This shale has a wonderful property, once exposed to air and moisture, it pops like popcorn. It has joints that help it along. I saw one on the exposure. A fresh exposure like this is always a geologist's dream. Anyway, the retreating shale allows the till above to slump. The recent big slumping was triggered by the guy with the swimming pool just dumping water over the edge, but it would have happened soon.
These guys are releasing the till above by their excavation, but the dry weather should help. Once the armourstone is on with the useless cloth, the weathering can start all over again. The usual cure would be to pin on some steel mesh and use shotcrete to hold the shale. Probably 1-2 metre-long bolts to get by the joint expansion. I don't know how you would support the till which looks like it is ready to go any minute. Perhaps more pinning. Or scaling with the same support as the shale. You would need one heck of a long excavator.
For political reasons they probably can't scale the upper section, since that would take an inch off the property. Better to wait and then give a Gallic Shrug. :)
Addition. I'm just adding this because they are using classic 'castle' construction, which is a rock face filled with rubble. This is fantastic!
Tues. update - still building Hadrian's Wall. It's beautiful. Super hot and dry today, dessication cracks all over the place. Of course, that doesn't mean anything.