The cause of pyramiding is caused primarily by conditions that are too dry when the tortoise is small. Overfeeding may contribute if the offered items are not balanced and low in calcium.
The dry look to your animals is also caused by low humidity although adult animals as well as juveniles all look better when their shells are actually wet. Try to be sure that they have a humid area in which to hide at night and during the heat of the day. In the wild they seek out vegetation piles or mammal burrows and in these situations the humidity is much greater than the outside air.
Also, make sure that they have access to shallow water always.