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The revised standard for structural design of buried pipelines will soon bring methods into line with contemporary design practice. Marshalls CPM’s director of technical & engineering, Mark Flavell, who represented BPDA on the drafting committee, explains the importance of this update.

At the end of November 2019 a revised version of British Standard BS 9295:2010 Guide to the structural design of buried pipelines will be released. The new BSI document will include all relevant design information for all types of buried pipelines, which was previously split across two different standards.

Standards for buried pipelines make it possible to demonstrate that a pipeline is structurally sound, especially when it passes under a highway or motorway. Adopting authorities require uniform documentation, that is understood by all parties, to confirm the infrastructure is fit for purpose and can take the traffic load.

Currently BS EN 1295-1:1997 details the UK nationally established method of design for rigid concrete pipelines, while BS 9295:2010 gives further information on the structural design of buried pipelines under various conditions of loading using the established UK method.

When BS EN 1295-1 came up for its five-year review, BSI’s Management Committee for Wastewater Standards gave a mandate to revise and it was decided to withdraw the method of design from this standard and revise BS 9295 to include all the detailed design method together with the guidance on its use.

BS 9295:2019 will be the key standard for anyone in the construction industry that designs or builds drains, sewage systems and underground pipes. Revision of the standard has provided a suitable opportunity to review various shortcomings in current UK design methods which have arisen due to changes in the nature of pipelines over the period since those methods were originally published. In the case of concrete pipelines, this is over 50 years.

The revised standard consolidates and updates the various documents that together describe the UK method and brings practice into line with contemporary design methods. Alignment with the European Eurocode standards for structural design was also considered wherever practical.

The timing of the publication of the revised standard is of particular importance because the HA 40/01 Determination of pipe and bedding combinations for drainage works from the Design Manual for Roads and Bridges (DMRB) is also being revised and will be redrafted around BS 9295:2019.

One of the principal changes to the documentation will be to ensure that traffic loading used is consistent with British and European standard BS EN 1991-2 Traffic Loads on Bridges. This will align pipeline design with design requirements for all other buried structures. It is also consistent with the vertical test loads for manhole cover slabs as specified in BS 5911-3:2014.

The revised standard places more emphasis on consideration of the wide-trench formula for pipe design. Using wide-trench principles increases potential load on pipelines, however higher bedding factors have been introduced for designs using wide-trench design. Narrow-trench design is still permissible where the designer has sufficient knowledge of the installation conditions to make a well-informed decision on trench width.

Narrow trench design has been used by the Industry for many years without any concerns being raised regarding the structural integrity of concrete pipelines. This demonstrates the robust structure of concrete pipes and the conservative nature of design methods. However, the standard steers designers towards wide-trench as ideally a maximum permissible trench-width should be stated.

Two new tables are included in the revised standard – one for updated bedding factors and one detailing permitted installation cover depths for both narrow and wide trench applications.

A limit state design (LSD) method is introduced for concrete pipelines which means they can be designed to withstand all actions likely to occur during their design life and remain fit-for- use, with an appropriate level of reliability for each limit state.

A limit state is a condition beyond which a structure no longer fulfils the relevant design criteria. The condition may refer to loading or other actions on the structure, while the criteria refer to structural integrity, durability or other design requirements.

The procedure requires both an ‘ultimate’ and ‘serviceability’ bedding factor to be calculated and appropriate bedding factor assigned. All Eurocode European standards are based on the LSD concept in conjunction with a partial safety factor method.

Finally, an annex to the section gives typical examples of pipeline designs covering various design situations. This includes a comparison of wide-trench and narrow-trench design for the same diameter pipe and reinforced and unreinforced scenarios.

In summary, the new standard brings methods into line with current design practice while aligning with Eurocodes, introducing LSD and making trench-width a primary consideration. With release of the revised DMRB in 2020, the UK will have a joined-up contemporary approach to buried pipeline design.

Structural Design Calculator update planned

BPDA plans to bring its own Structural Design Calculator app for pipe design into line with the new standard in early 2020. The Calculator, which is available from any app store, simplifies concrete pipeline design calculations.

It offers all the basic values including external design loads and bedding factors and takes into account the pipe crushing strength. It then offers advice on what type of bedding to use. The calculated load, which is the total load a concrete pipe in a trench is required to sustain, is used in the design formula.


