Chesham Road intervention shaft

There are four ventilation shafts and one intervention shaft in the tunnel across the Chilterns. These will also be used for emergency access during operation. The intervention shaft is alongside the B485 Chesham Road in South Heath and just 1km from the north tunnel portal.

The shaft does not have ventilation fans nor a headhouse basement. It was built using the caisson construction method. The site also houses an auto-transformer station. The shaft depth is 43.5 metres and the tunnels are 33 metres below ground. The tunnel boring machines reached here in December 2023. The shaft is due to be completed by March 2025.

The approved access route is via the B485, A413, A355 to Beaconsfield then the A40 and the M40. Public Right of Way (PRoW) GMI 33/4 will be temporarily diverted before being reinstated along its original alignment.

The route north passes under Chesham Road and King’s Lane and then close to Sibley’s Coppice before passing under Frith Hill as it approaches the north tunnel portal.

*Two sinkholes appeared in a field to the south of Frith Hill as the TBMs approached the north tunnel portal in February 2024. A combination of disturbance from tunnelling, and potentially recent rainfall, weakened pre-existing weak spots which then collapsed to form the sinkholes.
The holes were remediated by compaction of topsoil. The area was then monitored to ensure the ground remained stable.

Chesham Road intervention shaft looking north – May 2016 (07_69)
Chesham Road intervention shaft looking south – Mar. 2019 (07_68)
Intervention shaft headhouse from Chesham Road – Feb. 2024 (07_100)
Frith Hill looking east across the tunnel crossing – Feb. 2024 (07_99)
Looking south from Frith Hill towards Sibley’s Coppice – Feb. 2024 (07_98)
Looking south from Frith Hill towards Sibley’s Coppice – Feb. 2024 (07_97)
Sink hole looking south towards Chesham Road – Feb. 2024 (07_96) Mike Johnstone
Chesham Road intervention shaft looking south – Jan. 2024 (07_95)
Chesham Road intervention shaft headhouse construction- Jan. 2024 (07_94)
Chesham Road intervention shaft headhouse construction- Jan. 2024 (07_93)
Shuttering for construction of the headhouse walls – Jan. 2024 (07_92)
The top of the intervention shaft – Jan. 2024 (07_91)
Chesham Road intervention shaft looking over the auto transformer station base – Jan. 2024 (07_90)
Chesham Road intervention shaft and the north tunnel portal – Jun. 2023 (07_89)
Chesham Road intervention shaft looking north east – Jun. 2023 (07_88)
Chesham Road intervention shaft looking south – Oct. 2022 (07_87)
Chesham Road intervention shaft looking north – Oct. 2022 (07_86)
Chesham Road looking east towards the intervention shaft – Sep. 2022 (07_85)
Construction of the final section of the caisson – Sep. 2022 (07_84)
Final caisson section awaiting concrete pour – Sep. 2022 (07_83)
Looking north from the final caisson section – Sep. 2022 (07_82)
Concrete pouring to the final caisson section – Sep. 22 (07_81)
Chesham Road intervention shaft looking south – Jun. 2022 (07_80)
Looking north to the shaft construction – May 2022 (07_79)
Looking north to the shaft construction – May 2022 (07_78)
Steel reinforcement for caisson section – May 2022 (07_77)
Looking down the shaft from the construction platform – May 2022 (07_76)
Caisson excavation – May. 2022 (07_75)
Chesham Road vent shaft looking east from PRoW 33/4 – May 2022 (07_73)
Chesham Road vent shaft looking east – May 2022 (07_72)
Looking north from the Chesham Road intervention shaft towards the north tunnel portal – Apr. 2022 (07_71)
Chesham Road intervention shaft looking north – Apr. 2022 (07_70)
Chesham Road intervention shaft looking north – Nov. 2021 (07_67)
Chesham Road intervention shaft looking south – Nov. 2021 (07_66)
Chesham Road looking west – Jul. 2021 (07_60)
Chesham Road looking south – Jul. 2021 (07_59)
Chesham Road looking south – May 2021 (07_55)
PRoW GMI 33/4 diversion looking south – May 2021 (07_54)
PRoW GMI 33/4 diversion looking south – May 2021 (07_53)
PRoW diversion – May 2021 (07_49)
Chesham Road intervention shaft looking north – Apr. 2021 (07_44)
Chesham Road intervention shaft looking south – Apr. 2021 (07_43)
Chesham Road looking west – Apr. 2021 (07_39)
Chesham Road looking south – Apr. 2021 (07_38)
PRoW GMI 33/4 looking east – Apr. 2021 (07_37)
Chesham Road intervention shaft looking east – Apr. 2021 (07_36)
Chesham Road intervention shaft looking west – Apr. 2021 (07_70)
Chesham Road looking east – Apr. 2021 (07_29)
Chesham Road looking west – Apr. 2021 (07_28)
Chesham Road looking east – Mar. 2021 (07_24)
Chesham Road looking west – Mar. 2021 (07_23)
Chesham Road intervention shaft looking south – Mar. 2021 (07_22)
Chesham Road intervention shaft looking south – Oct. 2020 (07_18)
Chesham Road intervention shaft (07_14)
Chesham Road looking east – Aug. 2020 (07_13)
Chesham Road looking west – Aug. 2020 (07_12)
PRoW GMI 33/4 looking east – Aug. 2020 (07_11)
PRoW GMI 33/4 looking west – Aug. 2020 (07_10)