The kanji and the word are exactly the same. That means they share meanings as well.
The reading is like the reading of 包み, which means "bundle" or "package." Try to think of an embankment that's made purely from bundles and packages. These 包み (つつみ) are the only thing holding the water in!
The village head decided to bury a human sacrifice in the embankment to prevent it from collapsing.