Brixton to Honor Oak Tunnelling Project

Customer: Morgan Sindall

Site Owner: Thames Water

Value: £1.1m

FSD assisted Morgan Sindall in preparing the original tender for the Brixton to Honor Oak tunnelling project. One of the key deliverables of the project was a communications link between the two head houses. This link was to be effected by installing a dual redundant fibre optic cable, 5.2km long, within the tunnel.

The installation had to be able to withstand the flows and pressures of the water in this section of the London Water Ring Main, and was therefore required to run within ducts fixed to the wall of the tunnel. The distances involved were too long to allow blowing the fibres along the duct. The conventional method of installing the cable would be to run a polyethylene pipe/cable ducts in sections along the floor of the tunnel and then as a separate exercise pulling a fibre optic cable in stages flaking the cable in the tunnel after each section of duct and then welding the duct sections in situ. This was estimated at a cost of £500K and would have taken a significant time to install; there was also a risk that over time the duct could flood.

As part of the collaborative approach during a team meeting FSD challenged the requirement to install a duct as we believed there were products available that were used in other industry sectors that could be utilised.  We were tasked with providing an innovative alternative installation method of the fibre link.  An alternative of installing the duct in sections and blowing the fibre along each section and jointing the fibres was discounted as it was desirable to keep joints in the fibre to a minimum. The FSD tendering team reviewed the individual elements and identified that this one element was an area that potentially could be reduced and began investigation of alternative solutions. The result of the investigation was that we proposed a solution where a 25mm duct with a 36 fibre cable already installed in the duct was installed; this had not been used in this environment so we had to gain DWI approval. This proposed solution had an overall cost of circa £150K. Morgan Sindall secured the project and awarded the work to FSD.

In addition to sourcing the physical product we recognised that the installation method was critical thus our Operations Director sought the assistance of our supply chain partner F B Taylor to develop an alternative installation method.  The physical installation was undertaken by lowering two drums of duct down the shaft at Brixton and one at a time these were run through the tunnel network to Honor Oak. Following several meetings where various approaches were considered, the final installation proposal was that we would convert an electric luggage truck to hold the drum which would facilitate a significantly reduced installation period. 

We presented our proposal to the collective team and it was agreed that Morgan Sindall would include it in their final submission at a cost of £150K, a saving of £350K.

The installation of the two ducts in the 4.8K of tunnel was completed in two days, which was achieved by detailed planning and significant preparatory works which consisted of drilling the fixing holes in the tunnel liner; there were 3500 holes drilled and anchors installed at the 8 o’clock position in the concrete liner. FSD designed a bespoke stainless “butterfly” clip specifically for these tunnel projects.

After initial installation of the ducts they were pressure tested to 6 bar to ensure the integrity of the ducts. After testing, the ducts were clipped to the tunnel liner utilising the clips in a period of 5 days.

This installation also had the advantage that the fibre optic could be tested within the duct prior to installation, and that during installation the fibre cable was fully protected by the duct throughout the operation, thereby reducing the risk of damage and consequently keeping cost increase and programme disruption to an absolute minimum.

The installation incurred no variation costs on the fixed price. This part of the project was deemed so successful FSD were awarded the same scope of work for the Stoke Newington project.