10-mile Chiltern tunnel drive nears completion

AFTER a two-and-a-half year drive under the Chiltern hills, tunnelling machines Florence and Cecilia had reached the Chesham Road intervention shaft by mid-December.

Heading north from London (the direction from which the twin bores are being excavated), it is the fifth and final shaft along the 10-mile route of the tunnel. In reaching this point, the two machines have completed 90% of their work, already excavating around 2.8 million cubic metres of chalk and flint.

Hidden behind trees, the top of the 42 metre (138 feet) deep shaft near Great Missenden, for emergency access, will have a ‘headhouse’ above it, designed to resemble local farm buildings.

Excavation of the four other shafts for ventilation and emergency use (near Chalfont St Peter, Chalfont St Giles, Amersham and

Little Missenden) has been completed, with attention turning to building their internal structures and ‘headhouses’.

Ninety engineers were involved in the operation to assemble the 1,600 tonne boring machine which will complete the second bore of the 3.5 mile-long Bromford tunnel, between Water

Orton in North Warwickshire and Washwood Heath in Birmingham.

Most of it previously formed part of Dorothy, the TBM used in the excavation of Long Itchington Wood tunnel. It is due to launch in spring from

Water Orton, where sister TBM Mary Ann began its work on the first bore last August. Mary Ann is set to break through at

Washwood Heath at the end of this year, with the as-yetunnamed second TBM due to complete its bore in mid-2025.

The work site at the 42 metre (138 feet) deep shaft at Chesham Road near Great Missenden, one of five which will provide emergency access to the Chiltern tunnel. The tunnel boring operation below had reached this point by mid-December. HS2