Sewer Surveys UK Ltd and Bridgeway Consulting worked in partnership to carry out a CCTV inspection survey of a siphon culvert that runs directly under the Great Western Main Line railway between London and Bristol.

Due to the location of the culvert being next to a railway and the Inlet and Outlet both being on the public highway, our first mission was to gain safe access to the culvert, we achieved this by using our PTS trained staff and removing some of the fencing between the railway and the public highway. The siphon was a 300mm diameter concrete pipe which was approx 40m in length but from the Inlet there was a drop of approx. 10m under the railway before it climbed back up to the Outlet, this resulted in a large volume of water standing within the siphon. This culvert had not been surveyed for many years so experience told us that the siphon would probably contain debris and silt at the bottom.

Firstly, we had to isolate the watercourse of any incoming flows and pump out the water within the siphon using a large volume tanker. Once the siphon was empty of water we carried out a CCTV survey to the bottom, only at this point did we visually identify approx 30% of silt and debris. Secondly, following on from our CCTV Survey we had to clean out the bottom of the siphon, to do this we used high pressure water jetting with the jetting unit and suction facility. Once the cleaning was completed, we carried out a further CCTV survey and achieved a full survey of the siphon.

The survey, isolation of the watercourse, tankering and jet cleaning was all safely completed within 2 days with no disruption to the railway and no flooding or pollution incidents.