Interesting stuff, as was the earlier thread along a similar line.
A couple of questions if someone can help.
1) Does anyone know if XGD has been used in the UK?
2) I've heard of a method called I think, vertical drainage - where you drill down right through a push-up style clay-lined green with a 6 inch size bit. This is apparently done in a pre-determined spaced pattern all over the greens surface, maybe up to 100-300 times, and then the holes are lined and back-filled with a porous material. Has anyone heard of this or tried this approach and if so was it successful?
All the best
I'm not sure if XGD, the company, has done work in the UK but I believe some clubs there have used a similar method.
I have heard of a vertical drainage type system you describe (possibly in fairways/roughs) but don't know anyone who has done it, or for that matter, why they would do it on greens, as the disruption to play would be huge considering how long the holes would take to heal.
Saying that, it is very similar to the drill and fill process which uses ~1" dia bits so the turf can heal reasonably quickly. Drill and fill works best if there is a free draining medium under the green soil or in addition to drainage like the XGD system as otherwise you run the potential of creating a bath, where the water will fill the hole but has no where to go.