U Mole trains utility operatives on site

Cambridgeshire-based U Mole, a division of VP, recently provided the equipment and training for an Essex & Suffolk Water (E&SW) pipe replacement project beneath Mill Road, Cobham, Great Yarmouth. The project marked the first time that such pipe bursting work had been undertaken directly by water company employees, as opposed to the company¡¯s usual main contractor.

E&SW decided to use its own direct labour for the operation to give its team an insight into the variety of different work methods currently available in the pipe replacement market. Having completed previous Section 19 work on-site in association with the Holleran/Cafferkey partnership contractor, the works foreman was equipped with extensive knowledge of the pipe bursting technique.

The project required replacement of some 150m of existing 150mm diameter cast iron water pipe, which had recently experienced an increasing number of bursts. What made the replacement somewhat more complicated was that the pipe lay beneath 150mm thick asphalt road surface with a 200mm thick reinforced concrete basement, overlaying a soil/clay ground.

The water table level was also dependant on the tide, so the level varied in the ground. The road itself was heavily trafficked and was a bus route. The position of other utilities adjacent to the site also meant that careful consideration needed to be given in the choice of replacement method. Nearby plant included a 460mm diameter trunk water main, a 200mm diameter gas main, an high voltage electric cable and a 300mm diameter sewer.

Pipe bursting

Therefore, it was preferable to use the existing route of the water main to install the new pipeline. Pipe bursting was deemed to be the preferred option because it was a less intrusive technique, which could achieve the required pipe replacement over a shorter time period than traditional open cut options.

It was decided to use a hired pipe-bursting unit. The system chosen was a Hydroburst HB3038 Taper Thread Rod Burster, provided by trenchless equipment hire specialist U Mole. The bursting system was supported by a 180mm Coil Trailer.

As the workforce was not overly familiar with the technique or the system chosen, on site operator familiarisation, training and supervision was provided by U Mole¡¯s customer support, Matt Russum. Prior to starting the bursting works, trial holes were opened to check and verify the location and depth of the expected buried services along the route of the water main.

At the request of the highways authority, and due to other technical requirements including the maintenance of customer supplies during the work, the convenience of re-connecting the pipe work once installed and the location of two sets of traffic lights on the route, the project was split into two sections. The existing pipe was to be replaced with 180mm diameter, pre-chlorinated HPPE pipe over first a 100m length and secondly, a 50m length using coiled pipe provided by Polypipe. The pipe connections were ultimately achieved using electric fusion boxes from Fusion.

Set up for the project took four days including excavation of access holes on all the known services as well as other utility plant including gas, telecoms, electric cables, the sewer and the trunk main, together with launch and reception pits for the bursting equipment. Over-riders to back feed customers on a one-way feed that would otherwise be without supply during the work were also installed.

All customers that would be affected during the duration of the works were notified of the length of disruption they could expect. This included both the short interruption to cut and cap the main feed at either end of the replacement run and the longer ¡®all-day¡¯ disruption for customers on the length of main being renewed. All residents and businesses that may have been affected by the works were kept fully up-to-date on progress and had the facility to raise questions and concerns at any time regarding any issues they may have had.

For the bursting operation, initially the bursting rig was placed in the launch pit and the bursting rods were fed into the existing, isolated main. The new pipe was then attached to the pipe coil and pull back started with the existing pipe being burst as the rods were extracted.

Due to the adjacent plant, the access pits were used to ensure that the bursting head and new pipe did not interfere with the other existing services and where required the new pipe and bursting head were assisted around the adjacent plant. Once the pull through was completed, the bursting rig was removed and the main and services reconnected.

Customers on the long shutdown were issued with a ¡®boil water¡¯ notice as a precaution and later issued with ¡®safe to drink¡¯ cards on completion of satisfactory clear sample results. Side road connections were also left isolated until sample results passed the required tests.

The site was then reinstated to the required standards. This procedure was followed on both bursting operations.

The only significant problem encountered on the project was that, on excavation of the main for the first bursting run, it was found that the alignment of the main was altered by the inclusion of two 45¢ª bends installed back-to-back. This created a difference in alignment of some 600mm. It was decided to excavate some 2m either side of the bends and to cut out and remove them when the bursting rods were being installed. This allowed the rods to pull through the excavation without deflection during the bursting run.

Commenting on the Mill Road project, Paul Oxborough, site agent and foreman for the works for E&SW said: ¡°The location of the replacement works, the road layout, traffic flows and potential disruption to everyday life for those living and working along the route meant that we had to choose a technique that would minimise the impact on the local environment. Pipe bursting gave us that option.

¡°The support and back up provided by U Mole also enabled our crews, who were not overly familiar with the technology, to complete the bursting operations without any major problems. The insight this work gave us into the potential for the application of trenchless technology has been most valuable.¡±