IPC 2013 : E03B 3/24 : formed of loose materials, e.g. gravel.

IPC2013 > E > E03 > E03B > E03B 3/00 > E03B 3/24[5] > formed of loose materials, e.g. gravel.
Notes[t] E01 - E06: BUILDING
E SECTION E — FIXED CONSTRUCTIONS.
E03 WATER SUPPLY; SEWERAGE.
E03B INSTALLATIONS OR METHODS FOR OBTAINING, COLLECTING, OR DISTRIBUTING WATER (drilling wells, obtaining fluids in general from wells E21B; pipe-line systems in general F17D).
E03B 3/00 Methods or installations for obtaining or collecting drinking water or tap water (treatment of water C02F).
E03B 3/24 · · · · · formed of loose materials, e.g. gravel.