U Mole (a division of Vp plc) recently providedtwo products from its hire range to assist on a challenging Dual Carriageway forclient Manterfield Drilling Ltd., which required the replacement of a 25-mm diameter PEgas main with a new 90-mm diameter PE supply as part of upgrading works at SandallTreatment Works, one of Yorkshire Water’s sewage treatment plants. The twosystems were a KOBUS Cable Puller and a PB30 cable-based pipe bursting system.
The existing gas main ran beneath a section ofthe A630 Wheatley Hall Road dual carriageway near Doncaster. As well as upsizingthe existing PE supply, the new supply main had to be tee’d off a nearby existing16-in. diameter gas main. The dual carriageway crossing length was some 18 m.
Concerns within the local authority andhighways for the maintenance of the existing road condition mean the neitherHDD techniques nor the use of a 110-mm diameter impact moling technique couldbe considered for the direct installation of the new gas supply.
Indeed, the contractor did attempt to use asmall diameter service mole to create a bore for the PB30 cable to be installedinto for subsequent upsizing to 110-mm diameter rather than utilize the KOBUSpipe pulling system. However, during the course of these works the moledcrossing had to be aborted due to extremely compact ground conditions beneaththe road way.
The fact that the existing service ran beneatha dual carriageway was challenging enough in itself however on furtherinvestigation of the site it was found that other obstacles increased the sitechallenges even further.
The 25-mm diameter service was found to changelevel substantially part of the way through its route. Not only this, the pipechanged from being initially PEX material at one side to being PEA material atthe other. This change of material and a joint would appear to indicate that atsome point in its life a possible repair had needed to be undertaken at sometime. In addition to this, the old single carriageway road surface that used torun across the site was found to still exist under the new dual carriagewaysurface.
There were also access restrictions imposed onworks at the site. These meant that any excavations in the carriageway couldonly be opened only 9:30 a.m. with guarantee to that the excavation would be reinstatedby 3:30 p.m. on each day it was open.
With these restrictions and no potential forutilizing HDD or moling for the job, Manterfield looked at utilizing the KOBUSsystem to initially pull out the old service and at the same time pull in the19-mm diameter compacted wire rope that was used with a HammerHead PB30 cable-basedpipe bursting system. Once thiswas installe, the plan was to use the PB 30 to upsize the bore from 25-mm diameterto 110-mm diameter to enable the new 90-mm diameter PE service to be installedalong the same route as the old supply.
To extract the existing gas service pipe a KOBUSconsumable kit was utilized with 20 m of pulling cable and a burst head. Initiallythe cable was inserted into the old pipe with KOBITE being injected into theannular space to lock the cable in place. Once the Kobite had set (a process thattook more than one hour due to cold weather conditions) the pipe and cablebecome one. The KOBUS puller was then utilized to pull out the PE service andinstall the compact PB30 cable.
After just 3 m of the pullback operation, theprocess stalled. Tension was maintained for 10 minutes with only very slowmovement. The PE pipe at the KOBUS puller end of the arrangement yielded (at ajoint it was later discovered) but the wire held and it was decided to continuewith the pull. Over a timeframe of about one hour, the cable was retrieveduntil around 13 m into the pull when the unit stalled again. It was decided toslowly increase the tonnage on the Kobus system in a final effort to get rope extractioncompleted and the PB30 rope in place. Another 2 to 2.5 m of pull was achievedbut then the rope failed. At this point the PB30 cable was some three-quartersof the way through the route. The failure was down to exceptionally compactground and the old carriageway cover. Under these circumstances the KOBUS cablewas simply not substantial enough to take the high tonnage required during thepull.
To recover the project, it was decided to digdown on the point of the break to attempt to get to the PB30 cable so that three-quartersof the job could be completed. Within the time restrictions for open-cut accessto the carriageway, the end of the cable was located and the excavation backfilledto allow traffic flow.
The next day the first lane of the carriagewaywas closed off and re-excavated back to the PB30 cable. A 6-in diameter PVCduct was installed and the PB30 cable pulled through to the grass verge beyondthe curb. The lane was then backfilled and reinstated to ensure it could bereopened within the access window allowed by the local council.
Once the PVC duct was in place the PB30 waspositioned 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 theupsize commenced around 11:30 a.m. Progress was slow and steady with the PB30running close to its maximum pullback tonnage for most of the upsize run. Thiswas a further indication of just how compacted the surrounding ground was. Halfway through the pull the PB30 unit suffered a hose failure, but due to U Mole’sefficient back-up and supportservice this was repaired in a very short time frame and the machine was up andrunning again within one hour. By 2:00 p.m. the work was completed and the newpipe 90-mm diameter service pipe was installed.
The carriage way was fully reopened within thecouncil’s stipulated time and the client ecstatic to have installed the new 90-mmdiameter pipe along the line of the old 25-mm diameter PE pipe within theclient’s tight deadline.
U Mole is the direct factory United Kingdom andIreland distributor for Earth Tool equipment offering the company’s full rangeof products for trenchless installation and pipeline replacement. This rangeincludes impact moles (earth piercing tools), pipe ramming hammers, twincapstan winches, static rod pipe bursting systems and the portable cable-based,hydraulic pipe burster range.
U Mole also supplies a full and extensive rangeof trenchless and limited dig equipment including: Suction/vacuum excavationsystems (including MTS systems alongside Vac-Tron systems) and surface coringequipment for the ‘Keyhole’ excavation of utilities and services with minimumdisruption to the local area and minimum damage to the buried service. Othertrenchless related equipment available includes the market leading Robbins SBUequipment, Pipe to Site coiled pipe trailer range, pipe fusion systems, ReedTools and a complete range of accessories such as Cobra flexible rodding,towing heads, cable socks, pipe pigs, swivels, breakawayconnectors etc.
This article was submitted by U Mole, Cambs,United Kingdom.