to crumble down; to tumble down; to fall in
古い壁が崩れ落ちた。
The old wall crumbled down.
建物が今も崩れ落ちている。
The building is still crumbling.
地震で崩れ落ちるような古い建物は補強が必要だ。
Old buildings that could crumble in an earthquake need reinforcing.