How do tetrapod concrete armor units resist displacement by waves?

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Harbors and sea works Yachting harbor at Lorient, France.

Tetrapod concrete armor units resist displacement by waves primarily through their unique geometric design, which allows them to interlock effectively when placed on a breakwater.

The design features four bulbous, pear-shaped legs that project from a central point at angles of 109.5° from one another. This configuration causes the units to knit together so securely that it is nearly impossible to remove a single tetrapod without displacing several others. Furthermore, the spaces, or interstices, created between these interlocking units serve to absorb wave energy, which reduces the force exerted on the structure. Because of this structural stability, tetrapods require significantly less weight than simple cubic blocks to provide the same level of protection against storm conditions.1