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Flowtek HDD UK Limited was recently employed as Principal Contractor by Scottish and Southern Energy PLC along with project consulting engineer Veda Associates Limited to install a cable duct to carry a 33 kV mains supply beneath the Arborfield Bridge at Church Lane, Shinfield, Berkshire, UK. Located just south of the M4 motorway near the town of Reading, the installation was required to connect a new, large housing development in the area to the main power grid. 

PLANNING

As part of the planning operation, bore holes were dropped along the route where possible to determine ground conditions. A radar scan was also completed to locate any utilities and trial holes were used to prove these targets to provide a safe working route. Flowtek undertook the full design on this project.

These ground investigations showed that the conditions in the area comprised largely Gravel near surface with London clay laying below this. At the bridge site not only did the installation have to cross beneath one of the bridge foundations but also two water courses. This made any option other than a trenchless solution impossible. It was decided to utilise Horizontal Directional Drilling (HDD) to complete the works. Planning of the crossing showed that the drilled bore would need to pass some 24 m below the bridge foundation, so it was decided to install the cable duct with a 300 mm diameter bore. 

Special permission had to be granted by Reading University for the operation to be allowed access to the worksite selected for the drill set-up.

INSTALLATION

Using it's broad base of experience in the HDD field, Flowtek chose to utilise its Ditch Witch JT8020 drilling rig along with a 1,000 gal (4,500 l) mixing unity with a hopper and a twin 1,000 gal (4,500 l) mixing unit with a Gyro guidance system for the bore. 

The pilot bore was achieved with a Gyro based drill head of 8 in (200 mm) diameter. The pilot was reamed to size using Ditch Witch Kodiak Reamers of 12 in (300 mm), 16 in (400 mm) and 20 in (500 mm) diameter.

Once the main bore and reaming operations were completed, the team pulled in a bundle of two ducts using a barrel reamer lead. The two ducts comprised both 200 mm and 110 mm SDR11 Black Electric Ducts. The 200 mm diameter duct was installed to carry the main electirc cables with the 110 mm diameter duct being used as the comms duct. All pipes butt-welded to current water standards and internal/external de-beaded. A butt-fusion machine was utilised to create the pipe strings required each to a length of 324 m. A CCTV survey of the completed pipework was undertaken prior to installation to prove all internal beads had been removed. 

The programme of work commenced on 28 August 2021 with the trial holes. Traffic Management was set up to enable the trial holes to be carried out. Two trial holes were placed in theroadside verge to determine which utilities existed and at what depths. An electromagnet utility survey was also carried out. 

The drilling rig and support equipment was mobilised to site on 4 October 2021 with the work site and traffic management around the site being in place by 5 October. A check utility scan was then completed and the necessary access pits excavated. The drill rig and guidance system was set-up on 6 October and drilling commenced on 7 October 2021. 

On completion of the pilot bore and reaming stages and preparation of the pipelines and internal confirmed, the pipe installation took placeon 18 october 2021. The site was cleared completely by 20 October with traffic management and complete demobilising happening on 22 October.

During the course of the installation works, the only problem encountered was flooding in the access field due to heavy rainfall at the end of the completed HDD work. Flowtek had constructed its own site compound and welfare facilities. With this being full design and delivery project, Flowtek had allowed for this area to be matted out so that it did not destroy the field due to construction traffic. This meant that the crew simply had to wait for the water table to go down before removal of all matting and no damage was done to the field. Flowtek also cleared a running ditch that was over grown for the water to flow as it should. 

Commenting on the project for Flowtek Chris Preston, Managing Director said: 

"This was a very challenging project with drilling down to a depth of 24m. However with the expert guidance of the Gyro Equipment giving pin point accuracy throughout the bore and with a dedicated and experienced drilling team, the project was completed to a very high standard and within the predicted time frame. The Ditch Witch JT8020 delivered with excellent results along with support from Ditch Witch UK. A big well done to all the teams and suppliers involved for a successful installation."