The development of London Crossrail is widely recognised as one of Europe’s largest infrastructure projects. The modern rail link that will run for 21 kilometres (13 miles) at 40 metres (131 feet) below the city will dramatically change public transport for millions of commuters.
But Crossrail is not the only project tunnelling under London. Since 2016 construction has been underway for the London Super Sewer, a 25 kilometres (16 miles) long, 7.2 metres (24 feet) wide pipe, which will run through the city in a bid to clean up the River Thames as it battles to hold off increasing effluent generated by a growing population.
The project is the second time in 150 years that the London sewage network has undergone a major overhaul, and with a six-year timeline and £5 billion price tag, it has its detractors. But with over 39 million tonnes of sewage seeping into the Thames every year, this mammoth construction project, officially named the Thames Tideway Tunnel, was awarded the green light.
A Victorian Solution
In 1858, Sir Joseph Bazalgette was commissioned to tackle the problem of the poor sewage system for London. The River Thames essentially operated as an open sewer for its two million inhabitants, leading to the risk of serious disease and exuding a powerful stench along its banks. In the newly rebuilt Houses of Parliament sheets soaked with disinfectant were hung up in an attempt to disguise the smell. The Bill passed through Parliament with ease, and Bazalgette set about constructing the system that is still in operation today.
Built between 1859 and 1865, the visionary engineer constructed 1,800 kilometres (1,100 miles) of new underground tunnels and introduced a ”combined” system to capture both rainwater runoff and the waste produced by up to four million Londoners. To prevent sewage backing up and flooding properties, the system has the ability to overflow into the River Thames through 57 combined sewer overflows (CSO) along the banks of the river. In Bazalgette’s time, this happened once or twice a year, whereas nowadays it’s almost a weekly occurrence.
This innovative network of sewers now service the waste of nine million people and need constant maintenance to work at capacity. The system is under pressure from the development of high rise residential properties across London, and the demands of a growing population, which flushes up to 39 million tonnes of combined sewage into the River Thames each year.
The Thames Tideway Tunnel
Through a series of tunnels, shafts and pumps, the Thames Tideway Tunnel will run mostly under the tidal section of the River Thames through central London to facilitate the capture, storage and transporting of almost all the combined raw sewage and rainwater discharges that currently overflow into the river. The waste will be treated at a plant in the East of London after which the clean water can be released back into the river.
There is no doubt that the Tideway Tunnel project is a massive undertaking, incorporating 4,000 employees working over 24 construction sites across London. It has not been immune to delays, with teams working around the clock to stay on schedule where required.
While most of the work is happening deep under the city, the project’s impact has been felt above ground too. Residents living along the river, close to the access points, have been offered support such as triple glazing for windows and holidays during times of worst disruption to ease their frustrations.
One business victim of the development is the London Duck Tours, who had to give up its river access to one of the construction sites. The company was unable to secure an alternative launching point for the river section of its city sightseeing tour, and the iconic yellow amphibious vehicle anchored up in 2017.
Tunnelling Through History
The project has employed four bespoke Tunnel Boring Machines (TBM) which are cutting out the main tunnel at a depth of up to 70 metres (230 fee). At these depths, the machines are drilling below the Tube and Crossrail lines into unchartered territory. The teams have brought in scientists and geologists to help them navigate safely through rock seams which include fossils and fissures of water untouched for millions of years.
Working in a large, historic city such as London adds extra challenges which could severely impact the project. Before tunnelling could commence, the team had to secure an underwater scan of the riverbed to ensure no unexploded World War II bombs lay at risk of being disturbed. With the help of divers, they were given the all clear.
The project has also included the support of archaeologists to ensure that construction of the modern sewer is respectful of the way of life of past Londoners. The discovery of a Saxon fish trap at one site required a revision of the plans.
Working with the River
An estimated 1.5 million tonnes of earth will be displaced in the drilling of the main tunnel, which will be transported by boat to landfill 48 kilometres (30 miles) from the construction site. This approach removes lorries from the already congested road networks but is also giving employment to mariners in the London area. There’s also a nice symmetry that the project to repair the river is working alongside it to help deliver that objective.
Few people outside the construction industry understand the full expanse of what is needed to build and maintain our world’s growing cities. Working with the natural environment, communities, current infrastructure and more, builders have an increasingly vital role to play in addressing growth challenges across the globe. When the Super Sewer is completed in 2023, London will have a sewage system which supports the growing city and provides a better environment for all its inhabitants.