The second 10.25m diameter Herrenknecht TBM building HS2 under the Chiltern Hills has broken through at the tunnel’s northern portal, completing a journey that began in June 2021.
Named Cecilia, the TBM has driven for 16km underground to join twin sister machine – Florence who arrived at the site near the Buckinghamshire town of Wendover on 27thFebruary, after completing her adjacent tunnel drive.
Between them, the two 2,000 tonne machines have built the twin bore tunnel at depths of up to 80m and excavated three million cubic metres of chalk. Each machine has lined them with 56,000 pre-cast concrete segments, grouting them into place whilst boring at an average speed of 16m per day.
Both machines launched from the tunnel’s south portal, near the M25 motorway, were operated by HS2’s main works contractor, Align – a joint venture formed of three international infrastructure companies: Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick. The machines are made in Germany by TBM specialists Herrenknecht.
Align’s Underground Construction Director, Didier Jacques said: “Ten miles is a long drive for a TBM, with a typical average being around three miles. The complexity and technically challenges of completing such a long drive for both our TBMs has been significant, however I am delighted that as a team, we have risen to the challenge.
“Both TBMs were designed in partnership with Herrenknecht and incorporate innovations and technologies that have been introduced on TBMs in the UK for the first time, to enhance performance and safety. This includes ‘semi-continuous boring’, allowing our TBMs to build the rings that line the tunnels without pausing.”
In total over 450 people have worked on the tunnels over the last three years, including a dedicated production team who made 112,000 precision-engineered, fibre-reinforced concrete tunnel wall segments on site at a purpose build temporary factory – and a team processing the spoil from the tunnels.
Completion of tunnelling under the Chilterns follows recent publication of HS2 Ltd research showing how high-speed line’s arrival in the West Midlands will give a £10bn economic boost over the next decade, with new development around its stations at Birmingham’s Curzon Street and near the city’s airport and the NEC.
Herrenknecht
Pioneering Underground Technologies - Herrenknecht AG is the technology and market leader in mechanized tunnelling. As the only company worldwide, Herrenknecht delivers cutting-edge tunnel boring machines for all ground conditions and in all diameters - ranging from 0.10 to 19 meters.
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