As with all plastic structures, installation and backfilling of these manholes/draw-boxes both form an integral part of the structure. Bad/inadequate installation practice may lead to failure.
A stone free bedding (underlayer) of minimum 50mm is required. Quarry sand is suggested.
Backfilling (reinstatement) to paving level should be competed with stone free (-6mm) material. This should be layered 50 – 75mm
at a time, and tamped to required compaction. Stabilisation of the backfill material with the addition of 5% cement is recommended, ensuring stability of the construction/assembly.
These are small units, and mechanical tamping is not recommended.