Atkins BIM strategy for Liverpool wastewater treatment works

As part of the United Utilities (UU) Process Alliance, the Galliford Try Costain Atkins Joint Venture at Liverpool, Atkins have used BIM to help deliver significant cost and safety benefits on the development of a new wastewater treatment facility being constructed adjacent to the existing Sandon Dock site.

Directed by the GCA board of Directors to employ a Building Information Modelling strategy for the detailed design and construction of the £130 million project in April 2012, and with commencement of the implementation phase imminent, project detail designers had to quickly develop a strategy which could deliver sufficient aspects of BIM to enable the joint venture to 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 in order to foster a working environment in which, various BIM applications could be demonstrated at given opportunities in the design and construction process.

Scope of the works

The £130million facility is a 16 cell dual level Sequence Batch Reactor complete with Feed Pumping Station, Distribution Chambers, Blower Building and MCC, the SBR having a footprint of 160m x 115m.The new facility is built inside the old Wellington Dock which had to be dredged of silt, then simultaneously sand filled and dewatered prior to construction. 836 reinforced concrete piles at 900mm diameter were then sunk to a depth of 20m to support the new structures.

The £130million facility is a 16 cell dual level Sequence Batch Reactor complete with Feed Pumping Station, Distribution Chambers, Blower Building and MCC, the SBR having a footprint of 160m x 115m.

Winning the hearts and minds of both the design and construction engineers was clearly going to be key to successful deployment of the BIM strategy, and Atkins immediate action was to employ the services of Matt Lees, a 3D modeller of proven capability and experience to lead the CAD team and to act as Information Co-ordinator to establish the 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 fully design the new plant. However, the CAD team were quickly able to demonstrate that traditional 2 dimensional construction drawings could be easily developed from the 3D model and that the new methods would not cause delays in design or construction, and could actually 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, together with fully 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, with all components as separate entities and individual concrete pours defined as objects, which enabled changes to be made quickly. This established the model as the hub of the design process, and as a major collaboration tool, as engineers and designers quickly realised the benefits of reviewing a virtual model which highlighted design change opportunities. Value engineering exercises were easily communicated to the client to demonstrate improved design leading 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 quickly identified a VE opportunity whereby, raising part of the basement level could greatly reduce the size of the coffer dam and significantly decrease the amount of concrete required. The design team were given 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, highlighting how BIM is being used right from concept stage through to detailed design.

The client’s definition phase 3D model proved instrumental in this task, highlighting how BIM is being used right from concept stage through to detailed design.

The raising of the slab also meant that the internal floors were now all at one level, providing 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, providing covered access for a flat-bed vehicle to reverse into the facility, thus affording dry floors and shelter to operatives during operations.

As the design was reviewed and the model updated, further ideas were incorporated into the proposal. Modifying the slab meant that the area to be covered by a crane (for access and egress of process plant equipment) was also greatly reduced resulting in the reduction of structural steelwork and removal of walkways and handrails.

BIM generate model showing structural steelwork

The model was also used to create an animation sequence to demonstrate that the reduced reach of the crane would still be sufficient for removal of specific items of plant, showing 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, ensuring clearance for objects and ensuring operatives safety during lifting activities.

The information co-ordinator, estimates that this process, if done using 2D drawings, this task alone would typically have taken up to five times longer, requiring the gathering together of numerous 2D drawings, retrieving information, distributing for comment and receiving approval all of which could not have been completed in the time frame to meet the requirements of the programme. He describes, “We used the model to show to our client how the proposed re-engineered solution would work, demonstrating first to our construction team, then to UU engineers and operations staff. We illustrated that the suggested changes would decrease the amount of material required, and therefore reduce costs, and that the proposed modifications were contributing to improved operational safety by addressing several Access Lifting and Maintenance issues.”

Design changes are picked up within the weekly design review meetings, held on site and including all stakeholders, the customer plus the process plant vendor. The model was created with granularity from the outset, therefore, individual items, including the walkways, could be quickly isolated and removed, proving that the removal did not impede operation and maintenance and had no detrimental impact on safety.

The adopted strategy helped to develop the design process as a BIM workflow, in which an intelligent 3D model, containing a rich set of inter-related information, has facilitated the evaluation of many more design alternatives. These opportunities have been identified much earlier than in a traditional drafting centric workflow, providing greater ability to impact cost and performance and therefore decreased costs of the design changes.

Construction Sequencing, Cost & Carbon

The granularity of the model allowed it to be aligned to the construction programme (4D timelining) to illustrate the sequence of works and refine constructability. Working closely with the construction manager, and using his activity schedule for the construction phase of the sub structure, the model was created in accordance 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. This allowed options to be evaluated by the planner, refinements to be made and 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 being used to visually demonstrate any programme slippage. Delayed activities are indicated red to illustrate where they will clash with current on program activities (indicated green), This visually highlights where a program re-sequencing and optimisation is required.

To demonstrate project spend, rates taken from the Bill of Quantities were added to the timeline and embedded into the model to illustrate 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 demonstrate sustainability and carbon awareness, Atkins also added Carbon Embedment to the timeline by aligning the equivalent carbon tonnage per tonne of concrete poured to facilitate Carbon analysis as the project progresses.

Collaboration and Supply Chain

To ensure maximum benefits are realised from BIM, all staff in the site office have access to the co-ordinated model and its associated information. As the model develops, daily updates are published which can be accessed by all, using free model viewers to visualise changes and retrieve information. The model is also made available in the project induction room, and can be used by Health and Safety to facilitate Safe Systems of working, tool box talks, site inductions, and reviews by client operations staff.

The model is used as the primary communication tool at the weekly Design Review meeting (which includes all stakeholders, including architect, designers, engineers, client and supply chain), and is used to document actions from the meeting and capture information about who is responsible for what tasks. These actions are then stored on a data management system and can be referred to at any point, to ensure that all previously identified tasks have been actioned.

The actions from the meetings are then distributed with screenshots and mark-ups according to tasks. Sketches and screenshots comply to the project naming convention, numbered accordingly and are set out on a standard drawing title sheet, such that if sketches are accepted and refined into workable solutions only the document name needs altering to make it an ‘official’ drawing.

Daily updates to the distributed model are issued by the Information Co-ordinator. Engineers review the model and associated changes using the free viewer and mark-up tools, sending 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 information coordinator 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

BIM expectations were captured during a three-day workshop with Paul Heath, Atkins’ CAD and BIM Manager, and Matt Blackwell, Costain’s Group BIM Manager, spending time with each project lead to learn their requirements through a fully 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 projectmethodology, 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 greatly 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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