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British Precast, the federation trade body which includes BPDA and a number of other precast concrete product associations, issued a Press Release on Monday 2nd September about precast drainage products placed in the UK market without any visible proof of conformity to relevant provisions of British standards or sufficient Declaration of Performance as required by relevant European Standards. The press release can be found here:

The products in question include manhole rings, seating rings and gully risers. British Precast found units of these products without any visible proof of conformity to BS 5911-3 and/ or sufficient Declaration of Performance in accordance with EN 1917 and the Construction Products Regulation (CPR). Proof of conformity to any standard, whether European or British, can only be assured through some form of third-party certification such as BSI’s own Kitemark or an equivalent certification system. British Precast feels that the precast drainage sector has a responsibility to demonstrate that their products are safe and fit for purpose. Clients of the sector too have a requirement to ensure that the products they use meet their specification and whatever industry standard they need to comply to (e.g. Sewers for Adoption, CESWI, etc).

Below, we answer some of the main questions associated with that press release:

What are the main standards for precast pipeline products?

The main European standards for precast concrete pipeline products are EN 1916 and EN 1917:

  • EN 1916: Covers concrete pipes and fittings
  • EN 1917: Covers concrete manholes and inspection chambers

There are also complementary national British Standards for these products, which offer more details on geometrical requirements, concrete mix, structural characteristics and production specifications. The main standards include:

  • BS 5911-1: Covers concrete pipes and ancillary products
  • BS 5911-3: Covers concrete manholes, soakaways and ancillary products such as cover slabs, seating rings and corbels.
  • BS 5911-4: Covers inspection chambers
  • BS 5911-6: Covers gullies.

Not all precast drainage products conforming to EN 1916/ EN 1917 will automatically conform to BS 5911-1/ 5911-3. For example, concrete pipes can be manufactured to Strength Class 90 and seating rings can be produced with DC-1 concrete exposure class. These may comply to EN 1916/ EN 1917 and could be in use in a number of countries across Europe. But pipes and seating rings with such specifications cannot be manufactured under BS 5911: BS 5911-1 is restricted to Class 120 pipes and BS 5911-3 only makes reference to concrete manufactured to design chemical specifications higher than DC-1.

What do industry standards say?

  • Sewers for Adoption: SfA notes that ‘Precast concrete (in reference to Manholes) shall comply with the relevant provisions of BS EN 1917 and BS 5911-3” and “Precast concrete slabs and cover frame seating rings shall comply with the relevant provisions of BS EN 1917 and BS 5911-3”. SfA also notes that “Additional quality assurance requirements, including Third Party Certification, may be sought by the Undertaker” and offers Kitemarking as an example.
  • CESWI (7 th edition): Clause 2.98 notes that “Precast concrete slabs and cover frame seating rings shall comply with the relevant provisions of BS EN 1917 and BS 5911-3”. Clause 2.101 also noted that “Precast concrete manhole and soakaway units of circular cross-section shall comply with the relevant provisions of BS EN 1917 and BS 5911-3”.
  • Highway England’s Manual of Contract Documents for Highways (Vol 1. Series 500): Clause 507 (sub-clauses 4 and 5) note that precast chambers, cover slabs and inverts “shall comply with BS 5911-3”.

Is it legal to produce and sell such products?

For a number of regulated construction products, covered by harmonised European product standards, CE Marking is mandatory. The Construction Products Regulation (CPR) includes requirements for some construction products to have CE marking and to be accompanied by a declaration of performance (DoP) and other information if it is to be placed on the market in the European Economic Area. Most precast concrete pipeline products used and sold in the UK (pipes, manholes, cover slabs, benching rings and other ancillary products) are covered by this requirement. Conformity to British standard BS 5911-3 is not a legal requirement. However, in projects where some industry standards such as ‘Sewers for Adoption’ and CESWI form part of a water company or public authority contract, there might be a restriction set in specification for such precast drainage products to conform to relevant provisions of BS 5911 (Parts 1 to 6) and be third party verified in accordance with the requirements of that standard.

What is the main message?

