I wonder how thick you need to make a coquina wall in order to prevent a cannonball from that era to go through. I guess not having it thick enough can be dange

I wonder how thick you need to make a coquina wall in order to prevent a cannonball from that era to go through. I guess not having it thick enough can be dangerous as the inner layer of the wall might work as shrapnel and hurt anyone on the other side. I know some tank shells worked on that principle before they added some kind of liner on the inside.