Recommended Site Work Practice
FP McCann Manhole Installation
Handling & Installing Manholes
- Time and place of off-loading should be agreed before the units arrive at site. The contractor should provide suitable equipment for off-loading. For safety, all chamber sections are delivered chimney fashion.
- Off-loading should take place at the nearest hard road to the point of installation. When off-loaded, units should never be stored on their side (on the roll), but should always be laid in the "as installed" position.
- Carefully inspect units during off-loading to verify that products are undamaged and comply with order placed. Note any discrepancies on the delivery docket.
To ensure that the manhole structure is vertical, accurate levelling of the formation or the in-situ concrete foundation is essential. Tongue and groove joints should be installed with the socket facing upward. Manhole sections fitted with double steps can be used in any depth configuration. However, it is recommended that the deepest section of manhole units should be used whenever possible in order to minimise the number of joints and costs. Precast cover slabs can be laid directly onto the shaft or chamber rings.
To allow for any differential settlement between manhole and pipeline, a flexible joint incorporating short length rocker pipes should be constructed as close as possible to the outside of the manhole or the concrete surround if used. Extra care must be taken to ensure that joints are properly made.
Precast manhole components are provided with joints formed within the wall section. These are sealed with cement / sand mortar or with proprietary mastic sealants. Precast concrete manhole units, well jointed, provide an adequate seal under normal conditions.
In-situ concrete surround to precast concrete manholes is not necessary as a well constructed precast manhole is a strong durable structure with its own inherent strength and would only require a surround for exceptional structural reasons. However under some specifications a concrete surround is required where the depth from ground level to the base of the concrete chamber rings, exceeds 4.5m. Such surround should be of 150mm thickness. Backfilling should take place as each precast manhole section is placed. It must be brought up evenly and compacted around the manhole to prevent displacement.
It is generally unnecessary to apply water tests to manholes. In working conditions manholes are not normally full of water. Prevention of infiltration is of more relevance than ex-filtration. If infiltration does occur it can be seen and remedied by sealing using an appropriate method.
Note: When handling precast products on site it is recommended that the contractor has the correct lifting equipment in place and adheres to the relevant lifting guidelines and standards.