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RETENTION OF WATER IN CITIES STORMWATER PROTECTION

The delivery and installation of a system of watertight containers that can be assembled as modules into one or more interconnected watertight basins.

Basins are without membranes and must be able to be installed as finished products into a single unit. The size should ideally be manageable for individuals during installation. The aim is achieve a size of 700 mm x 700 mm x 615 mm and a maximum weight of 21 kg per unit. The tanks must be joinable and water- tight at the connection where the pipe holes are no smaller than a diameter of 500 mm. The basins must be able to be pressure-tested with a maximum of 0.1 bar in accordance with the soil cover layers. Before conducting pressure testing, it must be approved with calculations from the consultant.

The tanks should be able to connect to different pipe dimensions DN 110 mm, DN 160 mm, DN 250 mm, DN 315 mm up to a maximum size of DN 500 mm pipes directly into the basin. After installation, it must be possible to replace individual containers without removing and reinstalling the entire basin. A repair unit must be available to replace defective tanks.

It needs to be possible to access the utility lines beneath the basins in case damage occurs to them.

The basins must be able to withstand a static pressure load of at least 115 kN per m2 and a pressure load of 65 kN on 0.12 m2, corresponding to an axle load of 11 tonnes. The sides must be integrated into the system, where they must be able to withstand a pressure load of at least 100 kN per m2.

The sides should be part of the supporting element. The maximum deflection at the centre of the tank’s surface when buried 40 cm in the roadway (10 cm asphalt and 30 cm stable gravel) is max 1-1.8 mm per m2, which must be documented by an approved and certified research institute.

It must be possible to clean the basins via a pipe hole of at least a diameter of 500 mm in all basins and the water flow must be unobstructed throughout the entire 500 mm diameter of the pipe hole. It must be
possible to separate all channels both horizontally and vertically so that the basin can be divided into several sections with the possibility of installing overflows. All individual channels must be able to be cleaned and TV-in- spected.

The system must be able to incorporate buffer basins and sand traps – with no size restrictions – and still have a sealed basin. It must be possible to install road drains with a minimum 300-litre sand trap and drainage outlets of DN 315 mm and/or DN 425 mm. The basin must be able to contain substrates for rainwater treatment that are shielded from the rest of
the basin system and substrates must be replaceable. If
needed, parts of the basin should be able to drain
water in sections.

For inspection purposes, the basins should be able to accommodate DN 425 mm pipes from the top of the basins. Water brakes and rat barriers should be installable in the system, which will be acces- sible within the tanks.