Correct installation is essential to guarantee long life and efficiency of all construction products, therefore including manhole covers. Incorrect installation of the manhole covers, regardless of the material they are made of, can have harmful or even dangerous effects for the integrity of pedestrians and vehicles. The manhole covers must be installed by properly trained and qualified personnel, using appropriate equipment.

The manhole cover must always be in the class appropriate to the place of installation and therefore to the stress to which it will be subject. If in doubt you must use a device of a stronger class than that strictly foreseen. The designer must also choose a size appropriate to the clear opening to guarantee safe access.

Furthermore, before installation, the following indications must be checked:

  • the manhole cover must be appropriately marked with reference to the standard (EN124) and to the certification body which issued the certification marking;
  • the frame must have the same shape as the pit on which it will be placed and the clear opening must be similar to that of the pit;
  • the size of the frame must be less than or equal to the depth of the housing so that, when the job is done, the frame, cover and paving are on the same level. It is preferable that the depth of the housing chamber be 2 to 4 cm higher than the frame to be able to make a concrete bedding which guarantees correct distribution of the loads on the support surface.

As for the choice of material for the bedding, if the road is closed off during installation, cement mortar with characteristic compressive strength (Rck) greater than or equal to 50 N/mm2 can be used, respecting the curing times prescribed by the manufacturer.

If the road needs to be opened to traffic quickly, the manhole covers must be placed on materials for quick hardening installation with the following minimum features:

  • maximum grain size of the aggregates: 4 mm
  • density of fresh mortar; 2300 kg/m3 – 2600 kg/m3
  • volumetric increase in 1 d: + 0.5%
  • workability time: ~15 min
  • compressive strength:
    • after 30 min ˃ 1.5 N/mm2
    • after 1 hour ˃ 8.0 N/mm2
    • after 24 hours ˃ 35.00 N/mm2
    • after 28 days ˃ 50.0 N/mm2
  • characteristic compressive strength of the material at the end of hardening: ˃50.0 N/mm2
  • lasting performance durability and consistency
  • resistance to salt and freezing
  • impermeability to water
  • absence of chlorine

When the level of the manhole cover housing on the pits needs to be raised, a shimming material can be used with a minimum compressive strength of 50 N/mm2, it must have lasting durability and be compatible with the installation materials intended to be used.

Shimming materials are generally made of cast iron, steel or concrete. It is not allowed to use hallow bricks, broken tiles, pieces of wood or plastic or anyhow any type of material which does not provide the necessary strength and durability features.

The contracting company performing the job first of all must make sure that the pit, prefabricated or built on site, is intact and capable of structurally bearing the weight of the manhole cover to be applied.

It is also essential to make sure that the frame and the installation seating on the pit are clean by eliminating any traces of mud, grease or debris. If necessary, the top of the pit could be roughened to improve the hold of the laying material.

The depth of the housing chamber must be made taking account of the height of the devices to be installed, to avoid using shimming materials as much as possible. The width of the housing chamber must be at least 1.6 times the maximum external size of the frame of the device to be installed, so that a consistent and uniform concrete kerb can be made around it.

It is recommended to mix the laying material mechanically and not by hand so that it is homogeneous: the operation must be carried out as quickly as possible and anyhow before quick hardening.

Immediately after applying the laying material, the frame must be positioned promptly at the correct height, centring the clear section of the frame with that of the pit and exerting appropriate pressure on the bedding to guarantee a firm grip, making sure that no internal part of the frame overhangs the pit. The frame must not be positioned directly on the top of the pit.

The frame must be positioned on the bedding so that its bearing surface is appropriately supported by the top of the pit/chamber. When installing the cover in the presence of heavy and/or frequent vehicular traffic, it is recommended to anchor the manhole cover frame to the concrete slab or wall of the underlying concrete pit, positioning the fastener plugs in the specific circular slots in the frame. Furthermore the frame must be positioned at road level using appropriate reference points and so that it is level with the surrounding surface.

Make sure there are no empty spaces between the manhole covers and pit; pay special attention when applying the laying material near the cover seating so that residual material cannot deposit. It is also necessary to make sure that the laying material covers the flanges of the frame with at least a 1 cm width and comes out of any holes or slots on the frame, providing a perfect grip.

Beddings thicker than 4 cm should be applied at two different moments: the first layer should be 2 to 4 cm thick, while the following layer should only be applied after having placed suitable primer material in between. Make sure to leave sufficient residual thickness for the finish of the road surface. The exposed surfaces of the bedding, both inside and outside the frame, must be smooth and made even.

The manhole covers must be inserted carefully into the frame only after the material has a sufficient grip and compressive strength and only after a careful check and cleaning of the support surface of the seal and of the seating of the frame where the cover must be inserted.

The finish filling around the manhole cover must be carried out after at least 3 hours with the same laying material, leaving a layer of at least 3 cm to allow the finish of the road surface by laying asphalt. Make sure no compacting devices pass over the manhole cover to avoid damaging the bedding/frame/cover system. The installation must not be subject to any type of stress until the bedding material has reached sufficient strength. After installation, the frame and cover/grating must be level with the road surface.

Before opening the area where the manhole cover is located to traffic, the curing times supplied by the manufacturer of the product used must be respected: if there are no different indications, it is necessary to wait at least 72 hours.

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