Yeah, my Christmas anxieties are over! I was finally reduced to drinking NOTHING! in order to let my pills work. It is appropriate that I'm getting nothing on my ad clicks! Now I can be my old nasty self...
When I wrote Niagara Disaster, I was always worried about the lining. How were they going to do it? As we recall, with Niagara rock, we don't want to put in a stiff lining, until the rock has completely relaxed. So now I have found out, since they have started the Over-break Shotcrete Carrier.
This beautiful machine trundles along with a template, and allows them to paste over the over-break with layers of shotcrete. You can see the arc at the top which tells them how far to go. Shotcrete can only be placed in layers, so the 10 foot overbreak might take a long time to fill in. Looks like no room for rockbolts, so they are merely adhering to the existing layers, adding a bit more pressure to fall.
Look at the bottom (invert). This is the final thickness of their baby-smooth concrete lining. All water tunnels need to be smooth, and fairly straight, which keeps the flow laminar. The final lining matches this thickness, and will also be smooth.
And here's the beast for the final lining!
A classic slip form. That is why the shotcrete lining has to be nearly smooth, and this will put in the thick concrete lining. They will most likely be installing a rebar cage, but I don't know.
And now for something completely different.
This is a random shot somewhere in the tunnel, maybe the repaired section. My eye went immediately to the lower left where we see a spall. OOOOhhh! Is it a stress spall?