Thames Tunnel

Project Overview

The world-famous Thames (Brunel) Tunnel is built beneath the River Thames, connecting Rotherhithe and Wapping. The tunnel was originally designed for horse-drawn carriages but was mainly used by pedestrians and became a tourist attraction. In 1869 it was converted into a railway tunnel that is part of the now East London Line on the London Overground railway network with Up and Down lines.


Each track is on a concrete slab and the baseplates are ‘direct fix’ to the slab. There is a stray current issue due to the proximity of the Network Rail four rail system to the London Overground three rail system that causes rail foot corrosion at the low point of the tunnel where there is saltwater ingress from the Thames. The corrosion was at or beyond the maximum allowed and both tracks required rerailing to prevent potential rail breaks.


To address the rail condition, the two-stage solution was Stage 1 to remove existing deteriorated rail and to install Zinoco coated corrosion protected rail and in Stage 2 to change the non-insulated baseplates for new insulated baseplates. The rail has been changed and a bespoke baseplate design and procurement process is currently ongoing.

Scope of Works

  • Conduct planned intrusive investigations of the existing baseplates, anchors and pull-out tests.

  • Undertake Engineering reviews and surveys to investigate stray current, water ingress impacts and assess general constructability considerations in the constrained environment.

  • Complete remaining survey works of the Thames Tunnel

  • Early engagement of our supplier British Steel to obtain the best track replacement solution.

  • Ferroscan surveys of the tunnel to determine existing reinforcement.

  • Re-Rail both lines (over 800m) on Thames Tunnel to ensure continuing immediate operational safety of the line whilst baseplate design and procurement process occurred.


The client, London Overground (LO) required the Re-Railing of Thames Tunnel to be completed within a quick timeframe, as the existing Rails exhibit signs of heavy corrosion and contamination. LO looked to Cleshar to provide innovative measures to reach the project goal. The following innovations were implemented to achieve this:

  • Specially designed to perform in corrosive environments, Zinoco coated corrosion protected rail was installed on baseplates and this project is one of the biggest installations to date for this system/product. Supplier British steel stated on their website “We coated the rails on our new state-of-the-art coating line. Zinoco is a barrier coating with sacrificial protection so is the perfect solution for extending rail life in harsh environments, such as wet tunnels. Our team of commercial, technical and production experts worked diligently with Cleshar throughout this project, making sure they had exactly the right product at the right time for successful completion.” British Steel performed under severe business pressures of financial uncertainty to produce the rail to tight deadlines.

  • Cleshar and TFL Track and Civil engineering experts from an early stage identified risks and workable solutions to unique complex challenges such as product selection analysis, track gradient complexities, drainage issues and stray current impact assessments.  

  • Cleshar inhouse track and welding teams ensured the project was delivered on time utilising available possession and midweek night shifts in a heavily constrained environment. The corrosion was so severe in places that grinding and deep clean of the baseplates was required to enable the new rail to fit and be fastened down.

Benefits / Project Outcome

  • Successful delivery of a challenging unique physical and engineering project with no impact to the operational railway infrastructure.

  • This successful delivery allows the safety of the operational line to continue whilst enabling Cleshar and TfL engineering teams time to design a bespoke solution to the baseplate replacements in the next phase.




London Overground East London Line


Wapping St. to Rotherhithe St.

Programme Dates

Dec 19 – Oct 20