One such place is the Parc du Cinquantenaire. If you happen to be sat on the grass, perhaps enjoying a waffle and looking up the hill towards the Arc de Triomphe, you could be totally unaware that below you are four lanes of road traffic thundering past on the N3, silenced by the concrete roof of the Tunel Cinquantenaire and many many many tonnes of soil.

The only thing that might give a hint as to the city’s hidden underground transport infrastructure is the rumble below your derrière as the city’s subway trains shuttle the city’s residents east and west between Schuman and Merode stations.

Perhaps more surprisingly though, is that you can hear these trains in the park. Yes, like the road, they are also buried under tonnes of earth and run in a concrete tunnel, but the vibration they produce resonates through these to the surface of the park, which then radiates it as sound, much like a large-scale loudspeaker.

It’s initially quite a strange sensation to experience a snippet of the city centre bustle in an otherwise tranquil park, but it serves as a reminder of the engineering feats that we often take for granted in modern cities.

This is exactly what also happens in buildings on top of or next to rail lines and it’s why, at very early stages of developing a site, our clients engage with us to establish what risks the vibration from transport might pose to the scheme.

Building over rail lines has the potential to provide in excess of 250,000 homes in London alone – something we’ve previously written about here.

In some cases, protecting dwellings from the risk of vibration can be costly, but with the right advice, starting from an early stage in the design, that cost need not be prohibitive.

Historically, predicting vibration has had inherently high levels of uncertainty, and many analysis techniques were developed before modern high-rise buildings were commonplace.

That’s why, at WSP, we’re investing in time and in research. And in the latest vibration measurement and prediction methods.

And we’re collaborating. Between our specialist teams. With industry and with academia.

Whilst we still use traditional calculation methods to scope the level of risk; by using sophisticated computer modelling we can refine and tailor our assessments to match the site conditions and the needs of the project. Quantifying the risk more precisely reduces reliance on safety factors.

Crucially, modelling a building’s actual structure allows us to investigate ways of changing its response to vibration and widens the range of mitigation options at our clients’ disposal.

By developing more cost effective solutions to vibration, we are able to unlock hidden value in parcels of land that might otherwise by left untouched, or at least only suitable for less profitable development.

This blog was written by Robert Marriner, WSP Acoustics Associate.