Grain sim thickness + underwater gravity

[smallbird]

Hey,

Super new to Houdini here. Trying to stray away from my comp education and go into FX instead.

We just finished a group project and it's time for summer break so I want to go back and do FX for a couple of finished projects of other groups to get finished comped shots to build a FX reel.

For this particular project I wanted to make a grain simulation for a group that had a hermit crab switching his shell on the ocean floor. The finished project contained just a mesh with a sand texture on it together with stock footage for some dust and smoke when the crab flips the new shell from the sand bottom.

I have attached my super quick way of re-doing it by following mainly a tutorial about the grainsource/grainsolver adjusted to this scene. My further a long hip is not that much better off anyway and much messier with much trial and error.

Main problems are;
-The particles keep moving for such a long duration even though I have friction parameters set to 1. Maybe the sim just have to run much longer?
-Size of particles to represent sand obviously has to be quite tiny so I'm a bit unsure if I will have to scale them down all that much and create a super thick layer that covers all the way down to the tip of the shells flip animation (at ~54F) that to me looks like I'll be in the millions.
-Camera seems off. I was reading up about camera exporting from Maya and asked a former student at my school that has been at an internship working with Houdini that said Null scaled to .001 is fine but it doesn't match the final shot. I will also have to double check this with the group that provided me with the assets. Still nice to get clarification.
-Underwater gravity for the stones. I assume transfering Cd to the particles getting hit by the shell and then add a POP Force group that lowers the gravity specifically for those particles?
-Maybe not such a big issue but particles clipping on the ground plane.
-I also don't seem to be able to give the grains a shader/material like in the tutorial I watched. I have no idea what I'm doing wrong here. Just adding a dirt slaps it in /mat and gives it to everything except my particles. Although that works when doing the dop import afterwards when everything else is removed anyway.

I have attached the hip file a long with the assets I have received from the group.
 

cstSand.zip