In order to strengthen and reinforce the rock mass at the tunnel’s excavation perimeter, a rock reinforcing system that combines stainless steel rock bolts with flexible netting has been selected and dimensioned. These measures allow also viewing of the geological conditions along the tunnel, which can be considered as a “geological museum” also. Rock bolting capacity, length and installation pattern have been adjusted to the rock mass conditions along the tunnel. The same holds for the stainless - steel netting as far as the net’s diameter and net’s cable spacing is concerned
At locations of significant cave-ins the tunnel has been also protected by a stainless steel canopy made out of steel sets and girders. At the cave-in behind the lining at the north exit portal, the netting was replaced by a reinforced concrete layer. At this location, the tunnel’s lining protection measures also include careful removal of the failed rock material that accumulated behind the lining’s arch, strengthening the arch with neutral grouts and filling the space between the arch and the cave-in’s perimeter with bags filled with lightweight material.
The archaic lining suffers serious damages at certain points along the tunnel. In particular, the key stones of the roof suffer significant convergences, distortion and fracture. In another case the sidewall of the tunnel is significantly deformed due to horizontal earth pressures. At these locations the results of the geophysical survey identified weak fault zones in the vicinity of the lining. The protection/restoration measures that were dimensioned include: a) staged dismantling of the lining stone by stone, b) supporting the ground behind the lining using rock bolts, steel sets and a concrete mantle, c) rebuilding the lining at its original position before the failure. The measures previously described are the most significant ones. Other minor measures include spot bolting, minor nailing and local grouting.