I was shown a a reference image of a ground at a gun range, and decided to experiment with creating something similar.
The shells themselves took a bit of time to get something I liked (note: such crazy rotations on the shells was a design choice). I started off using a tile sampler colour to try and avoid intersections, but I didn't quite get the result I wanted. I then tried multiple samplers, scattering around shells without overlaps and "layering" them by clamping the height values of each layer, but again, the results weren't too great.
I settled on doing this external, by creating a tileable in Autodesk Maya, and baking a heightmap in Substance Designer. I then transformed/offset and blended another version of the heightmap to fill in a bit more of the space and have some sitting lower into the dirt like they've been there for some time.
Everything else (Detailing, Dirt/Rock, etc) done in substance.
References from: https://gum.co/pEphp