If you want to know how to do one yourself -
there's more details here. It does seem an awfully complicated and expensive way of doing it. I wonder if the driver was to avoid more than a day or two of main line closure, in which case that mischievous virus has pretty much rendered that pointless.
It needed a 10 day closure of the 3 lines crossing the location. They kept a skeleton service going using the Stamford lines and the single track ECML connection just north of the site. But I?ve been wondering if they could have used a different build sequence entirely, ie by moving the ECML over to the west while the built half the underpass, and then moving the tracks back to build the down ramp and remainder of the box.
Maybe though, a track diversion with resulting speed restrictions over a long period is enough to wreck the entire timetable...
On another point though, I think the fully engineered launch way, and the twin pilot tunnels through the embankment, containing guide rails, made it a significantly different process to the bridge failure at Gipsy Patch Lane.
Paul