Breakthrough for London’s newest underground tunnel

Construction is currently ongoing in London, UK on the Silvertown Tunnel to address congestion in the Blackwall Tunnel.

This will be the first newly built underground road link between the two banks of the Thames in over 30 years.

The tunnel spans 1.4 kilometres and has two lanes on each side. It was excavated using a Herrenknecht TBM with a shield diameter of almost 12 meters, the largest ever used in the country.

The machine weighs 1,800 tonnes and is 82 metres in length. As of July 23, 2023, “Jill” had inserted 1,120 segmental rings, weighing approximately 70 tonnes each, to reinforce the tunnel.

The Riverlinx CJV joint venture completed the southbound tunnel breakthrough in mid-February 2023. Typically, Herrenknecht says, twin-tube tunnels are built using either two TBMs or a single TBM that is dismantled and returned to the original launch site for the second drive.

However, the Silvertown Tunnel project managers opted for a different, innovative approach. After completion of the first tunnel, the entire machine was rotated by 180 degrees to bore the northbound tunnel. This required the excavation of an 18-metre-deep and 40-metre-long open-top shaft.

Herrenknecht developed a special procedure to turn the 1,450-tonne shield machine for the project. The shield machine and cutting wheel were placed on a sled, which slid on cushions filled with compressed nitrogen.

Using pneumatic chain hoists, the machine was turned precisely and brought into the new position. This method had already been used successfully in Paris and on the new Stuttgart-Ulm railway line. The Herrenknecht specialists accomplished the 180-degree turn of the shield machine in London in a single day.