Delete Mesh based on Particle Velocity

[Adam_28798]

Im having trouble with the delete by expression. I have a mesh which is wet sand, however i want it to start as the solid mesh and convert into the particles when they get awaken by the collision geometry.

What would be the best way to achieve this?

[bunker]

you can create a point group based on velocity in a attribwrangle node
if(length(v@v)>chf("speed_threshold"))@group_particles=1;

or just delete the particles directly:
if(length(v@v)>chf("speed_threshold"))removepoint(0,@ptnum);