The main message from the press release is as follows:

  • Manufacturers of precast drainage products need to ensure that their Declarations of Performance and CE Marks are in order and made visibly available, either on products or the manufacturer’s website. This is a legal requirement that manufacturers need to achieve in order to protect users, third parties and comply with the CPR.
  • Manufacturers and merchants are encouraged to seek third party certification if they intend to sell to specific markets where an undertaker (under Sewers for Adoption or any other industry standard) may require such certification as proof of conformity to relevant provisions of BS 5911-3. The Kitemark is one example of such certification.
  • Undertakers and clients need to understand that not all precast concrete drainage products are the same. In cases where no third-party verification is available, more scrutiny may be needed to ensure that a precast drainage product actually meet the project’s specification.


Posted by & filed under Pipes & Manholes.

Advances in production techniques for precast manholes offer multiple advantages for the construction sector. Innovations championed by BPDA

members mean manhole installation can be completed in about an hour, with a much higher success rate when compared with traditional techniques.

Precast manhole systems are easier to install, but they also improve onsite safety and raise the bar on quality and performance as well as lowering costs and reducing waste to landfill. To help contractors deliver best practice on-site, BPDA has now produced a handy guide to installation.

The Pocket Guide to Installing Concrete Manholes can be downloaded from the BPDA website as a PDF or is available as a printed document. It lists seven simple steps to successful precast manhole installation (with minimum 125mm wall thickness) and the full version can be found at


Design flexibility

Precast concrete manhole systems are suitable for a wide-range of pipe connections and can be retrofitted without complete replacement of the chamber. The systems comprise a precast concrete base unit with channel and benching and predetermined combinations of flexible and watertight inlet(s) and outlet. Base units and chamber rings are made with thick strong walls and lifting points, eliminating the need for a concrete or granular surround unless specifically required by the client. High-performance seals and extra-thick chamber walls ensure long-term watertightness and durability. The excavation is backfilled sooner than with traditional techniques, minimising the health and safety risks associated with open excavations, and there is less need for work in confined spaces, which also lessens risk to workers. By reducing project time, overall costs are also brought down.

Sourcing constituent parts from local suppliers and a rise in the use of recycled materials keeps embodied carbon impact to a minimum. Production techniques for precast manhole systems continue to advance and the use of modern logistics ensures excellent and consistent product quality and reliable service.

In summary the seven steps are:

  1. Safety

Safety must always be the first priority for any construction project and all site activities must be preceded by an appropriate risk assessment. Typical activities include vehicle offloading, movement of components, excavation, backfilling and the lifting and positioning of components.

  1. Preparation

Excavate a trench of appropriate dimensions to accommodate the manhole structure. The trench must allow sufficient working space outside the chamber for access and backfilling to the required specification, taking into account the ground conditions, depth of excavation and any other relevant factors. The heights of the manhole components supplied by the manufacturers are nominal, so it is beneficial to measure the units prior to installation in order to assist with obtaining the required height of the completed chamber.

  1. Installing the precast manhole base

Prior to lowering into the trench, the precast base unit may be pre-fitted with a lubricated outlet if required. A plastomeric sealing strip/elastomeric seal is used to form a waterproof joint between units. It may be fitted before lifting into position or after

each unit has been individually placed. Concrete to concrete contact between units must be avoided.


Place the base unit onto the prepared granular bed and mate the stub pipe with the installed outlet pipe. Check the base position for alignment, level and inverts. Note that precast bases have an inbuilt fall across the main channel and can be installed level.

  1. Fitting the chamber rings

Make sure that the joints are clean and free from foreign objects before fitting the next chamber ring unit. The plastomeric sealing strip/elastomeric seal should already be in place on the installed unit and ready to receive the next chamber ring unit. Repeat with further ring units until the chamber has been constructed to the required height. Ensure that the steps are correctly aligned.

  1. Fitting the cover slab

Place the cover slab directly on the last chamber ring with the access opening lined-up with the steps. Apply slight pressure onto the cover slab using suitable protection, such as timber, to seal the chamber.

  1. Backfilling

When using wide-wall precast concrete manhole chamber rings, the excavated soil can be returned as backfill unless an alternative arrangement is specified by the client. Compact the backfill soil as specified in the design.

