Posted by & filed under Design.

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 www.precastdrainage.co.uk

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

(PSI)

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 www.precastdrainage.co.uk

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 www.precastdrainage.co.uk

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 www.precastdrainage.co.uk

Joseph Bazalgette

Posted by & filed under SuDS.

Joseph Bazalgette

Sir Joseph Bazalgette (1819 – 1891) was the chief engineer of London’s Metropolitan Board of Works. Born in London on the 28th March 1819, Bazalgette began his career as a railway engineer. During this role he gained considerable experience in land drainage and reclamation.

When the London Metropolitan Board of Works was established in 1856, Joseph Bazalgette was elected the first and only chief engineer. The board of works was the first organisation provided to supervise public works all over the city.

 

Mid-19th Century London

In the mid-19th century, London was struck by a cholera epidemic, which killed over 10,000 people. At the time it was thought that the disease was caused by foul air that filled the streets of London. Along with the frequent occurrence of cholera outbreaks, a hot summer brought with it the ‘Great Stink’, which overwhelmed the city.

 

The Solution

The condition of Mid-19th Century London was an incentive for parliament to give legislation to the Board of Works. The Legislation allowed them to begin improvements on the sewers and streets. It was expected that the new sewer system would eliminate the great stink, which would reduce the outbreaks of cholera.

Bazalgette’s solution was to create a sewer network for central London that extended 82 miles. The underground network consisted of main sewers to intercept sewage outflows as well as street sewers. These new sewers would replace the raw sewage flowing through the thoroughfares and streets of London.

Although the impression was that foul air caused cholera was wrong, it didn’t mean that the sewer system was set up to fail. Instead, the sewers eliminated the disease by removing the contamination carried in the water supply.

The system was opened by the Prince of Wales in 1865 and was fully completed 10 years later.

 

Sustainable drainage systems today

Concrete drainage systems have been the material of choice for over a century. They can offer the most environmentally friendly and competitive installed option today.  Sir Joseph Bazalgette’s sewers were the first sustainable drainage system to be built. Overall the system required 670,000m³ of concrete and it is still in use now. The inherent strength and durability of precast concrete drainage can help protect the system during construction and throughout its long lifetime of operation.

 

To find out more about sustainable drainage systems, visit the British Precast Drainage Association (BPDA) website: precastdrainage.co.uk.

concrete manhole

Posted by & filed under Pipes & Manholes.

When inspection or maintenance of buried wastewater drainage systems is required a manhole is specified. They are most often built at the point where one pipeline connects to another, where a pipeline changes size, direction or gradient and at a spacing that enables equipment to be used effectively. Here we detail some advice for specifying manhole systems.

  1. Consider a precast concrete solution

It can take up to 40 hours to construct a manhole using traditional techniques. Construction in-situ like this can also involve working in wet and difficult confined spaces. This is where off-site manufactured precast concrete manhole base systems offer some big advantages. They are safer, quicker and cheaper to install. In addition, they are watertight, of consistently high quality, create less waste on site and have a lower carbon footprint.

  1. Each manhole should be correctly constructed for each specific location

Due to the precast concrete base being factory manufactured to a specific configuration, when the components arrive on site they can quickly, simply and safely be placed in position. This negates the need for lengthy site-based operations.

The BPDA estimate that a contractor using a precast manhole base system could save up to 50 per cent on installation time. Construction costs can also be reduced by 15 to 30 per cent, particularly when manholes are installed without a concrete or granular surround.

  1. Manholes should be compliant with appropriate Standards

The technical requirements for reinforced and unreinforced manholes are described in the European Standard BS EN1917:2002 Concrete manholes and inspection chambers, unreinforced, steel fibre and reinforced and the British Standard BS5911 Part3: 2010+A1:2014 Specification for unreinforced and reinforced soakaways.

This British Standard is referenced in Approved Document H of the Building Regulations, which deals with drainage and waste disposal. This document details the rules which construction of drainage and waste disposal systems must comply.

The BS is also referenced in Sewers for Adoption and the partner water utility publications throughout the UK. These require developers and installers to build drainage systems to a minimum standard and quality for adoption by the relevant water company.

The advantage of using a BS-compliant and Kitemarked precast concrete solution supplied by a member of the BPDA is that users can be sure that the product will comply with all necessary technical requirements.

  1. Will you choose a round or square manhole chamber?

One of the biggest advantages of using a concrete manhole is that concrete is very strong in compression. A circular precast concrete manhole exploits this trait. Its circular shape ensures that ground and hydrostatic pressure is evenly distributed around the circular shaft. This enables circular precast manholes to be installed to a far greater depth than precast manholes of ‘equivalent strength’ with flat sides and corners.

  1. Consider the need for access

Whatever the shape of the manhole, if it includes a ladder or step irons for access then users need to be aware that the Health and Safety Executive’s confined spaces regulations. These recommend a 900mm clearance between the ladder/steps and the back of the shaft.

Ladders and steps usually protrude by at least 100mm, so for compliance users will need to consider a circular manhole with a diameter no less than 1,050mm.

Precast manhole systems offer great versatility and are designed to accommodate all standard pipe materials and sizes. Existing precast manholes can even be retrofitted with new connections from future development without the need to replace the entire manhole.

