SAWING A DAM IN HALF (ON PURPOSE)

Summary from the TLDR newsletter

Fontana Dam started showing cracks in 1972, caused by concrete expansion. Engineers decided to give the concrete more room to grow rather than patching cracks as they appeared. They cut a relief slot all through the dam without draining the reservoir or causing any disruptions to the hydropower plant. This post explains how this was achieved. A video showing footage of the procedure is available.