I now know all about vibro piling. It's highly sophisticated, computer controlled, made in Preston, and here is the rig (above). One of apparently two such units in the world was on the Lower Mantle Close site today, and I got a guided tour. I'll be going back tomorrow to see it doing it's business. It's working on ground stabilisation (most of the site is made ground) prior to starting work on new workshop units. See http://vibro.co.uk/