The 15.5-mile (25-kilometres(km)) Thames Tideway Tunnel will modernise London’s Victorian wastewater infrastructure, dramatically improving the water quality of the River Thames and ensuring London has a wastewater system equipped to meet its needs for the next century.

As recognised by the Environment Agency, the development, combined with the completed Lee Tunnel and improvements to five sewage treatment works, is essential to ensure compliance with the EU’s Urban Waste Water Treatment Directive.

AECOM is delivering design services for the tunnel’s 7.5-mile (12-km) central, and largest section, and to support the consenting process. The entire 15.5-mile (25-km) tunnel generally follows the route of the River Thames, connecting to overflows along the riverbanks.

The complex central section of the tunnel will pass through a variety of different ground conditions, including London Clay, Lambeth Group, Thanet Sands and Chalk.Summary of engineering problems encountered with the Lambeth Group There are a total of 26 shafts, drop, vortex and connection shafts plus tunnel boring machine launch shafts, with shaft depths varying between 10 and 70 metres. It will be built under London’s existing underground infrastructure, in close proximity to tube lines and utilities.

The designs will also need to minimise disruption to the busy, compact London streets above, and will involve a complex programme of geotechnical instrumentation monitoring.