Answer: It is possible, as long as you can direct the runoff away from the pool. You can make sure your raised bed drains well by using river rock as a base, set directly on the concrete (or line the concrete with weed barrier and then dump your river rocks on top. I'm guessing a 3-4' tall raised bed and, as wide as you want; a 6" deep layer of river rock should provide adequate drainage.
Ideally you would make each level about two and a half feet high (for ample root growth area). You can use a 50-50 garden soil/potting soil mix to facilitate good drainage.
Start by making a frame, either from wood or stone. Leave some gaps between the stones or the timbers so excess water has a place to drain (away from the pool). Fill the bottom with a 6" deep layer of river rock. Fill with your soil mixture to the desired level, then set your second row of stones or timbers for your second tier and fill with your soil mixture. Then plant.
Best wishes with your new raised bed!
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