National Highways' Lower Thames Crossing project is the most ambitious road scheme in a generation. When built it will ease congestion on the Dartford Crossing by almost doubling road capacity across the Thames by connecting to the existing road network from the A2/M2 with two tunnels (one southbound and one northbound) beneath the river east of Gravesend and Tilbury.
As the tunnels will be bored by a large diameter Tunnel Boring Machine, Ground Investigation (GI) works were undertaken to provide information for design of the infrastructure including the tunnel.
For the tunnel, the GI comprised overwater boreholes from two jack-up barges at around 25 locations across the river, within the authorised navigation channel and close to the operational Port of Tilbury. The works required a Temporary River Works Licence (TRWL) from the Port of London Authority as the Statutory Harbour Authority.
What we did
To support successfully gaining the TRWL, NASH Maritime undertook a navigation risk assessment, working with AECOM on behalf of National Highways, to understand how the works could be undertaken safely whilst minimising impact to the range of navigation users including the adjacent Port of Tilbury.
Our assessment was undertaken drawing upon our extensive experience across the Thames and in accordance with the PLA authorised navigation risk assessment methodology.
We began by developing a baseline understanding of vessel traffic and navigation in the area by analysing AIS data, supplementing this understanding through engagement with statutory consultees and local stakeholders, and historic incident records.
Working closely with the PLA and their pilots, we also undertook full bridge navigation simulation trials to provide additional quantitative input into the risk assessment by validating potential hazards and developing risk control mitigations including amended operational river practices to enable the continued safe navigation whilst the jack-up barges were in the river.
From this baseline understanding we assessed impact to navigation safety risk and identified which additional risk control measures could be used to mitigate the increase in navigation risk during operations.
The GI across the river was successfully completed in 2019.
National Highways manages and improves England’s motorways and major A roads, to help customers have safer, smoother and more reliable journeys - learn more about them and the Lower Thames Crossing here.
