HS2's tunnel boring machines (TBMs) named "Florence" and "Cecilia" have reached the Chesham Road intervention shaft. 

The two mammoth machines, each weighing 2,000 tonnes, are on course to complete their challenging 10-mile journey under the Chilterns next year.

HS2 states the machines have completed approximately 90 per cent of their two-and-a-half year drive from the M25 to South Heath in Buckinghamshire, tasked with creating the twin-bore tunnel.

The grand scheme of HS2 requires 64 miles of tunnelling.

As such, five TBMs are currently operational, three more are prepared to commence, and another two are expected to arrive next year.

Upon completion, HS2 is projected to enhance connections between London, Birmingham and the North, as well as provide relief from congestion on the busiest section of the existing West Coast Main Line.

Mark Clapp, HS2 Head of Delivery, said: "Once complete, HS2 will transform journeys between London and the West Midlands and free up space on the busiest part of the West Coast Main Line.

"We're making great progress in the Chilterns, with 90% of the tunnel excavation now complete.

"That's an incredible engineering achievement and I look forward to the breakthrough, next year."

Each Chiltern TBM, a 170m long self-contained underground factory, lines the tunnel with 56,000 concrete segments which are then grouted into place as it moves forward.

The TBMs, launched during the summer of 2021, are custom-built for the geology of the Chilterns, and have succeeded in excavating nearly 2.8 million cubic metres of chalk and flint to date.

In addition to boring the tunnels, engineers have completed the excavation of four other shafts slated for ventilation and emergency access near Chalfont St Peter, Chalfont St Giles, Amersham and Little Missenden.

The ongoing efforts now aim to erect internal structures and surface headhouses.

Didier Jacques, Underground Construction Director at Align, a joint venture comprising Bouygues Travaux Publics, Sir Robert McAlpine, and Volker Fitzpatrick that operates the TBMs, said: "With our first TBM Florence having reached our fifth shaft at Chesham Road and our second TBM Cecilia due to reach the shaft shortly, this a great achievement for not only the tunnelling team, but also the supporting teams on the surface at the South Portal, manufacturing the concrete segments required to line the tunnels and processing the spoil from the tunnels.

"We are looking forward to continuing the good progress with the TBMs, which are due to complete their drives early next year."

Around 3 million cubic metres of material, largely chalk and flint, is expected to be excavated during the construction of the tunnels to be utilised for landscaping.

Following completion, the temporary structures at the south portal will be removed and the site re-landscaped with approximately 90 hectares of chalk grassland habitats - a nod towards environmental conservation.