Tunnelling feats of engineering

tunnelling machineAs one marathon amount of tunnelling is just completing another is about to begin.

The 26 miles of crossrail tunnelling, linking rail services from Reading and Heathrow in the West to Shenfield and Abbey wood in the East finished in June after 3 years of constant tunnelling. 8 giant tunnelling machines were used constantly to make the network of new rail tunnels, and whilst there are still stations and platforms to construct it is hoped the civil engineering work will be complete in 2017 with the new rail services starting from 2018.

The new services will allow an extra 24 trains an hour to run during peak services and will increase rail capacity by 10% carrying 72,000 passengers per hour through the new tunnels. 1.5 million more people will be able travel to within 45 minutes of central London.

However, as one feat of tunnelling engineering ends another is about to begin. The Thames Tideway Project preliminary construction works begin in 2016, with the proposed 4 years of tunnelling beginning in 2017.

The project will involve 24 construction sites, 70 worksites, a host of project staff and contractors and will last up to six years in total.

The existing sewer system, built in the Victorian era can no longer cope. Drastic action has to be taken if we are to stop the Thames filling up with pollution. Currently, 2mm of rain can result in up to 57 combined sewer overflows discharging in to the river. At current rates this means that we discharge 39 millions tonnes of sewage into the river every year. Without the new sewer system this would rise to 70 million tons per year within 10 years. The year on year increase and the impact if nothing were done doesn’t bare thinking about.

Running 20 miles from east to west London, the Thames Tideway Tunnel or ‘Super Sewer’ will be up to 65 metres below ground and roughly follow the route of the River Thames, running through all sorts of soils and below all sorts of structures. It will connect 34 of the worst polluting sewer overflows as identified by the environment agency and capture the sewage before it spills into the river. From there it will be transferred to the Beckton sewage works to be treated.

This is another massive feat of engineering and is the biggest investment made in the sewer system since the 1850s. Innovative engineering design has already reduced the initial proposed length of the sewer and the number of constructions sites originally proposed.

The first year of construction will be taken up with the building of the main construction site and facilities and the sinking of the shaft from which the tunnelling will begin. As the tunnel extends concrete sections will be transported and put in place behind the tunnelling machine. At the same time, soil and slurry will be removed to the surface and disposed of.

And, as with Crossrail, once the tunnelling begins, it will continue 24 hours a day, below the streets of a busy London until it is complete.