Roads & Motorways

North-West Road bypass of Merano (Lot 2)

Road Tunnel in urban environment
Owner/client Consorzio San Benedetto Scarl
Type of service Construction Documents
Location Merano (BZ)
Period 2020 - present
Cost 100'000'000 €

Merano's Northwest Ring Road (Lot 2) is a project of the Autonomous Province of Bolzano (amount of work about € 100 million), which completes the freeway in and out of the city center and connects the existing Bolzano-Merano freeway to the west and the Passeiertal route to the east, continuing the penetration axis of Lot 1.

The route of Lot 2 starts in the northwest area of Merano, in continuity with Lot 1, already completed and currently in operation, runs eastward under the city and Mount St. Benedict, and then connects to the existing Passeiertal route. Except for the open-air sections to the east, Lot 2 consists mainly of a single tunnel with a total length of about 2200 m, which can be divided into two parts: an initial section of Artificial Tunnel (L=136 m), connected to Lot 1 and the surface road system, and a subsequent section of conventional underground excavation (L=2064 m). The latter, for approximately the first km, runs through the city of Merano and is characterized by the presence of loose soils and reduced overburden; moving eastward, the tunnel crosses the metamorphic rock formations of Mount St. Benedict, with overburdens up to about 100 m.

Artificial Tunnel

Length 136 m, connected to Lot 1 and the surface road system

Natural Tunnel

Length 2064 m, in the presence of loose soils and low cover

Underground traffic circle

Diameter 42 m, supported by a central rock pillar

The loose soil consists mostly of silty sands with modest cohesion in the uppermost portion (about 2÷4 m) and underlying gravels, sandy gravels, and gravelly sands (alluvial deposits of the Adige, Rio Nova, and Passiria rivers), with pebbles and frequent bedrock, generally less than 1 m3. The water table is situated about 20 m above ground level and may interfere with the lower part of the tunnel structures.

The main geological peculiarity of the rocky part of the route (with geomechanical class varying between classes III and IV of the Bieniawski rock mass classification) is the crossing of the Periadriatic Lineament, here called the Merano-Mules Fault, which separates the Bressanone Southalpine Unit, consisting of cornubianitic phyllites (due to the nearby Permian granodioritic intrusion), from the Marlengo Austroalpine stratum, with a predominance of often cataclastic gneisses and mica schists. Where tunnel excavation involved contact with the Merano-Mules fault, recrystallized milonites were found in ductile condition, with a fair amount of self-supporting capacity.

The standard section of the tunnel has a two-way roadway, characterized by 2 lanes of 3.5 m, two 0.75 m side berms and two sidewalks of varying widths for a total internal width of 11.8 m. The roadway platform widens at the 4 lay-bys provided along the route (2 in the rocky section and 2 in the loose soil section) and in the sections housing the entrance and exit lanes: on the approach to the east entrance (platform width = 15.1 m) and in the first section west of the Natural Tunnel (platform width = 15.5 m). In particular, the Artificial Tunnel to the west accommodates two ramps, one entrance and one exit, whose acceleration and deceleration lanes affect the first section of the Natural Tunnel for a development of about 160 m, resulting in a significant increase in the width of the road platform (up to 15.5 m) and consequently in the excavation area of the section, which increases from about 150 sqm (L≈15m, H≈11m) to about 240 sqm (L≈21m, H≈13m).

About one kilometer from the east portal, an underground traffic circle with a total diameter of about 42 m, supported by a central rock pillar with a diameter of 8 m, is planned to provide access to the future underground parking lot at Monte San Benedetto.