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Rather than rely on the traditional 2D workflows for detail design of this flagship project, the GCA JV Board of Directors recognised that the delivery of the project could be greatly enhanced by employing Building Information Modelling (BIM).

As civil and structural detail designers for the project, Atkins, one of the world's largest engineering consultancies, with more than 100 offices in the United Kingdom, was charged with leading the implementation of the BIM strategy.

According to Paul Heath, BIM lead adopter for Atkins Water Operations, BIM has proved to be a time- and cost-saving asset on the project: "A BIM process is built around 3D models, and helps the whole team to better understand the project before and during construction. Large, complex projects progress with fewer issues when you use BIM. There were numerous instances of problems avoided and value engineering opportunities recognised early in the design stages, which greatly contributed to cost savings."

THE NEW WAY OF WORKING
The team used BIM to improve coordination, buildability, operability, and maintainability on the wastewater treatment plant expansion project. BIM Specialist Matt Lees explained, “The model helps us design for improved constructability and more efficient operations and maintenance. Using the model as a reference, operations staff from the client helped us understand how to optimise the plant for maintainability and safety.”

THE CHALLENGE
The client, United Utilities, was responsible for the concept and definition phases of the project, with GCA JV taking over for the implementation phase and providing detailed design and construction services.

A number of complexities stood out on the project. The new plant is located in an existing operational dock, which is subject to a preservation order by English Heritage. This meant that the design had to avoid damage to the walls. The dock was also still operational, so the gates had to be closed and a permanent closure constructed prior to dewatering, sand infilling, and piling.

"A facility of this type and size would typically occupy a huge swath of land," says Heath. "You expect acres of space to work with, but on this project the footprint is very confined. The solution was to go up rather than out, so there are eight treatment cells over another eight treatment cells. We thought that designing in 3D could help us manage all that complexity, and that using Autodesk Navisworks Manage software could help us coordinate all the models required by the project."

THE SOLUTION
Starting with the main SBR (sequence batch reactor) structure, the design team created a 3D model of the piles, base and wall starters, cutting 2D plans and sections from the model using Autodesk AutoCAD and Autodesk AutoCAD Plant 3D software.

The 2D drawings were then sent to the Global Design Centre in India for reinforcement detailing. The speed demonstrated in this 'new' workflow helped to quickly allay any concerns that designing in 3D would slow down the production of the 2D construction drawing deliverables.

Matt Lees, for Atkins, explained further. "We designed in 3D from the outset, and then generated 2D drawings from the models," he says. "Those who were hesitant saw that you can easily create a 2D drawing from the 3D model if you need one. People realised they could get the advantages of 3D without a downside.

"Interestingly, we did have a few project participants who chose to use 2D workflows against our advice or requirements," adds Heath. "It's been a relatively issue-free project, but those 2D-based processes have been a large part of the few issues that we have encountered."

A COORDINATION HUB
On a project the scale of the Liverpool Wastewater Treatment Works, there are dozens of participants, with subcontractors and the equipment supply chain submitting detailed models and designs for their particular elements of the project. The detail design itself even involved an Autodesk AutoCAD Civil 3D model, which was used with barometric survey data to help calculate silt volumes contained in the dock prior to construction commencement.

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