Yeah, I acknowledged 1:1 for excavation in a comment up a couple levels. That said, where are you that 3:2 is a standard slope for unreinforced permanent slopes? That's 34deg, which is outside the angle of repose for many materials, and doesn't leave much factor of safety even for a crushed stone.
Reinforced earth is a different beast altogether for sure.
Yep, it is the the typical slope for earth moving, Italy here, thousands of km of roads are made with this slope, exceptionally it is lowered up to 4:1, a reference:
What I mean by 3:2 (base divided by height) is often referred to as 2/3 (height divided by base) and is roughly the "natural" angle of repose of - say - gravel.
Thanks for the reference. It's interesting that they work that close to the stability limits without just adding some slope reinforcement. It doesn't leave much room for error (execution error, erosion over time, unexpected surcharge load, stability changes with soil saturation, or earthquake).
I towed my sheepsfoot roller around with a big Italian Same tractor in the
1980's, in West TN. We had those for the ground speed PTOs but they
climb things like mountain goats, unique to the market at the
time, which enabled some of the stupid tricks we built.
By comparison to their source, our hills are pleasant soft
sandcastles, all rubbery clays with veins of sand or gravel and never
any excuse for explosives.
Reinforced earth is a different beast altogether for sure.