I had gall bladder surgery 10 days ago, 4 day postop I started gritty sandy bowel movements loose large. I never had this before, concerns?

Here are some ... I wouldn't worry about it as long as feeling better day by day in general activity, appetite, voiding, BM, etc. with no fever or undue pain. Of course, if not as described or something mentally or physically bothering you, ask your surgeon timely. Note, after gallbladder removal, your body is adjusting to the "new" environment without a gallbladder for digestion so to expect slight change in BM.