It sounds like by default the slag is in the form of ash. That's actually the main advantage I was thinking of; current long tunnels require mixing it with wate

It sounds like by default the slag is in the form of ash. That's actually the main advantage I was thinking of; current long tunnels require mixing it with water to make muck and transporting it all the way back out. I don't know if they ever lift it out via vertical or angled dumping tubes? Seems like a pain. And then getting the muck out interferes with getting the tunnel lining in. The muck is far from homogeneous, so it's difficult to deal with.