Lots of photos in yesterdays papers about the burst 32 inch water main in London and the effect on an underground carpark.
For those who didn't see it (or hear the Jermey Vine phone-in), this was reported as 'polystyrene expanded after being submerged by a massive flood). I think not !!!. Do people not know about buoyancy these days ?, or the reason why massive metal ships don't sink ?.
The upwards force of the water was sufficient to lift the carpark floor and the vehicles parked thereon, jamming them into the ceiling. There seemed to be an awful lot of EPS under that floor. It cannot have been there as a thermal insulation (car park), so maybe there was a problem with the soil. Or maybe the builder had a load of EPS left over and wanted to avoid disposal fees. May be the builder bought the EPS and was told by building control that it was the wrong stuff - get rid of it ?.
There used to be a website hosted by TML the chunnel builders, and how they built the Sangatte side. Essentially this is a massive concrete-lined hole, presumably below the water table, and to stop it popping back up, something like 160,000 tons of concrete were poured to cover it.