Is he doing this in the morning? This would be called the morning stretch and it is normal - it could also be hes getting ready to shed his beard--- they all do it -- the sand I would get rid of it can cause impaction and it harbors bacteria
DO NOT use sand, shavings or any other loose substrate for baby to juvenile beardies. They can be very clumsy eaters and they are also very curious and like to taste everything. Any kind of loose substrate holds serious health risks to your Beardie. If they eat a loose substrate they can become impacted, which is a blocking of the intestines, and die.
Crushed walnut shell is dangerous and should only be used to clean up oil spills. This substrate is NOT digestable and if too much of it is eaten it will cause impaction. I have seen this occur first hand with reptiles ranging from lizards to tortoises. Stay away from this product please.
I would get some paper towels in there for now and look into getting some textured NON adhesive shelf liner from Home Depot or some slated ceramic tile w/ texture NO corse if your tank is the permanent one meaning your not going to upgrade ---
Karrie