The engineering


At 25 kilometres long, up to 66 metres deep and more than seven metres wide, the Thames Tideway Tunnel is the biggest infrastructure project ever undertaken by the UK water industry.

It generally follows the route of the River Thames, enabling it to connect to the ‘combined sewer overflows’ (CSOs) dotted along the riverbanks, passing beneath all other infrastructure in London and through a variety of different ground conditions.

How do you build a tunnel under the River Thames?

World-class contractors are building the Thames Tideway Tunnel, offering sustainable, innovative and cost-effective methods of construction.

The project is split into three distinct sections, with three main ‘drive sites’ – sites from which we launch four tunnel boring machines (TBMs) to construct the main tunnel.

These giant, state-of-the-art machines, each custom designed to be as safe as possible, will burrow beneath the breadth of London – covering a distance wider than the EastEnders title card.

We’re also using two smaller TBMs to create two smaller connection tunnels.

What is a tunnel boring machine?

A TBM tunnels through the ground using its rotating cutterhead, simultaneously creating the tunnel walls with prefabricated segments of concrete. Spoil from the digging must be removed by conveyor (or by pipe, if the spoil is in a slurry form), while segments of concrete must be continuously delivered to front of the machine. The pressure from the surrounding earth must be counteracted and the machine must be fully ventilated.

These are just a handful of the challenges faced by a TBM at work. Our machines will be more than eight metres in diameter, longer than a football pitch, built to work around-the-clock and will excavate up to eight metres per day.

What is a tunnel boring machine?