| 摘要 |
Water drainage elements are used in place of gravel or crushed rock in drainage beds, as around foundations, in sports fields and roof gardens. The elements comprise hollow spherical shells, typically made of thermoplastic material or of metal, having holes for water to flow in and out of the shells. A drainage bed comprising such elements has a higher water-carrying capacity than conventional drain- age beds made with gravel or crushed rock.
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