Abhishek,
I have no idea whether the shells were empty or not as I didn't go close to the nest. I guess from the sound of the shells when the bee-eater was tossing up the snail shells, those might be empty.

Saktipada ji,
After digging, their beaks get fairly worn out. I did a lot of secondary research ie. reading existing papers on bee-eaters. I have now found one reference online about such behaviour of swallowing snail shells for calcium needs. Trying to get the original paper. Video recording the complete behaviour has helped, else people would have said that the bird was playing with the snail shell.

Cheers,
Sabyasachi