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BIM for Water: Savings in the pipeline

In north east England the growing use of BIM on infrastructure projects is helping to turn one water and sewerage company’s efficiency ambitions into reality.

Northumbrian Water’s technical services framework consultants have been given a mission. Upon launching the 10 year framework in 2011, the company challenged its consultants to achieve a significant reduction in project costs over the course of asset management plan 5 (AMP5) which runs from 2010 to 2015.

Northumbrian Water was focused on the need to manage project spending more effectively and to deliver more for less as alluded to in the Egan Review of the construction industry and frequently demanded by industry regulator Ofwat. As the largest construction client in north east England, the water company could see plenty of opportunities to bring down the cost of carrying out necessary capital investment.

With this efficiency target in mind, framework consultant Mott MacDonald opted to demonstrate how far this cost efficiency challenge could be met through the use of Building Information Modelling (BIM) - and found the perfect opportunity to do so in a project to remodel an underground combined sewer overflow (CSO) at Acklam Road in Thornaby, Teesside.

This was an ideal pilot project to trial the use of BIM technologies and processes under the Northumbrian Water framework.

“The Acklam Road project was reasonably complex and big enough - at a capital cost of £1.5M - that we could find significant efficiencies. But it was not so big that trialling new processes would create unacceptable risk,” says Mott MacDonald project director Alan Hymers.

The project called for the decommissioning of an existing screening facility and construction of a new powered screening facility with a relocated discharge. Key objectives for the new design were to improve hydraulic performance - in order to avoid the historic problems of unsightly debris being strewn about the watercourse, and the need for frequent maintenance visits - and make maintenance access easier and safer.

Early stakeholder satisfaction

To meet Northumbrian Water’s cost-cutting expectations, Mott MacDonald’s use of BIM had to contribute to efforts to optimise efficiency. One of the biggest potential efficiency drains on any project is redesign, and there was plenty of opportunity for this obstacle to loom on Acklam Road. With many stakeholder demands placed on the new asset, there was a multitude of details to get right - or face requests for costly late-stage changes if stakeholder expectations were not met.

External stakeholders included planning authorities, which had placed stringent requirements on the appearance of the above-ground structure, and the Environment Agency, which had imposed a legal obligation for water quality to be improved at the discharge. Northumbrian Water was pursuing numerous objectives of its own - from ensuring hydraulic performance and maintenance access were appropriate, to ensuring that the new structure would redress the negative publicity which was generated by the old CSO’s poor performance.

The library means that we design each component once and in theory we can use that object many times

Alan Hymers, Mott MacDonald

BIM helped to ensure that stakeholders were involved and satisfied from an early stage, thus dramatically reducing the likelihood of expensive design changes and delays during construction. Mott MacDonald used BIM to share the project with the client’s health and safety, maintenance, operational and design acceptance teams in a virtual pre-construction environment, making communication of the project details more frequent and more effective.

As a result, Hymers says, “there were minimal changes to the design once the project got to site. If we had had to start moving things about at that stage, it would have added considerable cost.”

“In operational meetings, you have about three hours to communicate everything you have designed for the last three months, and all the rationale behind it,” says Mott MacDonald project manager Charlie Bell. “You need to get to the point where the client fully understands the work, so they can fully buy into the design and give feedback on it. BIM really helps to get to that point of understanding quickly and effectively.

3D BIM is also an avenue to get the client involved in the design process, further ensuring that it is aware of and happy with what will be built, says Bell. “2D drawings are static and less tangible, but we can show them a 3D model, walk round it with them and change things like local control panel locations and edge protection while they watch.”

Design once; use repeatedly

Mott MacDonald used Acklam Road as a pilot for another means of avoiding needless repetition of design work: developing a library of reusable design content. The catalogue includes commonly used elements such as pipes, manholes and screens which can be repeatedly dragged and dropped into 3D BIM models on any project. Variables such as dimensions can be customised on some items, such as pipes, and all library content aligns with the Civil Engineering Standard Method of Measurement (CESMM3) system, commonly used for preparing bills of quantities and cost estimates.

