Mysterious Eurotunnel structure on A20, Kent

[Class999999]

Whenever driving to the port of dover, on the A20, in the samphire hoe area, I noticed a strange little turnoff, to the north, appears to be a highly secure structure with camera fencing etc. Is this another ventilation shaft for the channel tunnel, or does anyone have any further information on it?
The site its on appears to have been part of a much larger car park during channel tunnel construction.

Map coordinates:

51°06'37.9"N 1°16'43.6"E​

Google Maps Link:
Map Link

 

[jfowkes]

OpenStreetMap is great for this sort of thing. Has lots of detail that Google Maps doesn't care about.

It's a ventilation shaft: https://www.openstreetmap.org/#map=19/51.110305/1.278791

This picture on Geograph may show the ventilation shaft under construction, it's a bit hard to match features on Google Earth/street view precisely to this photo. But it looks about right...