50 sand 50 top soil I say, can't go wrong.
I have a tropical tortoise (elongated) and I keep her on the same and she's happy.
I compact it down and sink a bathing pool in at one end and some slates (etc around it and to help avoid sand/mud going into the water) for claw wear and tear. A hide box is positioned at the opposite end to the water to initiate some exercise etc. Every night if she isnt back in her box I place her in it to train her to sleep there.
hope that helps. the main thing that i have found that seems to differ between tortoise species is diet and temps. habitat set up and substrate seems be quite general across the board. but check the tortoise trust website, its excellent.