Geo-data driving the Lower Thames Crossing

Mapping the route with a bespoke campaign

The investigation formed part of the Phase 2 ground investigation works for the Lower Thames Crossing (LTC) project, a nationally significant infrastructure scheme led by National Highways.

This overwater investigation focused on the river section between Gravesend and Tilbury, where we completed 25 boreholes using jack-up barges. The scope included cable percussive and rotary drilling to depths of up to 86 metres below the riverbed, in situ testing such as pressuremeter and permeability tests, downhole geophysics, and extensive laboratory analysis of soil and water samples.

To ensure stable and safe drilling platforms in the river environment, we utilised jack-up barges. Each barge was equipped with specialist tools and testing equipment tailored to the specific requirements of the boreholes; the Aran 120 focused on geophysical testing, while the Skate 3E was configured for high-pressure dilatometer testing.

To assess groundwater flow characteristics, which show how easily water can pass through the soil and chalk at different depths and rates of pressure, using advanced logging tools, we carried out permeability testing using single and double packer methods. Soil and water samples were collected for both geotechnical and geo-environmental laboratory testing, giving us the full picture of the subsurface. A comprehensive wireline geophysical logging suite was also deployed, including acoustic and optical televiewers, resistivity, conductivity, flow, spectral gamma, calliper, gamma-gamma density, p- and s-wave, and downhole magnetic resonance methods to characterise the chalk.

Meticulous planning for the Thames

The River Thames is a heavily trafficked waterway, so conducting intrusive investigations in this environment required careful planning and coordination. We needed to consider the tidal conditions which significantly influenced our access to planned borehole locations, particularly in intertidal zones where low water levels restricted barge movement. Crew changes and equipment transfers also had to be scheduled around tidal windows and weather conditions. 

Several boreholes were located within or adjacent to the river’s main navigation channel, so we worked closely with the Port of London Authority and the Harbour Master to develop a plan of action. In order to ensure safe movement of marine traffic we established exclusion zones around the jack-up barges, and a one-way navigation system was implemented during operations in the channel. Additional constraints included the potential presence of unexploded ordnance, restricted visibility due to fog or low light, and environmental sensitivities along the planned route. The site was classified as a “yellow” zone which has additional environmental protections, so we used drilling fluid recirculation systems to manage waste and protect aquifers.

Joint effort for top safety and quality standards

The investigation was a collaborative effort between us, AECOM on behalf of PerfectCircle JV, and other subcontractors under the early contractor involvement framework. This approach enabled early engagement between the end client National Highways, designers, and contractors, fostering a shared understanding of project objectives, constraints, and safety expectations.

To maintain high standards of performance and compliance, daily briefings, risk assessments, and safety audits were conducted. Health, safety, and environmental management were central to the project’s planning and success. All personnel underwent site-specific inductions and employer project induction centre training.

Outcomes and impact

The data we collected was instrumental in the successful Development Consent Order application that National Highways needed to progress the LTC project.

Our critical Geo-data on the geological and hydrogeological conditions beneath the River Thames was essential in assessing geohazards and associated construction risks, and informing the development of mitigation strategies for potential environmental impacts.

The successful delivery of the overwater ground investigation marked a key milestone in the progression of LTC and demonstrated the value of integrated planning, technical expertise, and collaborative delivery in complex infrastructure schemes.