Natalie Moore explores the methodology and process of using BIM to model the environmental aspects of the M4 Junctions 3 to 12 Smart Motorway Project.
In my earlier article, ‘BIM – starting with the basics’ (December 2015), I investigated the suitability of using Building Information Modelling (BIM) on a project of the scale and complexity of the M4 Junctions 3 to 12 Smart Motorway Project (SMP). Three years on, the implementation of BIM has significantly progressed.
The M4 Junctions 3-12 SMP is Highways England’s largest Smart Motorway scheme. Granted a Development Consent Order (DCO) in September 2016, the project is currently undergoing detailed design, and the first phase of construction started on-site in July 2018.
The environmental BIM inputs comprise: ecological constraints; information on badgers, great crested newts, dormice, bats, otters, water voles, reptiles and invasive species; and detailed landscape design.
The 2D ecological data layers, containing species and habitat locations, were created in a geographic information system and initially exported into AutoCAD, where they were converted into 3D elements using the civil engineering software Civil 3D. This makes the location of a badger sett or the extent of a pond easier to identify in the busy BIM landscape. These 3D layers can then be exported directly into the 3D design review package Navisworks, essentially creating a glorified 3D PDF of the original drawing.
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Figure 1: The dark blue cylinder is a badger sett, with the blue zone in the background representing water vole and otter areas. Attribute data behind the cylinder shows the information source.
Navisworks allows these 3D shapes to be compared against other physical items that fall within a certain distance or buffer in the model, in order to detect potential clashes. Clearance clash detection in Navisworks can be set to find any object within a certain distance of a certain 3D shape, such as a badger sett. Navisworks will then return a set of results of all items within that distance of the shape. Clearance could be set for any distance and any specific shape.
These results are then discussed with the design team. Is there a construction impact to that badger sett that wasn’t previously known? Will a badger licence be required? Are there design changes that can help avoid this? These discussions are led by the lead design ecologist and any potential mitigation is discussed during BIM clash detection meetings. It is important to note that in Navisworks you cannot alter shapes or the information behind the data, as it is purely a viewing tool – you would need to edit the information in the original program.
A similar process was followed for the landscaping design, creating 3D elements with differing heights for vegetation such grassland and trees. When combined with all disciplines, this is called a federated model.
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Figure 2: Red cylinders represent badger setts. The different shaded green areas represent different landscaping and planting areas – lightest green (almost white) is L1.1 verge and amenity grass. Mid-green is L1.5 open grassland. Darker green is L2.9 woodland.
My previous article mentioned that the ‘I’ in BIM relates to the information contained within the model. The attribute data behind each design element needs to be extensive, to allow more complex clash detection. For example, there must be sufficient attribute data to allow identification of steep slopes in the Geotech design, to confirm the suitability of proposed planting. Further clash detection could ensure the design does not extend beyond the DCO boundary, and that tall vegetation is not overhanging gantries and emergency areas.
Jon Dempsey, project information manager at Arcadis Jacobs, has been leading the BIM process to deliver the detailed design. “This is a first for a joint venture using BIM for Highways England,” he says. “Through implementing BIM, we are aware of the design issues much further in advance than we would have been previously, so we can rectify issues before construction starts. This should reduce the number of technical queries and requests for information on site, giving the design team a chance to resolve them before spades break ground. The data behind BIM was also used to produce a fly-through of Package 1 at recent Public Exhibitions. This innovative use of technology by Highways England was a huge success, positively received by the public.”
“A lesson learned from the M4 to take to further projects would be an understanding between the designer and the contractor on how we are intending to use the model on site during construction,” says Greg Dixie, BIM lead for Balfour Beatty Vinci (BBV). “There doesn’t appear to be an industry consensus on using the federated model for setting out purposes, including measurements, co-ordinates and sections. This generalised issue needs to be addressed within the industry to find a solution that takes us away from drawings. Addressing issues being caused, such as measurements not being trusted, will be the next step forward for construction.”
The M4 Junctions 3 to 12 Smart Motorway Project is just one example of a project at detailed design using BIM clash detection. The same process can be implemented on rail, property and many other projects. With the digital agenda a key focus within Arcadis and other consultancies, BIM is step in the right direction towards a point where contractors will no longer use 2D drawings but will require a fully integrated federated model.
Natalie Moore is senior environmental consultant at Arcadis Consulting
