Atkins' BIM strategy for Liverpool's £130m wastewater treatment works

Building information modelling (BIM) played a vital role in the construction of Liverpool's wastewater treatment plant on the banks of the Mersey. Discover how contractor Atkins used BIM to improve safety and reduce costs on the development.

BIM model of the treatment plant
BIM model of the treatment plant

Client: United Utilities

Contractors: Galliford Try Costain Atkins (GCA) Joint Venture at Liverpool

The strategy

The GCA project directors required Atkins to use a BIM strategy for the detailed design and construction of the £130 million project in April 2012.

With the implementation phase soon to start, project detail designers needed a strategy that included enough aspects of BIM to help the joint venture achieve BIM Level 2 competency.

The strategy was to adopt 3D modelling to drive the project forward in a collaborative and integrated method. In essence, the GCA approach was to get the right information to the right people at the right time and in the right format. This aimed to foster a working environment, so various BIM applications could be demonstrated at given opportunities in the design and construction process.

Scope of the works

The £130 million facility is a 16-cell dual-level sequence batch reactor (SBR), complete with feed pumping station, distribution chambers, blower building and motor control centre. The SBR has a footprint of 160m x 115m. Construction is taking place inside the old Wellington Dock. The site had to be dredged, filled with sand and emptied of water dredging before construction could start. The 836 reinforced concrete piles, of 900mm diameter, were then sunk to a depth of 20m to support the new structures.

Winning the hearts and minds of both the design and construction engineers was going to be key to successful deployment of the BIM strategy. Atkins' first action was to employ the services of Matt Lees, a 3D modeller of proven capability and experience to lead the computer-aided design (CAD) team. Matt would also act as information coordinator to establish 3D modelling as the accepted platform for the detailed design.

Design engineers more accustomed to traditional methods, were somewhat sceptical of using 3D and BIM to completely design the new plant. However, the CAD team were soon able to show that traditional 2 dimensional construction drawings could be rapidly developed from the 3D model. They also showed that the new methods would not cause delays in design or construction, and could help speed up much of the design process.

Within just a week of starting work on the design, the team had produced a 3D model of the piling layout and base slab for the SBR. The team also created completely dimensioned and annotated 2D plans and sections for RC detailing. Co-ordinates for the piling layout were automatically generated by data extraction from CAD and then exported to an Excel spread sheet for the surveying team to download for setting out on site.

From the outset, the 3D model was created as a design and construction model. Adding the components as separate entities and individual concrete pours as objects, allowed for rapid changes to be made. This established the model as the hub of the design process and as a major collaboration tool. Engineers and designers realised the benefits of reviewing a virtual model which highlighted design change opportunities. Value engineering (VE) exercises were communicated to the client to show improved design. This led to quicker delivery, reduced materials and improved safety and operational benefits.

Value Engineering – Feed Pumping Station

On receipt of the definition phase design of the Feed Pumping Station, detail designers were quick to identified a VE opportunity. Raising part of the basement level could reduce the size of the coffer dam and produce a significant decrease in the amount of concrete required. The design team had a three week window to put forwards these design improvements to the client. The client's definition phase 3D model proved instrumental in this task.

The raising of the slab also meant that the internal floors were now all at one level. This provided improved access to equipment for both installation and operational purposes, contributing to improved all round safety. This was also highlighted through the proposed addition of an extra bay at ground level to the FPS building. The bay provided covered access for a flat-bed vehicle to reverse into the facility, allowing for dry floors and shelter to operatives during operations.

Further ideas were incorporated into the proposal following design reviews, and with the model updated to reflect these. Modifying the slab allowed for the reduction in the area covered by a crane (for access and egress of process plant equipment). This resulted in the reduction of structural steelwork and removal of walkways and handrails.

The model was also used to create an animation sequence to prove that the reduced reach of the crane would still be sufficient for removal of specific items of plant. It showed the swept path that items would pass through for lifting, traversing the facility, and delivering to the loading bay. This also helped to determine the best location for handrails around openings, and in ensuring clearance for objects and in protecting workers' safety during lifting activities.

The information co-ordinator estimates that this process, if done using 2D drawings, would have taken up to five times longer. Time limits would have made it impossible to gather together the information necessary. This would have included various 2D drawings, retrieving information, distributing it for comment and getting approval.

He said: "We used the model to show to our client how the proposed re-engineered solution would work. We demonstrated first to our construction team, then to Unitied Utilities' engineers and operations staff. We illustrated that the suggested changes would decrease the amount of material required, and therefore reduce costs. The proposed modifications were contributing to improved operational safety by addressing several Access Lifting and Maintenance issues."

