Sand is far more predicatable than volcanic ash since it's constituents are less varried. With that said here are the engine concerns:
1) Sand accumulation in the oil system or cooling air holes in the hot section
2) erosion of the spinning blades
3) melting of the finer particles (if there are any) in the burner and redeposition on the turbine nozzle vanes.
4) Inability for the engine to respond to throttle increases
Items 1) and 2) are long term concerns and would likely only manifest themselves over several flights.
Item 3) & 4) are the chief worry for both sand and especially volcanic ash.
sand is much less of a concern than volcanic ash since its particulate size (grains) often are much bigger than some of the volcanic dust that reaches high altitudes and therfore it doesn't have enough time to melt in the burner. Couple this with the expected low turbine inlet temperatures of an approach, compared to takeoff or cruise and it's unlikely that sand will turn on the concerns in items 3) & 4)
I would be a lot more concerned about gross sand ingestion in a takeoff situation.