  1. Operation and maintenance

Precast concrete manhole base systems are strong and durable and eliminate the risk of inconsistent quality from site-based operations. They are designed to remain watertight and maintain their structural integrity for over 120 years.



Fact Zone: Concrete Manholes

Up until the 2000s concrete manhole construction has required manhole bases to be constructed onsite from ready-mixed concrete. This required the channels, connections and benching to be constructed in confined spaces with works often carried out in wet and hostile conditions. Additional external contractors were required to supply and pour the concrete and the process for each installation would take several hours due to routine logistical and operational challenges. Furthermore, construction was not always successful. In 2011, a revision of Part 3 of BS 5911, the main standard for precast concrete manholes, introduced a new type of precast manhole system. This comprised a factory-made precast base with elastomeric or plastomeric seals on all joints and connections to ensure permanent watertightness.





Posted by & filed under Pipes & Manholes.

A report into Sweden’s water and wastewater networks anticipates a long-life for the next generation of pipes. The authors of Sustainable water and wastewater pipe systems of the future, which has been published by the Swedish Water & Wastewater Association (SWWA), argue that the networks currently being installed should have an operational life of at least 100 years and that pipes laid from 2020 should have an operational lifetime of 100-150 years.


The report also argues that the current renewal rate needs to increase by 40% to maintain the current condition of the network. However, when renewal is carried out, it should be done to such a standard that the new pipes have an average operational lifetime of 100-150 years.


Concrete pipes account for 69% of the waste- and storm water pipelines in four of the main water utilities – NSVA (six southern municipalities), Kretslopp och vatten (Gothenburg), VA Syd (Malmö) and Höganäs. This is representative of the country as a whole, though some have been rehabilitated or replaced in the 10 years since this figure was calculated.


A survey in Malmö found that many concrete pipes are still operating successfully 100 years after installation. Unreinforced concrete pipes manufactured in Sweden today are generally 150-1000mm diameter, with the larger reinforced concrete pipes coming in at 400-3000mm. The main method for condition assessment of gravity sewer lines is CCTV, particularly for assessment of pre-stressed steel reinforcement pipes.


Concrete pipes laid in the 1940s generally have a shorter life of 50-100 years due to the shortage of cement during the Second World War and its substitution with finely ground limestone filler. They currently require replacement. It was during the 1960s and 1970s that most concrete pipes were installed and, given a pipe-life of 100 years, a major replacement programme will be required around 2050.


The various causes of deterioration of underground concrete pipes are already fairly well known. Sulphuric acid attacks from the hydrogen sulphide (H2S) in sewage can reduce the thickness of concrete, especially where the sewage flow slows down or becomes stationary.


Increasing durability

The durability of concrete pipes can be improved in a number of ways and cured-in-place pipe (CIPP) lining is common in Sweden. Resistance to acid and sulphate degradation can be improved by mixing a number of alternative binding agents into the concrete, particularly a ground granulated blast-furnace slag (GGBS) such as Alfarör, which uses a 15% slag mix and fly ash.


Some of the older pipes in Sweden are believed to have been made using 100% Portland cement. In the UK almost all concrete pipes are manufactured to exposure class DC-4, which includes 30% fly ash or GGBS to 70% Portland cement.


Other additives, such as limestone filler or polymers, can be effective, as can a number of surface treatment methods including internal centrifugal spraying.


Recent innovations include mixing bactericidal additives, such as a cationic polymer, into fresh concrete. The polymer is particularly effective in binding and rendering H2S bacteria, while avoiding harm to other bacteria. It has been used successfully in North America since 1996 and became available to the Swedish market in 2010.


In parts of the world where bacterially-induced H2S formation appears as a result of exposure to an optimum temperature of around 30°C, calcium aluminate cements such as Ciment Fondu Lafarge are used. They have greater chemical resistance than most Portland cement and are used for both the manufacture of concrete pipes and also as cement mortar insulation.


Further Research

The report’s authors recommend that more research is undertaken on how to prevent, control and forecast the degradation of concrete in ageing sewer pipe systems. Particular regard needs to be paid to developing innovative non-destructive methods for condition assessment and online surveying, which can provide valuable data to support maintenance planning and prevent unexpected disruption to operations.


