British Standard for Concrete Manholes and Inspection Chambers updated
21 Nov 2022
Mark Flavell is the former Technical Director of the CPM Group now working as an Independent Consultant representing MPA Precast on BSI Standards drafting Committee’s.
BS5911 series of standards specifies requirements for concrete drainage products providing both a performance and manufacturing specification. BS5911-1:2021 covers Pipes and the recently published BS5911-3:2022 is for Manholes and Inspection Chambers being complimentary to the relevant European Standards being EN1916 and EN1917 respectively.
This article discusses the principal changes to BS5911-3:2022 as some important updates have been made.
Inspection chambers are generally non man entry chambers less than 1.0m in diameter or length used on drains or sewers. BS5911-4:2002 covered Inspection Chambers but had a lot of duplication with the Manhole Standard. The revised standard has combined the previous Parts 3 and 4 into the new standard. This is also consistent with EN1917 as it covers both Manholes and Inspection Chambers.
Durability is a consideration for specifiers and end users. Any combination of mix design complying with BS8500-1 ‘Concrete’ can be used however MPA Precast members all manufacture to meet AC-4 ground conditions as defined in BRE SD1 ‘Concrete in aggressive ground’ using a DC-4 concrete. This provides a 100 year intended working life. Some units will require consideration of the depth of cover to reinforcement as given in BS8500-1 to achieve the intended working life. MPA Precast members can now demonstrate a 100 year working life for both pipes and manholes.
An important update is the introduction of a higher strength class for manholes. The Water UK publication ‘Design and Construction guidance for foul and surface water sewers’ offered for adoption by Water Companies gives typical details of manhole construction for use in areas subject to vehicle loading. Two options are detailed, one with a 150mm concrete surround used in conjunction with traditional tongue and groove manholes and an alternative that has a wall thickness greater than 125mm not requiring the concrete surround. Prior to the publication of BS5911-3:2022 no method of verification to demonstrate units without a concrete surround were satisfactory when subject to main road loading. Class 1 units are aimed at traditional units with the higher strength class 2 calculated to withstand vehicle loading as in BS EN1992-1 ‘Traffic loads on bridges’. It should be noted that not all Water Companies require a concrete surround to manholes however as the 2 options are detailed in the Code for Adoption, the standard recognises the additional strength offered by the thicker wall units.
Strength classes for Inspection Chambers have been aligned with the "intended place of installation" as defined in BS EN 124:2015 in order that chambers can be readily matched with the manhole covers or inspection chamber covers that they will support. An additional Class being D400 has been introduced which complies with the Design and Construction guidance for foul and surface water sewers Typical inspection chamber detail – Type D. This is for use in areas subject to vehicle loading. Prior to this Inspections Chambers had not been permitted for use in such areas only lighter loading applications.
The strength classes are:
- Class A15 - Areas which are only used by pedestrians and pedal cyclists.
- Class B125 - Pedestrian areas and comparable areas, car parks or car parking decks.
- Class D400 - Carriageways of roads (including pedestrian streets), hard shoulders and parking areas for all types of road vehicles.
In summary, the new revision of BS5911-3:2022 provides specifiers with clear guidance on the intended area of use for both Manholes and Inspection Chambers by alignment with current codes and specifications. Additionally, MPA Precast members complying with the standard can assure customers and specifier’s that their products have an intended working life of 100 years.