I think he'd much prefer something like coco coir... The bricks that you soak. The end result is much like soil that he can dig down into, and it holds moisture really well, keeping humidity levels up.
I used repti bark for my russian, and didn't personally like it. The pieces of bark- for the most part- are too big to pass if accidentally ingested. And it seems harder for torts to burrow in.
I used repti bark in Vladimir's habitat because that's what he was living on at the pet store, but after joining the TF I decided to add some coir/play-sand and I honestly think he likes both [SMILING FACE WITH SMILING EYES]
I like to use Repi bark and mix in the coco coir. 1/3 repi bark and 2/3 coco coir. Just to add in, I see the barks a little dry in your tank... suggest get a bottle spray. Helps maintain humidity. You probably want to ad a lot just so they can burrow. just something to think about.
As far as the use of sand. I wouldn't use it as it is known to cause impaction if ingested. But, as with everyone here, these are our opinions, and in many cases, personal experiences. Best of luck!