Has anyone used a 1:1 slope on railway ballast and sub-ballast? AREMA states "A 2:1 is commonly used" in section 2.1.1.5.2.3 Ballast Side Slope Run (BSS).
Stick with 2:1 for track support. Ballast will typically stand at 1:1, but will ravel with time and will cause problems.
If this is for a slope of any significant height, then you need a real stability analysis since the foundation soils and the overall embankment soils will have a big impact on what will and what will not work.