Carefully selecting a route which couldn't possibly have any issues would prove nothing.
Which is why I 'carefully selected' the 3 miles to Metrocentre. Dunston and Teams (in Gateshead) are littered with ex-collieries. The Metrocentre itself is partly built on the old mineral railway sidings! Same story all the way along the Tyne Valley across to Hexham.
The 3 miles to Metrocentre Includes a 110m tunnel (for the grade separated junction where the slow lines diverge from the ECML); for good measure a few overbridges for renewal or track lowering can be included too.
Arguably removing 75mph diesel stopping services from the 125mph ECML is a priority an order of magnitude higher than an infill scheme which will use bimodes on the busy electrified section anyway (Lostock-Wigan).
Lostock to Wigan is of course in a mining area so could experience some of the same geology problems of Preston to Manchester
Exactly, where lessons have been learnt and new solutions can be implemented from the get-go.
The bit between Hindley and Ince is practically as bad as it gets in terms of the sheer amount of ex-mining activity; worse than the Bolton line. Although NWEP 2b was through similar conditions near Wigan (around Ince Moss Junction). The Coal Authority even have one of their mine water purification systems not far from Hindley station.