A correct installation for sewer manholes is, together with the quality and characteristics of the material, one of the key aspects of the final results.
First check that the bed is flat and levelled and remove any protrusion that may damage the waste water manholes. If you need to prepare a bedding or use for the first embankment materials other than those coming from the excavation, remove the materials that may damage the manhole during laying. The bedding surface must be completely smooth and stable between the pipe and the manhole, and in those sections where ground settling is expected, use suitable joints or treat the trench bottom.
As with polyethylene pipes, plastic sewage manholes also require a bedding and backfill with a good degree of compaction, which is easily achieved by using fine-grained loose soil (sand, crushed stone or gravel). This material must also be placed for a radius of 60 cm around the manhole up to ground level. The use of loose soil for backfilling the trench also eliminates swelling and shrinkage phenomena due to changes in water content (groundwater level fluctuations), which are the main cause of deformations in road surfaces.
This laying method, which is also necessary to limit subsidence on the surface surrounding the sewer manhole, can be easily and quickly carried out with the help of simple equipment (compactors). With particularly high loads, concrete can be replaced for the previously planned material, with which the manhole can be lined up to ground level.
For vehicular traffic, we suggest using concrete load distribution plates. These plates, on which the drain covers rest, transfer the overloads caused by vehicle traffic to the sidefill compact ground around the manhole and not directly on it. The load-distributing slab must have a hole slightly larger than the outside diameter of the conical adapter, so that there is never any contact between the slab and the manhole. This method of installation allows these manholes to be used even in areas subject to top category vehicle traffic: the sewer manhole is therefore not directly subject to vertical loads due to traffic.
The standards for polyethylene manholes (EN 13476-1 and EN 13476-2) specify that manhole elevations must have a strength greater than 0.7 kN/m2 for manholes smaller than DN/ID 800 and a strength greater than 2.0 kN/m2 for manholes larger than DN/DI 800. With waste water manholes supplied by Polieco, the elevation can be created with corrugated pipes with a circumferential strength of more than 4 kN/m2 or even more than 8 kN/m2.