New non-destructive techniques and sensors need to be developed, along with forecasting tools that can enable proactive maintenance and minimise leaks, bursts and network failure. For concrete sewerage this involves the generation of a model for pipe degradation based on the key factors of H2S, temperature, soil movement, reinforcement and corrosion.


Selected information translated from the SWWA’s report The Sustainable Water Management System of the Future (Framtidens hållbara VA-ledningssystem, 2018). Authors: Helena Mårtensson, Annika Malm, Bror Sederholm Jan-Henrik Sällström, Jan Trägårdh (original article published at the Summer issue of the BPDA Newsletter).


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BPDA has just published a new site guide on the installation of precast base manholes. The guide identifies seven basic steps needed for correct, easy and safe installation.

Precast base manholes have been in use in the UK for well over 10 years. In 2011, the main British standard for concrete manholes, BS 5911-3, was revised to allow such manhole solutions to be Kitemarked and more widely specified in the UK. The new system reduces installation time and cost significantly: what used to take several hours, involving sub-contractors and wet trades on site, now takes approximately one hour and would not involve more than a handful of operatives.

BPDA has put together an operative short site pocket guide to explain the installation process: From trench excavation and ground preparation, to the installation of different manhole units and final backfilling. The guide was set up in an ‘endorsement fold’ format to ease use on site.

A PDF copy of the new pocket guide can be found at the BPDA downloads page, or to request a hard copy please complete an Online Request Form.

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BPDA has just published a newly revised version of the precast concrete drainage sector’s “complete technical design guide”. Since our last issue of the guide, a number of standards, design methodologies and guidance documents were published. Moreover, feedback and enquiries we received over the last two years made us think about how to expand the content to address new areas. Here is a summary of the new sections we added to the precast drainage technical guide:


Chemical ground condition and the concrete exposure class

We added some information about the design life of precast drainage products and how a 100+ years can be achieved by using a DC-4 ‘Design Chemical’ exposure class. Our Technical Guide never used to refer to this in the past as we thought, at the time, that standards and guidance documents such as BS 8500, BRE’s Special Digest SD-1 and ‘Sewers for Adoption’ should offer sufficient guidance on this. However, as concrete drainage products with lower exposure classes exist in the UK market, we felt it is important to explain how the exposure classes and chemical ground conditions affect the intended working life of concrete products. This new information can be found in the Guide’s ‘Forward’.


Pipelines’ hydraulic design

More information was added to this section as European Standard EN 16933-2 now supersedes EN 752 on hydraulic design of drains and sewers. Terms associated with SuDS and oversizing for surface water drainage were also added.


Pipelines structural design

All pipeline design load tables have been amended to account for loadings aligned to the Eurocodes. The cover depths included in these tables have also been expanded to include covers as low as 0.6m, and as deep as 10m. The ‘light road’ loading category has also been removed.


Box Culverts design

A new section was included on the structural design of box culverts in accordance to Eurocodes, which superseded the now withdrawn BS 5400 on bridge design a few years ago. There is also a more detailed section on the hydraulic design of box culverts with examples and guidance adapted from CIRIA’s Culvert Design and Operation Guide.


Installation of precast drainage products

More information on innovative pipeline lifting and installation solutions (such as the pipe lifter) was added. A section on the installation of box culverts was added too.


Future revisions?

It is understood that BS 9295 is undergoing a major revision which will affect options associated with the structural design of concrete pipeline systems. We do not think it will invalidate the content of this new version, but additional options associated with design (e.g. limit state design), trench width and bedding factors will need to be introduced.

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Precast concrete box culverts have traditionally been used as channels to divert watercourses where new construction creates a barrier to the natural pathway of flow. They are strong, durable and are available in a wide range of sizes. This makes box culverts extremely versatile and has resulted in them being used for other applications including: surface water storage, attenuation tanks, pedestrian subways, access shafts, service tunnels, sea outfalls and crossings beneath roads.


Unlike structures manufactured from other materials such as steel, precast concrete box culverts do not require additional protective treatments to prolong service life or improve performance in normal conditions of use. They do not rust and the smooth internal finish of the concrete ensures efficient flow characteristics.


