With regards to the recent news story HS2 plans to reduce ground risk cost described as “carnage”, perhaps HS2 costs wouldn’t be spiralling out of control, with the need to reduce ground risk cost, if way back before the 2013 route announcement, HS2 had followed their own route selection process
This required identification of mineral extraction, mining and other geological risks. HS2 admit they didn’t do in Cheshire: “It is worth noting that considerations of salt and other geological risks were not explicitly considered at this early stage of option development”. HS2 Ltd Document: Consultation Route Technical Note – C320 Contract – Cheshire Salt Area Review HS2 Document Number: C320-AEC-CV-NOT-220-000003.
As a consequence, HS2 and its advisors failed to identify on, beside and under the HS2 proposed route, the presence of former and active salt subsidence, past and active rock salt mining, active salt solution mining brine wells and active strategic gas storage in salt cavities.
Here’s a challenge for HS2: how to reduce ground risk cost for the unknown salt solution cavities beneath Cheshire’s Salt District, products of at least 11,000 years of natural salt solution, 2000 years of continuous brine extraction and over 200 years of wild brine pumping. With a legacy of cavities and broken ground without known, recorded boundaries and locations. Salt mines (dry rock salt and salt solution mining) have mine plans - not so for uncontrolled wild brine pumping and natural salt solution.
Cheshire throws down the gauntlet to HS2: the challenging and costly geotechnical ground conditions of the salt district are ”not unforeseen circumstances” that will need extra funding during construction. These are ”foreseen but known to be unknown ground conditions’”that does need HS2 to do some really meaningful up front Geotechnical Baseline Reports to reduce ground risk let alone ground risk cost “carnage”. Perhaps HS2 should have done such GBRs pre 2013?
Cheshire resident and former mining geologist and lecturer in applied geology and geophysics (retired)