Panama

When the Panama Canal was expanded, the entire project ran into trouble because of sand.

Local basalt, a hard volcanic rock, was crushed to make the concrete. But hidden inside the rock were clay minerals. When they crushed the stone, it produced far more very fine sand than expected, too fine to meet the requirements for the concrete.

Engineers found themselves investigating a geological mystery in the middle of construction: why rock that had passed the tests was suddenly producing the wrong kind of sand.

The problem became a major cause of delays and substantial cost overruns before the new locks finally opened.