U Mole aids challenging gas pipe replacement with multiple systems
U Mole (a division of Vp plc) recently provided two products from its hire range to assist on a challenging Dual Carriageway for client Manterfield Drilling Ltd which required the replacement of a 25 mm diameter PE gas main with a new 90 mm diameter PE supply as part of upgrading works at Sandall Treatment Works, one of Yorkshire Water’s sewage treatment plants. The two systems were a KOBUS Cable Puller and a PB30 cable-based pipe bursting system.
The existing gas main ran beneath a section of the A630 Wheatley Hall Road dual carriageway near Doncaster. As well as upsizing the existing 25 mm diameter PE supply to 90 mm diameter PE, the new supply main had to be tee’d off a nearby existing 16 in diameter gas main. The dual carriageway crossing length was some 18m. Concerns within the local authority and highways for the maintenance of the existing road condition mean the neither HDD techniques nor the use of a 110 mm diameter impact moling technique could be considered for the direct installation of the new gas supply. Indeed, the contractor did attempt to use a small diameter service mole to create a bore for the PB30 cable to be installed into for subsequent upsizing to 110 mm diameter rather than utilise the KOBUS pipe pulling system. However, during the course of these works the moled crossing had to be aborted due to extremely compact ground conditions beneath the road way.
The fact that the existing service ran beneath a dual carriageway was challenging enough in itself however on further investigation of the site it was found that other obstacles increased the site challenges even further. The 25 mm diameter service was found to change level substantially part of the way through its route. Not only this the pipe changed from being initially PEX material at one side to being PEA material at the other. This change of material and a joint would appear to indicate that at some point in its life a possible repair had needed to be undertaken at some time. In addition to this, the old single carriageway road surface that used to run across the site was found to still exist under the new dual carriageway surface.
There were also access restrictions imposed on works at the site. These meant that any excavations in the carriageway could only be opened only 9.30 a.m. with guarantee to that the excavation would be reinstated by 3.30 p.m. on each day it was open. With these restrictions and no potential for utilising HDD or moling for the job, Manterfield looked at utilising the KOBUS system to initially pull out the old service and at the same time pull in the 19 mm diameter compacted wire rope that was used with a HammerHead PB30 cable-based pipe bursting system. Once this was installed the plan was to use the PB 30 to upsize the bore from 25 mm diameter to 110 mm diameter to enable the new 90 mm diameter PE service to be installed along the same route as the old supply.
To extract the existing gas service pipe a KOBUS consumable kit was utilised with 20 m of pulling cable and a burst head. Initially the cable was inserted into the old pipe with KOBITE being injected into the annular space to lock the cable in place. Once the Kobite had set (a process which took over 1 hour due to cold weather conditions) the pipe and cable become one. The KOBUS puller was then utilised to pull out the PE service and install the compact PB30 cable.
After just 3 m of the pull-back operation the process stalled. Tension was maintained for 10 minutes with only very slow movement. The PE pipe at the KOBUS puller end of the arrangement yielded (at a joint it was later discovered) but the wire held and it was decided to continue with the pull. Over a timeframe of about 1 hour the cable was retrieved until around 13 m into the pull when the unit stalled again. It was decided to slowly increase the tonnage on the Kobus system in a final effort to get rope extraction completed and the PB30 rope in place. Another 2 to 2.5 m of pull was achieved but then the rope failed. At this point the PB30 cable was some ¾ of the way through the route. The failure was down to exceptionally compact ground and the old carriageway cover. Under these circumstances the KOBUS cable was simply not substantial enough to take the high tonnage required during the pull.
To recover the project, it was decided to dig down on the point of the break to attempt to get to the PB30 cable so that ¾ of the job could be completed. Within the time restrictions for open cut access to the carriageway, the end of the cable was located and the excavation backfilled to allow traffic flow. The next day the first lane of the carriageway was closed off and re-excavated back to the PB30 cable. A 6 in diameter PVC duct was installed and the PB30 cable pulled through to the grass verge beyond the kerb. The lane was then backfilled and reinstated to ensure it could be reopened within the access window allowed by the local council.
Once the PVC duct was in place the PB30 was positioned into its pull-in/receive pit and the upsize operation was commenced. With the new PE pipe connected to the cable behind the expansion head the upsize commenced around 11.30 a.m. Progress was slow and steady with the PB30 running close to its maximum pullback tonnage for most of the upsize run. This was a further indication of just how compacted the surrounding ground was. Half way through the pull the PB30 unit suffered a hose failure, but due to U Mole’s efficient back-up and support service this was repaired in a very short time frame and the machine was up and running again within 1 hour. By 2.00 p.m. the work was completed and the new pipe 90 mm diameter service pipe was installed. The carriage way was fully reopened within the council’s stipulated time and the client ecstatic to have installed the new 90 mm diameter pipe along the line of the old 25 mm diameter PE pipe within the client’s tight deadline.
U Mole is the direct factory UK and Ireland distributor for Earth Tool equipment offering the company’s full range of products for trenchless installation and pipeline replacement. This range includes impact moles (earth piercing tools), pipe ramming hammers, twin capstan winches, static rod pipe bursting systems and the portable cable-based, hydraulic pipe burster range.
U Mole also supplies a full and extensive range of trenchless and limited dig equipment including: Suction/vacuum excavation systems (including MTS systems alongside Vac-Tron systems) and surface coring equipment for the ‘Keyhole’ excavation of utilities and services with minimum disruption to the local area and minimum damage to the buried service. Other trenchless related equipment available includes the market leading Robbins SBU equipment, Pipe to Site coiled pipe trailer range, pipe fusion systems, Reed Tools and a complete range of accessories such as Cobra flexible rodding, towing heads, cable socks, pipe pigs, swivels, breakaway connectors etc.