Seven Sisters Phase 3: 200m of 900mm SDR 26 PE 100

It is always satisfying to see the pipe emerge at the winch!! Last week the final 200m of 900mm SDR 26 PE 100 Seven Sisters Phase 3 with MorrisonWS for Thames Water was successfully installed in a 36” cast iron under Myddleton Avenue.

This was a relatively short and straightforward pull for the Die Draw technique however this section presented some of the biggest Temporary Works challenges we have faced. We also had to accommodate a significant initial bend as the liner entered the host pipe from ground level. Although the setup was challenging, the actual liner pull was completely uneventful, with all loads matching our calculations.

In yet another industry first for Die Draw Ltd, we believe this could be the deepest deployment of the Die Draw process ever undertaken in a built up, congested metropolis.

Once again, our modelling of loads proved to be extremely accurate for the layout and ambient environmental conditions encountered, further demonstrating the reliability and robustness of our process.

So why were the Temporary Works so challenging?

Well, it’s the centre of London where nothing is straight forward. When constructing the reception shaft, historic brickwork was discovered that was initially thought to be the roof of a culvert. On investigation it was established that the brickwork was most likely to be the bed of an old water channel. The host pipe was very deep at the location of the launch shaft with a number of adjacent services in very close proximity.

Although trial holes had not found significant obstacles, the launch shaft was found to contain substantial brick structures thought to be associated with historic filter beds. The presence of electric, gas and water services close to buildings and street furniture presented additional challenges.

In order to lay the reinforced concrete base for the die restraint frame, excavation to ~6m depth was required. We believe this could be the deepest pipeline ever where this technology has been successfully deployed.

As always, it is a team effort that make these large projects such a success. A special mention should go to Morrison Water Services for the really high standard of the butt fusion welding critical to this process, where tie-in welds are required while the installation is paused, due to space restraints.

Congratulations to Thames Water on yet another successful Die Draw liner installation. We’re excited about our next project.