Do you not already have a substrate in there?
Have you read this care sheet?-Russian Tortoise Care Sheet https://tortoiseforum.org/index.php?threads/Russian-Tortoise-Care-Sheet.80698/
Coco coir, peat moss, orchid bark, and cypress mulch. He needs 4+ inches.
Keep in mind that he could also be banging against the walls because his enclosure is too small. How large is you’re enclosure?
Your enclosure is much, much too small for an adult Russian, and I’m assuming you’re using the zoo med tortoise house. Your tortoise needs a minimum enclosure size of 8x4 feet, which is why he’s banging against the walls. The substrate needs to be at least 4 inches deep.