HS2: more sinkholes open up in the Chilterns

Both tunnel boring machines (TBM) are now nearing the end of their journey beneath 16km of the Chilterns. On Friday 19 February, the first TBM, Florence, had 36m further to go to complete this journey. Unfortunately, even at this late stage we are receiving reports of further sinkholes appearing above the tunnel – bringing the total number, that we are aware of, to four.

Geology experts highlighted the challenges presented long before tunnelling commenced, though the HS2 contractors have remained confident that their tunnel design and construction technique remains safe. Along with others, Chilterns Conservation Board remains concerned that instability in the chalk above and around the tunnels might still present yet unknown impacts on water flowing through the chalk aquifer and on future ground stability above the tunnels.

While there will no doubt be significant celebrations and relief when the TBMs emerge from the north portal site near South Heath, questions over ground stability are likely to remain.

*Featured image shows the sinkhole that opened up near Shardeloes Lake in May 2023.