I've never noticed this happening. Is it possible that an animal is rubbing against them and causing them to split? Are they also being pushed over? My dogs just romp all over everything, even when it's blooming, like they have no sense at all. Cheryl

Where is the split happening? If it is at the base of a fan on the outside leaves this is normal. The rhizome is growing quickly and the old leaves do not grow along with it - they just die back, but before they do that they split at the base as new leaves emerge.