-tipped cutting blades are set at the required spacing of 70 to 150mm. To improve production a rockwheel/topcutter may be deployed. This is a hydraulically driven wheel with picks, see the example of Figure 6.

Next, the trench 2 is excavated and the resulting spoil is removed using a mini-excavator equipped with a narrow bucket of width 50 to 150mm as shown in Figure 2. Once a depth of at least 250mm plus the depth required for the services 3 is reached excavation can be stopped.

In stage b) the services 3 are installed. Preferably the microducts 31, 32 are fed from rotating drums held on a cable trolley which allows for long lengths of the microducts 31, 32 to be laid in one operation. Optionally a sand layer may be applied to the services 3 or pegging used to ensure that the services 3 remain in position during back-filling of the trench 2.

Optionally, detectable marker tape containing, for example a copper wire, may be installed with the services 3 in the base 20 of the trench 2.

In stage c) foamed concrete 6 is filled into the trench 2 on top of the services 3. The foamed concrete 6 may, for example, conform to Clause 1043 of -8 -the Specification for Highway Works. They may range in strength with a crushing strength at 28 days ranging from C1.5/2 to C9/12 Maximum. The foamed concrete 6 is preferably held and discharged from a relatively small gravity-fed hopper. The gravity-fed hopper may be mounted to a vehicle or hand-drawn. The foamed concrete 6 is filled to the depth dt below the surface level 7 and may be levelled with an adapted squeegee to ensure the correct depth before being left to cure.

In the curing stage d) the upper opening of the trench 2 is preferably covered by a plurality of trench boards 9 as shown in Figures 3 and 4. Each trench board 9 comprises a lateral member 13 which is configured to have a width greater than the width of the trench 2 and a projecting member 14 which extends perpendicularly from the lateral member 13 and is configured to be received in the opening of the trench 2 as shown in Figure 4. The foamed concrete is then left to cure for up to 24 hours.

In step e) the bituminous material for forming the top layer 5 is fed into the trench 2 using a trench box as shown in Figure 5. The trench box is preferably hand-drawn. The trench box comprise a hopper for the top layer material, e.g. asphalt, and a funnel of a suitable width for the narrow trench. Preferably the trench box allows for the top layer material to be compacted as it is filled into the trench. The bituminous layer will have a depth of at least di so that the surface level 7 of the footway 1 is re-established. The depth of the top layer 5 may be 30 to 60mm, preferably 30 to 45mm, more preferably about 30mm.

Of course it will be appreciated that the stages of the present method lend themselves to being carried out in a parallel manner on a single installation site.

For instance, while one stretch (e.g. of one to several hundred metres of length of trench 2) may be being left to allow the foamed concrete 6 to cure the next stretch may be being excavated and the previous stretch may be having the top layer 5 installed. -9 -

Claims

Claims: 1. A method of installing services under a footway, comprising the steps of: a) excavating a trench having a width of 70 to 150mm and a depth of 250mm or greater below a surface level of the footway; b) installing the services in a base of the trench; c) back-filling the trench with foamed concrete to no less than 30mm below the surface level of the footway; d) curing the foamed concrete; o e) installing a top layer on top of the foamed concrete to reinstate the trench to at least the surface level of the footway.
2. The method of claim 1, wherein the footway is a bituminous footway and step e) comprises installing a bituminous layer on top of the foamed concrete to reinstate the trench to at least the surface level of the bituminous footway.
3. The method of claim 2, wherein in step e) the bituminous layer has a depth of 30 to 40mm, preferably 30 to 35mm, more preferably about 30mm.
4. The method of any preceding claim, wherein in step a) the excavated trench has a width of 70 to 100mm, preferably about 70mm.
5. The method of any preceding claim, wherein in step b) the services comprises ducting.
6. The method of claim 5, wherein the ducting is microducting, preferably a bundle of microducts with each microduct preferably having an outer diameter of from 8 to 16mm.
7. The method of any preceding claim, wherein in step a) firstly two parallel cuts are formed in the footway, and subsequently the trench is excavated.

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8. The method of claim 7, wherein the two parallel cuts are formed using a double-cut floorsaw.
9. The method of any preceding claim, wherein the trench is excavated using 5 an excavator equipped with a bucket having a width of 50 to 70mm.
10. The method of any preceding claim, wherein prior to step c) detectable marker tape is installed with the services in the base of the trench.
11. The method of any preceding claim, wherein in step c) the foamed concrete is back-filled from a gravity-fed hopper.
12. The method of any preceding claim, wherein in step d) during curing of the foamed concrete an opening of the trench in the footway is covered by a plurality of trench boards.
13. The method of claim 12, wherein each trench board comprises a lateral member which is configured to have a width greater than the width of the trench and a projecting member which extends perpendicularly from the lateral member and is configured to be received in the opening of the trench.
14. The method of any preceding claim, wherein in step e) material for forming the top layer is fed into the trench using a trench box.