Is it really "splitting," or is it just not tough enough to support the contents of those delicious looking little hand-pies there? It looks like it might be great (tender and delicious) for a pie in a pie-pan which doesn't need so much structural strength.
I think this dough is too short & delicate and/or rolled out too thin for this purpose. It would provide more support if you either added a little more flour and water (proportionately -- in other words: less shortening), worked it a little more to develop a little tougher gluten, or maybe simply rolled it into a little bit thicker sheet. I bet it won't be quite as tasty if you do that, but might be mechanically a little more effective.
Also, I'm not 100% clear on the sizes in the photo, but perhaps the dough could work better as-is if the pies were made a little smaller, ... if that is feasible at all. Since I guess pies scale like other things; the bigger they are, the less delicate they can afford to be.