Bad glue

From the Boston Globe: "Fast-drying epoxy used in Big Dig let bolts slip over time"

Investigators for the National Transportation Safety Board said today that part of a Big Dig tunnel collapsed a year ago because the wrong epoxy was used to secure the ceiling, allowing bolts to slip or "creep" over time.

Honestly, I can't see the justification to using epoxy at all. If you're going to hold up heavy tiles, a bolt is better (risk of shear) but a cross-connection is best (risk of fracture). But epoxy? You're just crossing your fingers it doesn't deteriorate over time.