"I would be interested to hear if you think that EH have been saying this all along. Or has there been a change in their plans regarding how much original (non-backfill) material will be extracted during tunnelling?"
It seems to me the 'extra tunnelling' has been overstated by some, and the original EH report only ever said extra material (with a figure in cubic meters), might have to removed if it was necessary, in a worse case scenario, in the risk assessment. However it always been EH's declared intent to remove the minimum material necessary to safely backfill the tunnel.
A possible worse case scenario was enlarged upon today, with the example where when the struts of the corroded tunnel supports have to be removed it is possible that a small amount of material where they contact the 'tunnel' might have to be removed as well.
I believe the report is online, someone will have the link I'm sure, but I'll have a looksee too.
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