In this episode, we travel beneath the surface to uncover how water moving silently through soil can make or break some of the world’s biggest structures. We explore why a simple flow of groundwater can topple dams, swallow workers whole, or sink entire highways, and we follow the hidden lines of defense that engineers build to keep these invisible forces under control. From massive gravity dams to deep subway tunnels and city foundations, every wall and barrier relies on secret layers of drains, cutoffs, and clever designs that guide water safely away. It is a quiet battle underground that keeps life above ground safe, stable, and standing strong.

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