With possession orders often limited to 24 hours, time is an important factor in rail projects, especially when you are building a bridge or a platform. Manufacturing components, such as pre-cast platforms, canopies and modular plant rooms offsite, means that only the installation has to be done within the possession order. Standardising, componentising and developing design features, such as crossing points and switches for offsite construction, massively reduces the time on site and so the disruption to passengers.
Due to the nature of live railways, construction sites that are on or near them are often constrained and therefore even more dangerous for workers and the wider community around them. In addition to minimising disruption, offsite also helps to keep passengers, railway staff, site workers and lineside neighbours safe by optimising the physical footprint of a construction site, and reducing the amount of time it is in operation. It also means there’s time to give more consideration to aesthetics – an important consideration in station environments, where components are on show to the public. Offsite lends itself to creating decorative and precast brick panels, for example, while also more easily ensuring robustness and quality.
Integrating more processes
But it’s possible to do more still with offsite. The construction industry has been relatively siloed; if a company produces a wall system, traditionally that’s all it does – it won’t necessarily integrate MEP, insulation or windows into that wall. Why not manufacture them all into the same component at the same time?
For the complex transformation of London Bridge Station, in which WSP was involved from the outset, we considered the advantages of offsite early on in the construction planning phase. This enabled us to push the boundaries of offsite to keep station closures and service disruptions to a minimum. In fact, we managed to ensure only three out of 15 platforms were closed at any one time over a 5-year construction period.
This was down to innovations such as manufacturing modular canopy components with structural elements, architectural finish, acoustics, waterproofing and MEP services all built in. One key benefit of combining all these processes into one component was that installation of the canopy progressed much more quickly – at 50m per week.
Expanding the opportunities
Taking this approach can feel like a big leap. But ask yourself: “What would happen if, instead of having four contractors lift in four components made offsite, we manufactured everything into a single component and installed it in one go?” It may not always be possible, but where it is, shouldn’t we be capitalising on the benefits?
Offsite often opens up other possibilities for linear infrastructure, such as rail and road projects. The Linear Infrastructure Overbuild Guide which WSP helped produce looks at how to make best use of the space over these assets, which is often forgotten about. Offsite is a key enabler of making the most of this opportunity by enabling construction in historically constrained spaces and releasing value for asset owners.
Designed in from the outset
This is a process we help to steer our clients through – identifying early in a project whether, and how, offsite could help them achieve their objectives. Considering offsite from the outset is key because if, using our in-house tools, we identify opportunities for using offsite then we design it in from the beginning. Every decision we then take – from material choices to sizes, weights and tolerances – is designed to make the most of offsite.
Designing a project around offsite in this way also opens new possibilities.
I think this shows that, while it’s certainly not right for every situation, offsite still has untapped potential.
WSP Author:
Richard Anderson - Technical Director, WSP
