Lower Thames Crossing ground preparation: geotechnical lessons for TBM design
Reviewed by Joe Ashwell
First reported on New Civil Engineer
30 Second Briefing
Ground preparation is under way to tackle sub‑optimal geology ahead of Lower Thames Crossing tunnelling, with drives under the river not due to start until late 2028. Tunnels director Alastair Lewis is sequencing works to deal with weak alluvium and variable chalk, aiming to stabilise the alignment before launching large‑diameter TBMs for the twin road tunnels. Early treatment of poor ground conditions is intended to reduce settlement risk for the approaches and portals and to de‑risk TBM performance beneath the Thames.
Technical Brief
- Sequencing of enabling works is being used as a safety control to avoid concurrent high‑risk activities.
- Early ground treatment is explicitly framed as a means to reduce intervention needs during TBM drives.
- Safety risk assessments are being updated iteratively as new geotechnical data from the corridor becomes available.
- Lessons on pre‑conditioning weak river‑crossing ground are expected to inform future major tunnel schemes.
Our Take
With tunnelling on the Lower Thames Crossing not due to start until late 2028, UK contractors have an unusually long lead-in to refine ground treatment and monitoring strategies, which in our database is less common on major geotechnical projects where enabling works and drive start dates are typically much closer together.
Among recent UK geotechnical ‘Projects’ and ‘Safety’ pieces in our coverage, several involve legacy ground risks around existing transport corridors, so the extended programme on the Lower Thames Crossing is likely to be used to de-risk interfaces with current Thames crossings and dense utility corridors before TBM launch.
The long horizon to 2028 also suggests that procurement for specialist ground improvement, instrumentation and emergency intervention systems will be staged, which can spread contractor and supplier demand across multiple UK megaprojects rather than peaking simultaneously, a recurring resourcing issue in other large infrastructure items in our database.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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