The most common loads applied to the design of a box culvert are:

  • The unit’s self-weight
  • Where a culvert is buried, the weight of fill above the culvert
  • Where the culvert is installed under a road, the weight of road surface material (in addition to that of the fill)
  • Vertical live loads, such as those from vehicular wheel loads or pedestrian traffic
  • Horizontal live loads from vehicles braking or accelerating
  • Where buried, horizontal earth pressure loading applied to the culvert’s side walls
  • There will be a ground bearing pressure on the bottom of the box culvert
  • There might also be water pressure from inside, where the culvert is carrying a river for example, or from hydrostatic pressure from outside where the culvert is in a high water table of flooded ground

Members of the British Precast Drainage Association (BPDA) design and manufacture box culverts specifically to meet particular applications and defined loading conditions. Box culverts which are to carry highway or railway loading are designed to the standards and specifications as stipulated by the client. Box culverts can be specially made to higher loading requirements. Some box culverts can take LM1/LM2 bridge loadings at 0.25m of cover.


BPDA has an extensive library of useful information and guidance publications for designers, installers and asset owners. They are available to download free of charge from the BPDA’s website. The site also holds a comprehensive and searchable FAQ section and an online enquiry facility; go to

Posted by & filed under Pipes & Manholes.

In the UK, high pressure water jetting is widely used to clean and mostly to clear blocked sewer pipelines – often as an emergency operation. The European Standard BS EN14654-1:2014 Management and control of operational activities in drain and sewer systems outside buildings, Part1: Cleaning, states that “Maximum safe working pressures to avoid damage will vary according to the material of the pipe, condition of the pipe and type of nozzle”. Risk of damage to the pipeline can be reduced if the jetting nozzle is kept moving and the direction of the jet does not focus on the wall of the pipe. Damage in this way may be avoidable, but the risk of damage increases where there is an obstruction within the pipeline and the jetting nozzle cannot pass through the blockage


In 2005 the WRc published the Second Edition of the Sewer Jetting Code of Practice. This document provides guidance on good working practice when using high pressure water jetting equipment. The code establishes a maximum jetting pressure for pipeline materials, varying from 1500psi for brick sewers up to 5000psi for concrete pipelines – see Table 1 below.


Table 1: Water jetting pressure maximum limits for different pipe materials from the Water Jetting Code of Practice.


Material Concrete Clay Plastic Brick
Max pressure


5000 5000 2600 1500



It is generally accepted that smaller diameter pipes are most effectively cleaned with pressure as the source of energy within the pipes. In theory, if the code is closely followed, it should prevent damage to the fabric of drains and sewers from occurring, but the huge difference in maximum jetting pressures from 5000psi for concrete down to 1500psi for brick, can potentially lead to confusion. It would make sense if a maximum jetting pressure was applied consistently nationwide at a value known to result in effective cleaning and clearing of blockages. Sadly, the required pressure to shift some stubborn blockages exceeds the resilience of some materials and damage to the sewer is more likely unless the operation is carried out to the textbook and with extreme care.


For larger diameter pipelines there is an argument that flushing the blockage through using a large volume of water at lower pressure is an alternative to high pressure jetting. However, to generate a high flow rate, access to a drinking water hydrant or a large capacity water tanker will be required. This can be a more expensive, time consuming, wasteful and less environmentally friendly solution than using lower volumes of water jetted at higher pressure.  It is important that users understand the differences in the resilience of different pipeline materials to high pressure water jetting and the implications of using different cleaning and blockage clearing methods.


BPDA has an extensive library of useful information and guidance publications for designers, installers and asset owners. They are available to download free of charge from the BPDA’s website. The site also holds a comprehensive and searchable FAQ section and an online enquiry facility; go to

Sustainable Drainage

Posted by & filed under Pipes & Manholes.

It has been estimated by DEFRA that significantly less than 1% of public sewers are being renovated or replaced each year. If that rate of replacement is continued, it will take approximately 800 years before a new pipeline laid today can be expected to be replaced. No product carries a certificate to say that it will last 800 years. Most will claim a Design Life of between 50 and 125 years. This does not mean that a pipe product will cease to work efficiently at the end of this time because its service life may be very different.

