It's like the old false floors they had in computer buildings to enable the free flow of cables beneath them. There are no cables beneath this paving, though, it's just to level out the square. There are little posts made of plastic, of different sizes to raise the slabs to the same level. The old layout was sloped so that near the edges was higher than near the middle, meaning that wainwater would run towards the middle where there was a big hole. There, it would fall into a guttering system and be sent to the drains.
We don't have a big hole in the middle now because they filled it in so they could pave it over. The slabs here are raised several centimetres, whereas some of the slabs at the edges aren't even raised at all. As you can see from the photo, though, whatever rainwater solution they intended to have in place doesn't work. The water pools.
Also, although the theory of raising all the slabs to the same level sounds solid, in practice the heights of the various posts can't be adjusted with enough fidelity. Many of the slabs rock, like a table with one leg shorter than the other. There's no cement between them, they're all independent. I thought that perhaps the idea was the flood the whole square with cement once the slabs were in place, but this isn't the case. The plan seems to be that enough usage will cause wear on the posts and make them settle. That doesn't deal with the water that's sitting beneath them, waiting to act as a breeding ground for midges and mosquitoes in the summer.
The result of this is that when we walk across parts of the square, particularly right near the entrance of the STEM building, the slabs squelch.