Big Dig ceiling collapse
Boston.com
Engineers entered tunnel. The section that fell is over their heads about 50 yards down.
Engineers entered the tunnel. The section that fell is over their heads about 50 yards down.

Amorello said he's confident that the 200-foot section is the only area of the Big Dig project where the type of tiebacks that failed were used.
(Globe Staff Photo / George Rizer)