ARCH - How to model gravel and backfill

[elsordo]

I am designing a house that has a frost protected shallow foundation and I need to model the pads of compacted gravel that are under the footings of the building.

I model the pads as ARCH Structures. However, there is a property that is causing me some issues.

For the material, I would like to say that the material is 3/4 inch gravel. The "material" property of the structure object does allow me to link to an object. But the question is, "Where can I find a materials library that would contain definitions of things like "gravel".

The next issue is how to render the gravel pad in 2d drawings. How do I make the structure look like "gravel"?