I do provide a nesting site for her
And she know going there to dig everytime so i assumed that nesting site should not be the reason

http://i1361.photobucket.com/albums/...ps0d22qzdf.jpg

All my females except one are relatively young. A young redfoot Tortoise will start with infertile eggs, as she ages the fertility increases with age(assuming mature male present). The infertile eggs will blow eventually, some crack some blow. You can not give them too much calcium, calcium that is not absorbed passes straight through the body. I only give cuttlebone for calcium, no powder. They eat it at there own choice, it's obvious when a female is gravid because they devour the cuttlebone more than usual. Remember I'm talking about redfoots, I not sure if the same applies to the Mediterranean species. I would assume yes but have no experience to back that up. That's Gordons job. Lol.

I should have added, just because they are getting enough calcium doesn't mean that they are absorbing it. Without vitamin D the calcium is passed straight through the body and not absorbed. That's why UVB( the sun or artificial is so important). There's also Vit D in some foods, but I don't know the correct diet for stars.
Also if you feed to many foods high in oxalates it binds to the calcium and passes through the body. An example of high oxalate food is spinach. It's ok to feed redfoots from time to time but not every day.

Just because you have a nesting site, does not mean females will actually lay eggs in it. They can be really picky as to where they lay. Everything has to be just right for the female, temps, soil, heat, etc.
I have female iberas that lay in different places, some in the GH soil, some in the rock hard lawn.. Some try to dig concrete. No two tortoises like the same.
I have provided dug over, moist soil, but my females reject and choose their own place.

Where is your uvb light and those tortoises should be on a suitable substrate not a tiled floor. They can't get any traction on that floor when walking, this will result in deformed limbs, also it's probably too cold on that floor.

I know they are picky but my female like to lay egg in that soil corner during the past few years

Its semi outdoor so i dont have a uvb

How warm is that enclosure and the outdoor temps, what level of humidity do you have. Can you see how they are pyramiding, they should be smooth. This is because they are kept too dry. All these things are relevant to fertile eggs. If a tortoises needs are made then fertility will come naturally.

As she is still quite young I would say it could be she is still growing and using the calcium for growth as apposed to eggs or she could just not be able to produce enough to make a decent shell.
As said above give them lots of cuttlefish or even natural chalk stone if you can get it.
The other thing you could try is to put some cover over the laying area like branches and lay grass over that she might be pushing the eggs out to quickly as she doesn't feel secure.

lovely looking torts - take it not in England, Wales or Scotland..CB