One thing I noticed from the updates they keep putting through the letterbox is that they are using a vacuum technique to excavate the slots for the "membrane walls," the reason being that they want to avoid damaging "essential services"
The whole area has been a railway shunting yard since the middle of the 19th century, so exactly what "essential services" might be underneath it is somewhat difficult to imagine. But it occurs to me that something that avoids damaging "essential services" may also score high on the "not setting off any WW2 bombs that might happen to be around" criterion. This area was VERY heavily bombed during WW2 - my relatively short street took two bombs, a large area on the other side of the railway was pretty much demolished, and the tracks and Paddington station were VERY high-priority targets.
Hopefully I'm wrong, but it wouldn't astonish me if something turned up while this is going on.
Meanwhile, I had to take the underground this evening - here are a couple of pictures I took from the platform of Royal Oak station.
Looking East towards Paddington Station from Royal Oak, I think the red tanks are cement and some sort of gunge that's used to fill the slots temporarily while they are being excavated.
Looking west towards the area opposite my house, some of the construction equipment that's currently being used to excavate etc.