How BAM planned the demolition of Gateshead flyover in 4D

While the flyover was a complex feat of engineering when it was built in the 1960s, its demolition presents an even greater challenge. At the time of its construction, there was no requirement to produce detailed demolition plans. As a result, the team returned to the original archive drawings, working from first principles to understand the load paths through the bridge, how it behaves, and how it would respond during progressive dismantling (see image below).

The scale of the structure, its proximity to surrounding buildings and live roads, and the reliance on extensive temporary works meant that traditional planning outputs alone could not fully communicate the sequence, risk and constraints involved.

From an early stage, the project team recognised the value that a 4D model could offer – not just as a visual output, but as a practical planning tool. The process began with an initial meeting to define how the model would be used and what the project team needed from it. This was crucial in setting expectations and establishing scope, as a 4D model is only as effective as the information that underpins it. At this point, existing data was reviewed, and gaps were identified, highlighting where additional information would need to be developed in-house to accurately represent the proposed methodology.

The information provided to support the model included the construction programme from P6, an existing 3D model of the flyover, a 3D topographical survey, a non-geolocated model of the propping system, and a series of 2D temporary works drawings showing elements such as scaffold, excavator runways and road protection mats.

While this formed a strong foundation, it quickly became clear that additional modelling work would be required to fully capture the complexity of the demolition sequence and the interfaces between permanent works, temporary works, plant and traffic management.

To address this, a significant amount of supporting information was produced in‑house. This included a refined 3D topographical model, which in turn helped the development of a context model produced in Infraworks to provide a wider urban and highway context, and detailed placement of the props along with associated stone pads.

Additional elements, such as parapets, indicative delamination survey zones, and missing parts of the existing model, such as abutments/reinforced earth, were also modelled to ensure the model was as close to the real world as possible.

Temporary works formed a major component of the model. Protective measures such as protection of one of the footbridges, a scaffold to protect adjacent buildings, protection of the pedestrian subway, and works to partly demolish the Hilda House car park were all modelled explicitly, rather than implied. As mentioned above, stone ‘runways’ and road protection mats also had to be modelled from the 2D temporary works drawing.

Plant was also represented in detail, including excavators with the correct attachments, such as buckets, munchers and debris protection screens. Traffic management was not treated as an afterthought either: road closures and diversion routes were incorporated, so the impact on the surrounding network could be visualised alongside the demolition works.

Once this modelling work was complete, everything was brought together in Synchro 4D Pro. The model was then carefully structured and linked to the programme, allowing activities to be visualised spatially and temporally. This is where the real value of 4D planning began to emerge. Working closely with the site team, the model was developed and refined over several weeks. Sequences were adjusted, assumptions were tested, and the programme was optimised according to what the model revealed.

The 4D model was used during collaborative planning sessions on site, where it helped to support discussions with subcontractors and the wider delivery team. Being able to see the sequence, access arrangements, and temporary works in context allowed issues to be identified far earlier than they otherwise would have been, reducing risk and improving confidence in the planned approach.

Another important step was ensuring the model could be used by the site team beyond pre‑recorded videos. To support this, in-house training was delivered for the Synchro OpenViewer to enable team members to navigate the model themselves. This allowed the 4D model to be used in daily planning conversations, rather than being limited to formal presentations or static exports.

The Gateshead flyover scheme clearly demonstrates the benefits of proper 4D planning when embedded into the project rather than treated as an add‑on. The model improved understanding of complex demolition sequences, helped to identify and manage risk, supported programme optimisation, and significantly enhanced communication across the project team.

Most importantly, it created a shared visual language that allowed engineers, planners, agents and subcontractors to engage with the plan in a meaningful way.

By the time demolition began, the value of the 4D model had already been realised through planning, coordination and risk reduction. By integrating programme, temporary works and site constraints into a single visual environment, the team was able to develop a more robust and well-tested demolition strategy ahead of works starting on site.

As the project progresses, the model will continue to play a key role in supporting delivery, with further benefits expected to emerge through its use in tracking progress, refining sequencing, and maintaining alignment between the planned approach and site operations.

Ben Thompson is production specialist (4D) in BAM's Digital Project Solutions team.