cave in (
http://definr.com/cave in)
n : the sudden collapse of something into a hollow beneath it
[syn:
subsidence]
v : break down, literally or metaphorically; "The wall
collapsed"; "The business collapsed"; "The dam broke";
"The roof collapsed"; "The wall gave in"; "The roof
finally gave under the weight of the ice" [syn:
collapse,
fall in,
give,
give way,
break,
founder]