Mine Gianna: a jump back in history

To assure the unstable blocks of rock they inserted " tie-rods" similar to nails, at the end of which an umbrella opening device granted the anchorage of the block to the wall. They were fixed outside with iron plaquettes.

The currently used models (Swellex) exploit the same principle but they are inflated, and expanded thanks to a jet of pressured water once they are turned on. Thus traction is exerted from inside the tie-rod.