55 hours with no slack: simulation secures a smooth construction process
A bridge replacement inside a very tight possession, with demolition, launch and reinstatement of bridge and track in the same window. The rule here: a smooth construction process, nothing left to chance. Simulating the construction process let us safeguard logistics and mass movements and head off critical conflicts early. On site, the possession held.
The challenge
The replacement of the Else railway bridge had to be delivered within an exceptionally short possession of just 55 hours. Every critical construction phase had to fit into that window: from demolishing the existing structure through lifting in and launching the new bridge to reinstating the track. There was no room for delays or unplanned events.
- A possession of only 55 hours
- Demolition, launch and reinstatement within one continuous window
- Strong interdependence between construction process, logistics and equipment
- No scope for rework or time reserves
- Safeguarding a smooth construction process before work started
How we went about it
During detailed design we reproduced and analyzed the planned construction process digitally with our process simulation software. The actual output data of the intended machines, the site environment and the site setup drawings were brought together into one simulation model. By linking the construction process, logistics and spatial constraints, we could test whether the plan worked and identify potential conflicts early.
- Modeling the entire site environment
- Integrating the site setup and logistics areas
- Simulating the planned construction process with real machine and output data
- Visualizing material and mass movements
- Validating transport routes and logistics processes
- Analyzing spatial and temporal dependencies
The outcome
The simulation-based analysis meant critical conflicts could be identified, assessed and resolved together with the project team before construction began. The alternatives developed were simulated, validated and checked for their effect on the schedule and on logistics. The result was a robust, build-ready construction process – and on site, the 55-hour possession held.
- Early identification of spatial and temporal conflicts
- Proof of deliverability within the 55-hour possession
- Validated logistics and transport concepts
- Transparent presentation of the construction process and mass movements
- Risk reduction before work started
- Possession met on site
From identified conflicts to validated solutions
Spatial and temporal conflicts uncovered in the simulation were discussed in the regular project meetings, resolved and validated again, chronologically along the construction process. The conflicts built on one another: each solution triggered the next.
The planned excavator position clashed with existing infrastructure and could not reach the working area.
Repositioning the excavator and replanning the excavation.
Moving the excavator created longer haul routes for the spoil, which would have overrun the possession.
Increasing truck capacity to compensate for the longer haul routes.
The extra vehicles caused queues at a pinch point and reduced the throughput of the logistics.
Optimizing the haul roads and adding passing places to avoid traffic bottlenecks.
Without simulation, the three conflicts would only have surfaced on site – one after another, in the middle of the running possession. Each solution would have had to be improvised on site and would have triggered the next conflict. If a possession overruns, the line stays closed longer than planned: trains are cancelled or diverted, and unfinished work cannot simply carry on the next day – a new window has to be planned first.
How does construction process simulation safeguard a short track possession?
In a short possession there is no room for delays, rework or time reserves. The simulation reproduces the planned construction process digitally in advance, using the real output data of the machines, the site environment and the site setup drawings. This makes it possible to check before work starts whether every construction phase fits into the window. At the Else railway bridge, this is how deliverability within the 55-hour possession was proven – and on site, the possession was met.
What kinds of conflicts does a construction process simulation reveal?
It makes spatial and temporal conflicts visible before they arise on site. Spatial means, for example, that an excavator cannot reach its working area or that transport vehicles queue at a pinch point. Temporal means that longer haul routes stretch the process until the possession would be overrun. At the Else railway bridge, such conflicts were resolved in project meetings and the solutions were then simulated again.
Why are construction process and logistics so closely linked in a bridge replacement?
In a bridge replacement during a possession, demolition, lifting in and launching the new bridge and reinstating the track all happen in one continuous window. Every change to a machine position or a transport route directly affects mass movements and the schedule. At the Else railway bridge, moving an excavator lengthened the haul routes for the spoil, which was compensated for with extra truck capacity. That is why it pays to test construction process, logistics and spatial constraints together in one model.
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