Berliner construction for access to existing tunnel

The surgery was performed at the A2A hydroelectric power plant in Grosio, where the replacement of the high voltage cable support poles.
The new poles were to be positioned at about 3 metres distance from the existing ones, which, however, could not be removed before the new supports were installed, as they were still active in maintaining the line.

The main complexity of the intervention stemmed from the fact that the foundations of the new piles fell exactly at the top of a service pedestrian tunnel below, connected to the power plant. To ensure the stability of the ground and structural safety during excavation and replacement, it was necessary to build a containment Berliner close to the existing poles.

The Berliner, consisting of a series of vertically arranged micropiles connected by two metal crowning beams, It had the function of supporting the ground and preventing subsidence or deformation in the area of interference with the tunnel. This temporary support system ensured the full stability of the site during the excavation operations and the installation of the new structural elements.

Once the Berliner was completed, excavation proceeded until the top of the tunnel was reached, on which two Ø 1000 mm cores. Prefabricated piles were inserted into these holes, which were subsequently stabilised by pouring concrete directly from the shaft to form the foundation of the new piles.

Once the installation and consolidation of the new posts is complete, the power lines were transferred to the upgraded plant, allowing the existing piles and foundations to be safely removed, completing the work without interfering with either the functionality of the power plant or the stability of the existing works.