I think burrowing sounds like a normal activity, if your BP enjoys it then it can't hurt to provide more opportunities to burrow, as long as she can still easily access her warm spot and the temperatures are controlled correctly (if there is a UTH, you need to measure the surface temp of the floor of the enclosure to set the temperatures, not the top of the substrate).

This is interesting, I've always kept my substrate thin but now I wonder if I could provide extra enrichment by making the substrate thicker.

A question for both Ash and KMG and anyone else who has a thick layer of substrate - when it comes to spot cleaning is it harder to clean with thicker substrate or and does it require more substrate to be thrown out? How often do you replace all of the substrate?