Betty and Liva are now enjoying much improved health, after battling for months through hostile surroundings. Such might be the progress report on the two full face earth pressure balance tunnelling machines having achieved 20% of the metro's total 15km of 5.2m diameter running tunnel.
In front lies much of the same variable rock, ranging from abrasive glacial till overburden to hard competent limestone through which much of the route lies.
Between these extremes lie large cobbles within the glacial till and wide bands of hard flint which can occupy 20% of an otherwise limestone face.
But to cope with such variety, the £10M tunnelling trains - supplied by French manufacturer NFM and named after two Danish opera stars - have now had machine heads strengthened.
That the first short 400m section through glacial till, begun in spring last year, took double its programmed three months is attributed largely to constricted cutter head openings and the abrasive sand and gravels which wore away the machine head. All 40 disc cutters on each machine have been replaced, calibration bars removed, increased protection provided around cutter bearings and the head strengthened with steel plates and tungsten studs.
Current driving progress of up to 105m/week - just 7m short of programmed rates - still leaves the tunnelling several months behind schedule.
'We face challenges ahead but have a team of world class engineers to solve them,' says Jefferies.
'I am confident we are winning through.'
The Comet joint venture for the £300M design and build contract is led by Tarmac Construction, now part of demerged company Carillion. The £50M worth of geotechnical work is by the second British partner, Bachy Soletanche, with other JV members French contractor SAE, Austria's Ilbau, Italy's Astaldi and NCC Rasmussen & Schiotz from Denmark. The JV's civils designer is Maunsell & Partners.