Access to the underground workings at the La Camorra mine is via a ramp from the surface, excavated at a -15% grade and connecting numerous levels.
Mine ramps are excavated at a -15% grade
This one has ramps excavated at a -15% grade. That doesn't mean every single mine does.
( z1 excavate :ARG1 ( z2 ramp :mod ( z3 mine ) ) :location ( z4 grade :mod ( z5 percentage-entity :value 15 ) ) )