Design life is usually the period over which an asset’s depreciation is calculated. Design life should not be confused with service life, which is the length of time a component can be expected to perform before its performance falls below the original design requirements without requiring renovation or replacement. A major advantage of precast concrete drainage systems is that they have a proven long service life, typically in excess of 120 years. This 120 year “reference service life” is a requirement for infrastructure design and asset management assessment standards such as PAS 2080 Carbon Management in Infrastructure and Series 1700 of the Specification for Highway Works in England (NG 1704).

In the UK some soils are more aggressive to pipes than others. As a safeguard precast concrete is manufactured using Design Chemical Class 4 concrete to achieve a working life of 100 years in soils with an Aggressive Chemical Environment for Concrete class AC-4, without the need for additional protective measures.

However, where a sewer, drain or other component within the system is liable to carry: a rising main discharge; septic sewage; untreated or corrosive trade effluents; and in situations without adequate ventilation, then additional protective measures should be considered to achieve a design life of, say, 120 years.

BPDA has an extensive library of useful information and guidance publications for designers, installers and asset owners. They are available to download free of charge from the BPDA’s website. The site also holds a comprehensive and searchable FAQ section and an online enquiry facility; go to

concrete drainage

Posted by & filed under Pipes & Manholes.

Minimum cover depths for concrete pipes vary depending on the vehicular traffic loading likely to be sustained by the pipeline. There are various industry specifications and Standards that state values for minimum cover depths based on these loading conditions.

Most loading conditions used for design either relate to patterns of wheel loading generated from main road traffic or to pipelines installed within fields where only occasional trafficking, for example from agricultural equipment may be expected. A third loading scenario is also sometimes used which is based on light road trafficking, for example traffic within a residential area, although heavier vehicles may have access to these locations and the main road loading condition is often preferred for design.

Cover depths of less than the minimum values published in these documents should only be used with the appropriate authority’s permission.

Sewers for Adoption, for example, requires the minimum depth of cover to the crown of gravity pipes without protection to be as follows:

  • In domestic gardens and pathways where there is no possibility of vehicular access, 0.35 m;
  • 0.5 m for domestic driveways, parking areas and yards with height restrictions to prevent entry by vehicles with a gross vehicle weight in excess of 7.5 tonnes;
  • Domestic driveways, parking areas and narrow streets without footways (e.g., mews developments) with limited access for vehicles with a gross vehicle weight in excess of 7.5 tonnes, 0.9 m;
  • Agricultural land and public open space, 0.9 m;
  • Other highways and parking areas with unrestricted access to vehicles with a gross vehicle weight in excess of 7.5 tonnes, 1.2 m.

It is common practice that pipes laid under main roads to have at least 1.2m of cover to avoid conflict with other services. This is also true for the grass verges at the side of the road and for light roads, which may on occasion need to carry main road traffic.

However, minimum cover depths could be reduced (with the appropriate authority’s permission) if appropriately bedded concrete pipes are used according to transport research organisation TRL simplified tables of external loads on buried pipelines. It says the inherent strength of standard Strength Class 120 concrete pipes enables the cover depth to be reduced to a minimum depth of 0.6m beneath a highway when installed in conjunction with a full granular bedding surround, Bedding Class S.

For concrete pipes laid in fields the BPDA recommends a minimum cover of 0.6m should be provided to prevent damage from agricultural operations.

  • Where concrete pipes are required to be laid in fields at cover depths of less than 0.6m BS9295 Annex A, A16 gives recommendations for protection.
  • The preferred solution is to use a reinforced concrete slab installed over the pipeline which extends to provide at least 300mm bearing each side of the trench. A layer of compressible material placed directly over the pipeline aids in the prevention of the slab loading directly onto the pipeline should settlement occur. Another method of protection at shallow cover depth is to use a concrete surround to the pipeline, Bedding Class A.

For pipelines under construction, where plant has to cross a pipeline, consideration should be given to providing dedicated crossing points which may consist of heavy steel plates bridging the trench to transfer vehicle loads away from the pipeline or additional cover material placed over the pipeline.

BPDA has an extensive library of useful information and guidance publications for designers, installers and asset owners. They are available to download free of charge from the BPDA’s website. The site also holds a comprehensive and searchable FAQ section and an online enquiry facility; go to