The core of the heap (zone 1): Clay (clay)The cover of the filter (zone 2): sand (sand) and gravel (gravel)Random stone heaps (zone 3): RandomThe cover of Rip-rap (zone 4): stone (rock)
Heaps core (zone 1): Clay (clay) Fill the filter (zone 2): sand (sand) and gravel (gravel) heap Random stone (zone 3): Random heap Rip-rap (zone 4): rock (rock)