"One rumor going around is that when the construction crews drilling the holes for the tie-backs ran into rebar, they stopped drilling and cut the bolts short.
"
Wouldn't surprise me at all. Neither would shorting the cement content in the concrete used in the panels. I've seen enough of that kind of nonsense in construction to make me wary of most large projects. The temptation to cut costs by contractors is just too much for some to resist.
I still maintain, though, that it is the design that is at fault here. Any design that suspends concrete panels like this one is going to suffer failures at some point. It's inevitable. A small water leak will corrode fasteners faster and anyone would believe, and can weaken the concrete itself.
So, when a panel falls on a passing vehicle...well...we've seen what happens.
I see no alternative at this point, but to remove the entire lot of the panels. Imagine the additional cost. Someone needs some prison time over this incident.
. . . especially when you drill through the rebar in the ceiling of the tunnel . . .
Yes. And even if you're going to go with a ceiling like this, the slabs should have been resting on an I-beam frame with I-beams on the sides to transfer the load to the ground.
Someone on the other thread said that the airspace above the ceiling was supposed to be used to vent fumes in case of a tunnel fire. But I can think of many other safer and less expensive ways to do that.