  1. Minimise the need for granular backfill

The robust design and wide chamber walls of the factory manufactured precast concrete manhole base system means that the use of granular or concrete backfill can be eliminated, unless it is specifically required by the client. The excavation can be backfilled sooner using the soil that was excavated, thus making the installation safer and faster whilst simultaneously reducing the cost of backfill and disposal of the excavated material.

  1. Save on carbon emissions

Factory manufactured precast concrete manhole base systems also offer a significant saving in embodied carbon for the installation. The BPDA estimates that carbon savings could be as much as 43 per cent per manhole compared with traditional in-situ construction. A notable part of this carbon saving is the avoidance of concrete or granular backfill and the use of excavated soil.

The BPDA estimates that 15,000 tonnes of CO2 equivalent of embodied carbon would be saved annually if all manholes manufactured by the Association’s members changed from in-situ construction to the circular precast base system.

  1. Consider durability

The precast manhole base system is manufactured under factory conditions by quality assured processes. This ensures the finish and quality is to a higher and to a more consistent standard than could have been achieved on site. The combination of durable precast concrete and quality controlled offsite manufacturing process will ensure that a precast manhole system has a long service life.

For more information about concrete manholes visit the British Precast Drainage Association website.

FAQ

Posted by & filed under eNewsletters & eBlasts.

When designing, installing and maintaining drainage systems we know that difficult questions can arise. What is the installed cost? What is the carbon footprint? What is the minimum cover depth? What is the service life? Just a few questions which we have been asked over the years.

When using precast drainage products, it is important that you get the right information for the job. We recognize that you may have some important questions. There is now a place on our website where you can find answers to the most frequently asked questions about precast drainage. If you can’t find the question you need answering, you can simply contact us through our brand new enquiry system and we will ensure that your enquiry will be dealt with by an industry expert.

BPDA aims to give users all the information they need to complete their project successfully. For more information on the new FAQ, Search and Enquiry system click here.

20 reasons

Posted by & filed under eNewsletters & eBlasts.

Since the formation of the British Precast Drainage Association from the merging of the Concrete Pipeline Systems Association and the Box Culvert Association, the case for precast concrete drainage systems is stronger than ever. The new updated version of 20 Reasons to Use Concrete brings together in one useful booklet key benefits and references for precast concrete pipes, manholes, box culverts, sustainable drainage systems (SuDS) and other related drainage components.

Concrete drainage systems are at the heart of our sewerage network. It has been this way since the early 1860s when the Victorians introduced sewers into our communities for the first time. Their longevity, proven for over 150 years is just one of a number advantages offered by concrete which include reduced installation and whole life cost, lower environmental impact, inertia and high strength.

Concrete drainage products address the needs of the designer, installer and asset owner and have evolved to meet new challenges. This new booklet from the BPDA gives 20 reasons why concrete is the right choice today and for the future.

To download the booklet please click here. Or to request a hard copy please complete the Literature Request Form.

manhole

Posted by & filed under Pipes & Manholes.

In any construction project, bad ground conditions can create a wide range of problems and can even bring construction to a halt. This is why when Peter Harding Construction began work at St Wilfreds Academy in Blackburn, they knew they needed a drainage solution. The solution had to combat the poor ground conditions, not hinder the efficiency of their work, and ensure the health and safety of their team of workers.

After evaluating the site it was decided that orifice chambers and Hydro-Brake chambers were needed. However, this created problems relating to budgets and offsite design. BPDA member Marshalls CPM offered a solution by providing a full package of sealed 1200mm and 15000mm perfect manholes. They also provided off-site solutions for orifice and Hydro-Brake chambers. This allowed for many problems relating to chamber overflow to be overcome.

The Perfect Manhole system was used where possible. However, eventually, it was decided that due to the unusual ‘S’ style shape of the channel, a 1500mm sealed Catchpit that utilizes an offset inlet and outlet would be well suited for the project as well.

In addition, the client was presented a variety of pipeline design options. While plastic pipework was considered, this required using Class S Bedding. It was settled that precast concrete pipes would be the most ideal solution. This allowed for a lower overall cost and a reduced environmental impact as precast concrete pipes were installed with Class N bedding, which meant use of imported aggregate could be reduced.

The final result was an effect drainage solution that improved the poor ground conditions and accelerated the installation of the drainage requirements.

To read more please visit the BPDA website.

box culverts

Posted by & filed under Construction.

When a housing development in Lincoln was set to create 374 homes, a question was presented as to what drainage solution to use. BPDA member Forterra came to the rescue by supplying around 600 precast box culverts to the development.

Forterra, who worked together with the main contractor, Daniel Charles Construction, designed the drainage system to take surface water run-off from the development. The water is run through channels to control chambers. It is then stored into three large storage tanks, and discharged to a drainage ditch alongside the A46. Almost 2 million litres of surface water can be held in the drainage system, making it the ideal solution.

Measuring 2 metres long by 1.2 metres wide, and weighing around eight tonnes, it was expected that the delivery and installation of the box culverts would be tricky. Partner this with the difficult to access site, and you might expect to run into some problems. However, Forterra’s expertise meant that delivery and installation went very smoothly, forming runs of around 90 metres in length.

The box culverts were installed in 2 stages to ensure efficient and correct installation. The project for Forterra lasted 18 months, resulting in a well performing complete drainage system that the Construction Manager, Tony Higgins, and end client, Taylor Lindsey Homes, were very happy with.

To read more please visit the BPDA website.