I’d never heard of this method of tunnel construction. Odysseus, who first posted it at his blog By Other Means, called it ‘Grown Up Lego‘. That’s not a bad description.
I wonder if the truck has to be left in that configuration permanently, or whether they can dismount or uncouple the tunnel-shaped thingamajig to use the truck for normal work, then reattach it when it’s needed once more? Also, can the same technique be used for larger or smaller tunnels, or is it basically limited to what can be fitted to the truck? If anyone knows the answers, please tell us in Comments.