It's never been clear to me how the segments are delivered to the machine and how they're handled when they get there. All the videos and pictures I've seen show the machine is a really tight packed space that doesn't seem big enough to store/manoeuvre many more than a few tunnel segments. I guess it must be a "just in time" kind of thing in terms of delivery to the machine.
A complete ring is transported from the segment storage compound near the tunnel mouth to the head of the TBM on a ‘Multi Service Vehicle’. This is a purpose built, double ended* vehicle that holds segments, but can also transport the tunnellers, and the other equipment to and from the TBM (takes in pipesork to extend the slurry system, ducting for air, cabling for power, spare parts, and of course all the non-tunnelling waste generated.
*double ended in that it can be driven from either end; no room to turn in the tunnel of course.
I don’t know what the speed limit for these vehicles in the tunnel is, but if it is, say, 20mph it will be taking half an hour to get each way when the tunnel is nearly finished.
For 15m per day pace that requires 3.75 deliveries from the tunnel service vehicle (1 ring worth of segments at time) so @ 6 hours per return trip (1 vehicle per tunnel) shouldn't be pushing it, even allowing a very generous for 1 hour loading or unloading at each end still only needs the vehicles to move at brisk walking pace at the far end of the tunnel.
I thought each ring was 2m worth of tunnel (7 segments, 28 m circumference of tunnel, 4mx2m in size).
7.5 deliveries a day, but I agree 3 hours should be enough. But that extra hour or so for the transport will make it tighter.