Although the library has already realised efficiencies on Acklam Road, the initial time requirement associated with setting up the library and its contents means that the catalogue will reach its true potential as a cost saver over the course of the whole AMP - and potentially beyond. “The library means that we design each component once and in theory we can use that object many times,” says Hymers. “We have now got that efficiency locked in for future projects.”

The Acklam Road model was also linked with costing software - known as 5D BIM - meaning that cost estimates and bills of quantities could be generated quickly and easily, regardless of whether model elements were drafted from scratch or extracted from the BIM library. Using 5D generates time efficiencies of around 50%, Hymers estimates, and improves accuracy. In fact, data from the Acklam Road model highlighted errors made by others.

Hybrid design in restricted space

The hybrid precast/insitu concrete roof of the main structure was a key contributor to cost savings on Acklam Road - and, again, BIM played a vital role. The hybrid roof and beam solution was chosen as the best match for the limited space available, and offered a 50% materials saving compared to a wholly precast roof, which would have had to have been twice as thick.

Necessary headroom and working space combined with level restrictions from planning made it impossible to use fully precast roof panels, but placing and withdrawing formwork for a wholly insitu roof was equally problematic. The resulting leaner design comprised precast shutters fitted around structural beams, with an insitu screed cast on top. BIM was hugely advantageous in evaluating the options and ensuring that construction of the cost-efficient hybrid solution was viable, given the restricted conditions.

“The 3D model helped us to see what space we had available to work in,” says Mott MacDonald BIM software modeller Chris Richards. “We knew exactly what the tolerances were and where to put the screen openings. Similarly, when the client asked for a stairwell we had to design it around the structure’s support beams. With 3D we could see exactly what headroom tolerances we had; with 2D I don’t think we would have been able to do that as accurately.”

The continuing efficiency journey

Through improved communication, visualisation, collaboration and accuracy, BIM has successfully proved its worth on Acklam Road, both in lowering costs and simply enabling better design processes. With Acklam Road deemed a successful pilot project, Mott MacDonald is now moving forward to implement and explore further uses of BIM for Northumbrian Water.

Potential future efficiencies in the computational fluid dynamics (CFD) modelling process were identified on the Acklam Road project. It demanded complex CFD work to ensure the new CSO could diffuse high velocity flows and deal with varying flow rates. The resulting CFD data - which recommended the inclusion of three large diffuser bollards to guide flow toward the CSO’s three screens - was then manually entered into the BIM model. The Mott MacDonald team will streamline this process for future projects by directly transferring data between BIM and CFD software, creating better links between the two models.

With 3D we could see exactly what headroom tolerances we had; with 2D I don’t think we would have been able to do that as accurately

Chris Richards, Mott MacDonald

Similarly, Richards and colleagues have developed a bespoke interface to enable direct data conversion between sewer modelling and 3D design software. This dramatically reduces duplication of work and eliminates a break in the design process. The software, christened Info3D, is now primarily being used on a sewer flooding programme for Northumbrian Water, comprising numerous sewer upgrade projects.

On sewage treatment projects including Barkers Haugh sewage treatment works in Durham, Mott MacDonald has ramped up the use of laser scanning technology, importing survey data directly into BIM as a ready-made 3D model.

On Barkers Haugh - which had to remain live and operational throughout upgrade works - Mott MacDonald has also used BIM to analyse the contractor’s 4D construction programme in a virtual environment, ahead of works commencing.

Northumbrian Water and Mott MacDonald are also looking ahead at the possibility of using BIM for asset management. “The more ways you can use a BIM model, the greater value it has to the client,” says Richards. “For example, you realise efficiencies for the client by using BIM to track maintenance tasks and identify maintenance trends.”

By continuing to implement and explore BIM as a means of lowering costs, improving project processes and enabling clever design solutions, Mott MacDonald is helping Northumbrian Water to achieve the upgrades it needs without excessive risk or cost. In light of the BIM successes of recent projects, the efficiency goals for AMP5 seem more achievable than ever.

Watch animations of the Acklam Road 3D model and a selection of other Mott MacDonald projects in the film “BIM Research to Reality” here.

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