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Pushing The Limits Of BIM


Network Rail has taken 4D building information modelling (BIM) further and longer than it has ever been before.

While BIM should be a familiar term to most, 4D is less well used. The introduction of the fourth dimension, time, into BIM, enables the various parties (consultants, contractors, clients) involved in a project to cycle through the various designs to see the construction timeline come to life. Mistakes can then be made in the office, rather than the work site.

4D BIM has been used once or twice on rail projects before, including Crossrail, and on a blockade at Walthamstow in east London on the Victoria Line last year. But those were projects at most 200m long, involving 2,000 lines on a Gantt chart, which displays activities (tasks and events) against time.

The Gospel Oak to Barking Line electrification project is a worksite 14 times as long, and with three times as many Gantt lines for the project management team.

Over 10 months the north London Overground line will get new overhead electric lines, while four sections of track will be lowered, four bridges rebuilt and a further six modernised. There are sections of slab track and ballast track, on a tight two-line corridor, using tiny clearances around Victorian infrastructure – all while reducing disturbance in high-density neighbourhoods.

To manage the Gospel Oak to Barking line’s complexity, Network Rail went for 4D BIM early on, opting for a single and simple piece of bespoke and interactive programming.

The company offering the software is Freeform, led by James Bowles and Liam Clarke, former employees of Bam Construction and Synchro respectively.

“A bit crazy”

Freeform has mainly worked mainly in construction, on smaller and more vertical projects. So Bowles calls the 20.8km aspect of this one “a bit crazy”.

“The challenge and opportunity at this scale – it was quite a broad task.”

The task begins with logging and digitising all elements of a project – plant, actions, manpower. Then by adjusting one element in a plan, the software instantly reveals the future implications for other elements, and any conflicts that might arise.


So can you experiment with the software settings and brainstorm solutions? “It’s not a mega-computer that solves problems on the spot,” says Network Rail project interface manager Brett Chatwin says. “But it’s the certainly the closest thing towards being able to do that.”

This full digitisation of the project cost about £120,000. But Chatwin says it has paid for itself many times over.

“The reason we went for a model rather than a paper-based exercise was that every time there was a change to the programme, you have to go from scratch and do the whole thing again. The model is much more flexible and has all of the links built in, so, if you move one thing,  you’re really moving about 10 to 15 [later in the plan].

“There were four or five instances where, if we didn’t use that modelling, we would have gone out and made mistakes. And you’re looking at £75,000 to £80,000, every time you lose a weekend’s work. And because of the nature of the business you can’t just start late. So pretty quickly it’s four to five hours lost and that’s a whole weekend lost.”

An unexpected, but welcome, bonus has come from the virtual reality function. Train drivers returning to work on the line will be re-introduced to the trains using virtual reality headsets. The drivers use the 3D model to get to know how the new line works (where the new signals are, how tight the corners) which saves two weeks of test runs after the project is complete.

But it is the start of the project where Network Rail and Freeform agree that digitisation has most benefit. In an ideal world, 4D BIM should happen as early as possible, they say, even at the project’s inception.

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