Underground engineering

Fast Road "Licodia Eubea - Libertinia"

Completion section between Regalsemi junction and State Road 117 bis (Gigliotto junction)
Owner/client ANAS S.p.A.
Type of service Detailed Design, Final Design Assistance
Location Province of Catania
Period 2016 - 2018
Cost € 94.000.000

PRO ITER Prog. Infrastr. Terr. (principal); Delta Ingegneria (mandatary)

The intervention is included among the works planned for the Strada a Scorrimento Veloce No.683 "Licodia Eubea" completion and in particular of the Regalsemi - State Road No.117bis junction (Lots 3.1 & 3.2), from Regalsemi (km 0+000) to the beginning of the Caltagirone bypass (km 3+700).

The new road system (secondary suburban road type C1 with a 10.5 m platform, two 3.75 m lanes and two 1.5 m external platforms) is hinged on the two junctions at the beginning and end of the lot, with intersections resolved at staggered levels. After an initial section in which the 'Regalsemi' viaduct (470 m) is planned, the intervention is characterized by a route substantially in trenches, with supporting works composed of piles bulkheads and plating walls for the land consumption containment and the two important underground works construction (the natural tunnel 'Santa Caterina' of 900 m and the artificial tunnel of 130 m).

The study of the Regalsemi viaduct and its junction branches has been set up pursuing the following objectives:

  1. Simplify the decks construction technology, while still ensuring the work aesthetic-architectural value.
  2. To improve the works durability with consequent maintenance costs reduction.
  3. Uniforming solutions to the works of the already completed adjacent Lot.

The main viaduct (470 m long), with its two interchange ramps, is built with mixed section steel-concrete decks and in-situ cast slab with variable width, in order to manage the widening for the deceleration lanes and for the free views. The structural scheme is a continuous beam with 2 beams in order to contain the carpentry incidences and simplify the launching and construction; the beams number increases from 2 to 3 only on the main route in the enlargement stretches, with the transverse and torsional stiffeners inclusion. The work has a ratio section height to span equal to 1/27, in order to ensure visual transparency for the landscape. The piers have been designed with an elliptical section with top pulvinus, maintaining the hollow section concept: this choice is appropriate to reduce the structures inertia and contain the seismic masses entity.

'Regalsemi' viaduct

Total length 470 m, with 2 interchange ramps.

Natural tunnel

Santa Caterina" tunnel, 900 m long.

Artificial tunnel

Gallery total development 130 m.

The single-tube 'Santa Caterina' tunnel is located near the Caltagirone residential area and extends for about 900 m (760 m in natural tunnel under the mountain and 140 m in artificial tunnel). After an artificial tunnel section of about 60 m, the infrastructure continues in open air at the North entrance side and ends with a trench section between bulkheads on large diameter piles at the South side; this is followed by 80 m of artificial tunnel, completely underground to reduce the landscape impact.

In compliance with safety requirements (ANAS Guidelines 2009), the tunnel has two escape routes 300 m apart and at each entrance. The area morphological context directed the design towards the choice of two escape routes with separate routes, 34.5 m and 332 m long respectively. The escape routes exit at their respective mouths at a single square. In general, the work has a reduced coverage (with a maximum value of 30 m) and is inserted in a surface context characterized by the presence of some houses along the route at a variable distance from its axis; moreover, it crosses mainly sand formations with calcarenitic levels and, at times, marly clays. The water table level is usually found below the excavation of the inverted arch, with some stretches higher up to the height of the walls. Considering the geological-geotechnical context, the contained covers and the presence of numerous buildings, the project has provided for stabilization and consolidation interventions (mainly with jet-grouting columnar treatments on the cap, the piers and the excavation face). Where the contact between the argillitic and sandy units moves towards the cap, the jet-grouting columns (which are not very successful in clayey soils) were replaced with metal and/or fiberglass elements. The length of the advance field from 6 m , 9 m and 12 m, characterizes the different sections of excavation and consolidation. The different typological sections were applied along the axis in order to ensure proper stabilization and limit surface subsidence. For the construction phase, both inside the tunnel and on the surface, constant monitoring of deformation parameters and settlements was foreseen, together with the corresponding potential effects on the buildings present (risk analysis procedures for buildings). Attention and warning thresholds have been identified which, if exceeded, trigger specific countermeasures already planned in the design phase (following the development of scenarios and risk analysis).

The entrance works were the subject of an in-depth study of the implementation problems, since the low slopes of the slopes, in correspondence of which the attack of the natural excavation takes place, has determined the adoption of important bulkheads, necessary for the artificial tunnels entrance construction: in particular, for the North tunnel portal was chosen a solution to 'flute beak' extremely effective from the architectural point of view, able to allow a better masking of the structures compared to the landscape context.

Constant monitoring is foreseen during the construction phase (inside and on the tunnel surface) for deformations and subsidence, together with potential effects on the existent buildings, with attention and alarm thresholds (if exceeded, specific countermeasures already planned during the project phase are triggered).