In fact, big surprises were rare.
For a project this complex, a lot of preparation ( "de-risking" in the jargon) is needed before private contractors can be confident they won't encounter big obstacles, and can price a bid sensibly.
Once contracts were awarded, it was up to project managers to keep to the timetable.
Unexpected delays, such as slow delivery of fittings, are managed in three ways, says Mujahid Khalid, who is in charge at Farringdon.
A “float” of unallocated time can be drawn upon; other tasks can be brought forward; and, as a last resort, the number of shifts can be increased.
The ground has to be prepared for the six floors of offices and shops to be built over the new station.
Such “over-site” developments are part of the project's financing.
Indeed London's businesses are stumping up ￡4.1bn in a variety of ways for Crossrail.
With hindsight, the sponsors might have considered charging for tours of the Farringdon site by visitors from cities seeking lessons for their own metro systems.
It would not be the only unorthodox initiative.
The tunnels needed eight bespoke boring machines.
Four dug their way back to surface and were sold back to Herrenknecht, the German manufacturer.
Four (two running eastward and two westward) reached the ends of their lines beneath Farringdon.
Stripped of valuable kit for recycling, the remains were left there: strange skeletons for 28th-century archaeologists to pore over.