Kick-off at HS2 with groundbreaking forepoling technology

The Chilterns Tunnels and Colne Valley Viaduct main works civils contract is a key section during phase one of the High Speed 2 (HS2) project, connecting London and Birmingham. Lot C1 was awarded to ALIGN JV and consists of a 21,6 [km] long high-speed railway line between the Colne Valley and the Chilterns, including the 15,8 [km] long Chiltern twin tunnels as well as the 3,5 [km] long Colne Valley Viaduct.

A major portion of the Chiltern twin tunnels will be excavated with two TBMs, with a final inner diameter of 9,1 [m]. Two running tunnels are connected to each other with 38 conventionally excavated cross passages, located every 500 [m]. The ground mainly consists of fractured chalk with different degrees of weathering.

Prior to TBM installation, the two Southern tunnel portals have been stabilized by a dense soil nail pattern. To secure a safe launch chamber for the TBMs, installation of a double pipe umbrella was chosen as suitable measure by the civil works contractor and design team. Fully mechanized installation of the pipe umbrella was a mandatory requirement, use of the AT – Automation unit developed by DSI Underground did fully comply with this requirement.

The AT – Pipe Umbrella System from DSI Underground is a pre-support measure used to increase the stability of excavations in weak ground. DSI Underground’s proprietary squeezed connection for pipe umbrella pipes with improved load-bearing capacity has been chosen as a replacement for the tendered conventional threaded connection. The proprietary squeezed connection technology features enhanced working safety and proven cycle time savings.

Construction of the tunnel portals has been successfully completed in 2020, featuring the kick-off of this time critical and public sensitive project. Safety, service, and support provided by DSI Underground was appreciated by the civil works contractor.