If it requires GI Surface Detail you're going to be looking at some veeery long render times.
It's actually fairly easy to create a sand-like texture just using very small displacement in a surface layer. Create a new Surface Layer, go to the Node Network view and plug your Fractal Breakup into the Displacement Function input of your surface layer (so it is connected to both this and the Breakup Shader input). Now get down close to the surface - you should already see fairly small scale and rough displacement going on.
The default scale is set to 1 meter for the Fractal Breakup shader, so you'll want to bring that down for "sand". Try setting Feature Scale to 0.1, Lead-in scale to 10, and smallest scale to 0.01. You will also want to reduce displacement height so turn down the Displacement Multiplier in the Displacement tab of your Surface Layer to 0.1 or 0.05. With those settings you will get a fairly decent rough-looking small-scale surface, but you'll probably need to experiment more to get a better "sandy" look. I would disable the warping in the noise shader, for example, and I might reduce variation and clumping as well.
My final settings for scale and displacement were:
Displacement Multiplier: 0.025
Feature Scale: 0.02
Lead-in Scale: 10
Smallest Scale: 0.005 (reducing smallest scale much more will trigger an error in the renderer where the surface renders black)
This produced pretty good sand-like texturing from an average human standing height above the terrain (2m), however it won't be very distinct from greater distances. It's realistic, since you can't really see the roughness of sand from far away anyway, but if you want to force the rough look of sand grains from a greater distance you can just adjust the scales and displacement.
There's a clip file attached.
- Oshyan
