jb, they may be cutting out the roadway to reduce the incline, leaving the hillside along the shoulder, well off of the road surface. I can show you places down in SW Missouri, NW Arkansas where the road surface passes between shear rock walls forty to fifty feet high, and similar angled bore holes are clearly visible top to bottom. Drill, excavate on one side, then start shearing off the rock in sections. Don't know if they may use small, precision directional shots to speed the process, but I could get the full story with a phone call.
Here's a picture of a deep, terraced cut as an example of what I think you may have seen. Not sure of the location....
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