If you go back to the 6/6/2002 imagery, I think they are laying some sort of geotextile under the new taxiway.
There are way too many types of these fabrics for me to even guess what type they are using. The fabric is expensive, but the base ain't going
anywhere. So if the taxiway lasts longer, the extra cost makes sense. When they build developments in hilly areas, you often see berms that are
steeper than 2:1. They use layers of geotex sandwiched between dirt to make it possible to do such steep embankments. It pays if you can build more
houses in the development.