Proposal for tender text


Proposal for tender text

The volume of the retarding basin must be established with BIO-BLOK® 80 HD GF or similar net tubing elements. The elements must be made of welded vertical net tubes produced in polyethylene with a modular size (W x L x H) of approx. 54 x 54 x 55cm. The elements must be able to resist an even, vertical load of a maximum of 15 tonnes per m2 and the percentage of hollow space must be approx. 95%.

The inlet pipe to the basin must be a Ø 400mm PVC pipe where a Ø 100mm hole has been drilled every 0.5m into the top of the pipe. The top of the inlet pipe must be placed in the bottom of the basin. Out of consideration for the water’s erosion and the basin’s foundation, the inlet pipe must be recast. A geotextile is then laid down in which holes can be made.

The basin must be wrapped in geotextile (fibre cloth). A geotextile, such as Typar SF27, can be used for the bottom of the basin. However, a sturdier geotextile such as Typar SF56 should be used on the top and sides of the basin. All sides of the basin including the top must be filled with at least 20cm of base gravel or equivalent.

The net tubing elements must be stacked using stacking pipes and assembled using stainless steel clips to ensure good stability in the basin. At least two stainless steel clips must be used on each side and put together.

For assembling the elements in the layer structure, use two stacking pipes per net element in the external elements of the basin. In all other net tubing elements, use one stacking pipe per element.

Sand must be filled in and the bottom built up so that the requirements of the construction going above are fulfilled, although the filling etc. must be compressed to a minimum of 95% standard Proctor (Isotope method).

The basin must be ventilated at the top of the closest inlet using at least one Ø 110mm PVC pipe.