Riprap

Riprap (in North American English), also known as rip rap, rip-rap, shot rock, rock armour (in British English) or rubble, is human-placed rock or other material used to protect shoreline structures against scour and water, wave, or ice erosion.[1][2][3] Ripraps are used to armor shorelines, streambeds, bridge abutments, foundational infrastructure supports and other shoreline structures against erosion.[1][2][3] Common rock types used include granite and modular concrete blocks.[4][5] Rubble from building and paving demolition is sometimes used,[3][6] as well as specifically designed structures called tetrapods.

Look up riprap in Wiktionary, the free dictionary.

Riprap is also used underwater to cap immersed tubes sunken on the seabed to be joined into an undersea tunnel.^{[citation needed]}