Weekly design meetings help pick up design changes. The meetings take place on site and include all stakeholders, the customer, plus the process plant vendor. The model used significant detail and granularity from the outset. This allowed for the removal of individual items, including walkways. It was possible to show that removal did not harm operation and maintenance, or impact on safety.

The adopted strategy helped to develop the design process as a BIM workflow. This workflow included an intelligent 3D model, containing a rich set of inter-related information. The model allowed for the evaluation of many more design opportunities. Traditional drafting centric workflows would not have allowed such early identification of these opportunities. Early identification provides greater ability to impact cost and performance and reduce the costs of the design changes.

Construction sequencing, cost and carbon

By creating the model with such granularity, it was possible to align it to the construction programme (4D timelining). This illustrated the sequence of works and helped refine constructability.

Working hand in hand with the construction manager, and using his activity schedule for the construction phase of the sub structure, the model was created in line with individual sequenced events. From piling, cofferdam construction, excavation, support and temporary works, through individual concrete pours to structural steelwork erection. The model was then imported to Navisworks and a timeline created in accordance to the project plan, showing day, date and total time elapsed.

The planner could then evaluate his options, make refinements, with the model used to inform the programmers. Reports in the form of an xl spread sheet were extracted from the 4D model and then fed into Primavera to update the project plan.

Model of wet well benching flow splitters

With the model created at component level and linked to the timeline, it is showing any programme slippage.

Red indicates delayed activities that will clash with on program activities (indicated in green). This helps highlight when program re-sequencing and optimisation are necessary.

To show project spend, rates taken from the Bill of Quantities were added to the timeline and embedded into the model. This illustrated not only the cost of materials but also the cost of installation or placement. For example, demonstration of the price for provision and placement of a planned amount of reinforced concrete in any particular pour, and a cumulative total at any given point in the construction.

Keen to promote and show sustainability and carbon awareness, Atkins also added Carbon Embedment to the timeline. Atkins did this by aligning the equivalent carbon tonnage per tonne of concrete poured to ease Carbon analysis as the project progresses.

Collaboration and supply chain

Giving all staff access to the co-ordinated model and associated information helps ensure the greatest benefits from BIM. Publishing of updates to the model takes place daily. The whole project team can use free model viewers to visualise changes and retrieve information.

The model is also made available in the project induction room. Health and Safety can use the model to help provide Safe Systems of working, tool box talks, site inductions, and reviews by client operations staff.

The model is the primary communication tool at the weekly Design Review meeting. The model capture information such as actions from meetings and details about responsibilities for tasks. Actions are then stored on a data management system for future access. This helps to ensure that all identified tasks are actioned

Actions from meetings are then distributed with screenshots and mark-ups according to tasks. Sketches and screenshots comply to the project naming convention. Numbered accordingly, these outputs are set out on a standard drawing sheet. This means that if sketches are accepted and refined into workable solutions, only the document name needs altering to make it an 'official' drawing.

The Information Co-ordinator issues daily updates to the distributed model. Engineers review the model and associated changes using the free viewer and mark-up tools. They can send comments and annotations to engineers or designers who make the necessary changes. These result in visual changes within the model, using colour changes to components enabling easy identification by the rest of the team. The Co-ordinator picks up the changes and follows the correct process to incorporate them into the model for re-distribution the following day.

Delivering expectations, allaying concerns

A three-day workshop helped capture BIM expectations, led by Paul Heath, Atkins' CAD and BIM Manager, and Matt Blackwell, Costain's Group BIM Manager. Paul and Matt spent time with each project lead to learn their requirements through a collaborative and inclusive approach.

Heath states that "Interviewing the heads of each discipline helped us to identify requirements and define expectations as to what BIM should deliver and the value it could add to the project. The value of this working example of BIM model for project methodology, with 3D modelling leading the design, is easily demonstrated by the fact that construction drawing deliverables are on schedule, with just three civil CAD designers employed on the project. Live sectioning from the model has reduced 2D drawing time and effort, enabling greater efficiency in delivering both original drawings and design iterations.

Blackwell agrees: "When we started this project we knew that working in a collaborative environment using BIM processes and tools would help us to deliver a higher quality product more safely and at lower cost. Expectations for the project are being realised and initial concerns allayed. Using the model in value engineering exercises has produced construction cost savings on the major structures. The flexibility of the model due to its granular make up will also future proof it for any asset management (6D) requirements of the facility going forwards.

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