16km (10 mile) England High Speed 2 (HS2) Chiltern Hills Tunnel

North Portal: (Satellite, nothing shows on the map accessed in May 2024)

South Portal: (Satellite)

This is the longest tunnel on the HS2 route between London and Crewe. "The two TBMs that are being used to create the ‘twin bore’ Chiltern Tunnel were launched in the summer of 2021. TBM Florence completed her drive in February 2024 and TBM Cecilia completed her drive shortly after in March 2024." [hs2]

The tunnel boring began at the south portal, so that is where the TBM's were assembled, the tunnel lining segments were built, and the slurry was processed into chalk cakes. The chalk cakes will be used to create a new chalk grassland.

1:11 video @ 0:07 

Look at all of the rebar it broke through.

1:06 video @ 0:12

The TBM's bored 5.6m (18') diameter tunnels at an average pace of 16m (52') per day with a maximum depth of 80m (262'). The geology varies and includes chalk and flints. [BornToEngineer]

This source specifies a significantly larger diameter.

h2

Mammoet posted three photos with the comment:

🚄 Move3D software makes HS2 tunnel boring machine dismantling more efficient 🚄 

Digital twin proves that a lower capacity crane could do the job just as effectively, despite unknown center of gravity of the cutter head.

Read more: https://mmoet.me/44Ph41L

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Much of the chalk from the spoils is going to be used to transform the construction land scar into a chalk grassland.

Satellite

h2_green_corridor
"Chalk grassland – a type of calcareous grassland – is a habitat of international conservation importance mainly found on limestone and chalk valleys of south-east England and the Isle of Wight. As part of the ambitious scheme, 90 hectares of chalk grassland will be seeded into re-profiled soil layers using the nutrient poor subsoils on the site and mixing these soils with chalk from the tunnelling and recycled concrete and aggregates from construction works. This will sit alongside new areas of woodland, wood pasture and wetlands, including almost 65,000 trees and shrubs of 32 species and nearly 3.5km (nearly 2 miles) of new hedgerows on the western slopes of the valley of River Colne. Lime-rich, but low in nutrients, the thin soil holds little water and heats up quickly. These conditions encourage a huge variety of smaller herbs and wildflowers and over 40 species can be found in one square metre of grassland, including some of the UK’s rarest orchids and invertebrates. Only 700 hectares of chalk grassland exist across the whole of the Chilterns AONB."

A 4:27 video showing not only the inside of the TBM, but also the machine that lays the concrete at the bottom of the tunnel.