Severfield is assisting with the construction of a new tunnel under the Thames, linking Silvertown to Greenwich. This new 1.4-kilometre twin-bore road tunnel will be the first of its kind for over 30 years and will be excavated by the largest tunnel boring machine (‘TBM’) ever used in the UK – its cutter face has an impressive 12-metre diameter.

Severfield is providing the supply, design, fabrication, connection and delivery of up to 42-metre-long props at both sides of the tunnel. All excavation that is not being undertaken by the TBM will be supported by these props. In addition, we are supplying over 600 tonnes of waler beams, which are horizontal beams used to support the retaining sheet pile walls.

The standard method for installing props is to use grout-filled flat jacks (hydraulic pumps). Once the prestressed force is transferred into the prop, the grout cures, thereby locking it in position. However, due to certain technical aspects specific to this project, grout-filled flat jacks could not be used. Therefore, Severfield designed a bespoke hydraulic jacking system to prestress the required props with up to 50 tonnes of force.

Cognisant of the size of the props, Severfield designed transport frames that allowed for up to three prop sections to be transported to site in a single load. This reduced the number of lorryloads required, therefore reducing our carbons emissions and the risk of disruption to local transport. In addition, the project enabled us to make use of reusable props, which will be removed towards the end of the project and reused on future projects, reducing the overall impact on the environment and further reducing our carbon footprint.

A complex project such as this illustrates Severfield’s ability to think creatively and implement non-conventional solutions.