After that I went to see what's happening in the Crossrail portal; the answer appears to be that they're adding a load of conveyor belts, ducts, etc. which have now filled most of the tunnel entry - that's why they could only connect them after the machines set off. Eventually they will need several MILES of this stuff, which is why it's so massive (and why the infrastructure now stretches about half way to Paddington station). The video I linked to a while ago shows more about how it all works.
At the moment most of the conveyor belt hasn't been fitted, I have no idea what the time frame for this is, except that they seem to be working pretty fast.