Forming a core component of the most ambitious UK roads project for a generation, the tunnels and approaches contract includes the design and construction of twin tubes under the River Thames located up to 53m below ground.

With an excavated diameter of around 16m, the two 4.2km (2.6 mile) tunnels will be designed as free-flowing components with three lanes of unidirectional traffic travelling at 70mph in each tube. The scope also includes short sections of cut and cover, the portal buildings, 1km of approach roads and the tunnel systems’ engineering.

Both TBMs will be launched from the north portal. Tunnelling will mostly be in the chalk (white limestone) although Highways England envisages complex mixed-face conditions which could require significant ground treatment. Pressures of around 5.5bar are anticipated below the river.

A total of 27 cross passages between the two tubes will be spaced 150m apart but will be free of any equipment and services as the huge diameters involved allow abundant space in the invert below the road to house equipment, cable runs and other services; this will include a 5m-wide access route.

With 23km (14.3mi) of new road, the Lower Thames Crossing (LTC) aims to almost double road capacity across the Thames east of London. Works on the mega project could start in around 18 months, and would provide a huge jobs boost for UK infrastructure. Initial technical consultations for the scheme were provided by a Jacobs Arcadis Cowi joint venture.

Keith Bowers, Lower Thames Crossing’s Tunnels and Systems Director, said: “This contract is unparalleled in its ambition, and we need the right partner to match that ambition. From our bidders we’re looking for outstanding construction, health, safety and wellbeing performance.

“We are setting priorities in our contracts that will reward excellence during delivery by offering an enhanced share of cost savings for high performance in areas including health and safety, customer focus, delivery, environment, people and communities, and economics.”

A bespoke design and build form of the NEC4 Engineering and Construction Contract (ECC) will be used for the Tunnels and Approaches package. It is the first of the three main works contacts to be procured for the scheme, with the Roads North and the A2-M2 contracts expected to be announced early in 2021.

A planning application for the scheme was submitted in late October. A decision is expected from the Secretary of State for Transport in 2022, with construction expected to start later that year.

The contract notice will be published in November in the OJEU. Before the end of 2020, bidders will be asked to return a selection questionnaire. Highways England says it expects three applicants to be shortlisted to move forward into the competitive dialogue stage, with the contract award anticipated in 2022. The tender process will be undertaken via the Bravo eSourcing platform. Interested parties can register via https://highways.bravosolution.co.uk