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The project of the Castello tunnel

Draco technology is used for the structural consolidation and waterproofing of the castello tunnel on the A14 motorway at Grottammare

tunnel

Castello tunnel    Per la versione in Italiano: https://www.stradeeautostrade.it/gallerie-e-tunnelling/il-progetto-di-intervento-alla-galleria-castello/

In August 2018, a fire started by a heavy vehicle inside the Castello tunnel at Grottammare on the southbound carriageway after the North entrance to the tunnel, in the stretch of the A14 motorway which goes through the Marche region, caused major damage, including structural damage aided by ventilation fans, the fire spread from its point of origin towards the North entrance, generating, at its peak, a sudden increase in temperature which irreparably damaged most of the concrete lining on the tunnel intrados.

The damage also extended to the portal at the South entrance, which developed a crack which was more than 6 m long and the thickness of the concrete, jeopardizing the stability of the structure.

The tunnel also had significant, widespread infiltrations from the soil around it, with water inrush in some places.

tunnel
1. Positioning of the ribs and connection at the crown by steel sheets

Following the incident, top priority work was carried out which involved “armouring” the tunnel with ribs placed 100 cm apart, calendered on the extrados profile of the tunnel; the ribs were connected at the crown by steel sheets to prevent fragments of concrete falling and with chains on the abutment walls.

The work meant the tunnel had to be reduced to a single central lane, separated by jersey barriers, causing considerable disruption to the traffic which is often heavy along this stretch of motorway. 

The project

To ensure the tunnel was permanently safe, it was decided to consolidate and waterproof the concrete and soil behind it by injecting resin, removing and milling the damaged top layer of the concrete lining and replacing it with a layer of fibre-reinforced sprayed concrete.

  • tunnel
    2 draco
    2. Exploratory coring and hole drilling for packer installation
  • tunnel
    3 draco
    3. Execution of the tunnel lining

Following a visual inspection carried out immediately after the fire, sample concrete cores were taken from the lining and uniaxial compression tests performed. In light of the results and the considerations that emerged, the work was divided into two sections: the first 30 m of the tunnel, which had not been overly damaged by the fire, and a second section of 120 m, which had suffered significant damage and had to be made safe by armouring with ribs and sheets.

Other work involved rebuilding a piece of the sloping portal at the North entrance of the southbound carriageway and consolidating the portal of the North entrance, again southbound.

The waterproofing of the tunnel extrados

The preliminary work involved exploratory coring every 80-100 cm on the intrados of the concrete wall to verify the extent and depth of the infiltrations and making holes to house the packers.

The core samples made it possible to find voids unevenly distributed between the concrete wall and soil, more at the top than at the base of the arch.

The Engineer decided to waterproof the arch using two different injection systems: a first one based on acrylic resins at the arch haunches, due to higher flowability and penetration capacity, and a second one based on polyurethane resins at the crown because of higher swelling capacity and lightness, which is ideal for filling voids and stopping water inrush without increasing the load applied on the arch.

tunnel
4. Hole drilling for packer installation

The steel ribs protecting the lining defined the injection areas and spots where the holes for the consolidation injections had to be drilled according to a scheme that envisaged a hole every 100 cm lengthwise to the tunnel and every 60 cm crosswise. Holes had to be at least 120 cm deep so as to cross the concrete lining and shotcrete layer on the back, and to penetrate the ground by at least 20 cm.

The resin injection at the arch haunches

After cleaning the surface and removing the existing mesh and cement-based mortar layer, holes were drilled radially according to the project design.

The packers were placed in the holes and secured using fast setting mortar Hydroplug. Dracogel GT2, a water-swelling acrylic resin with adjustable gel time (the resin has a variable gel time from 5 to 10 minutes at a temperature between +2 °C and +18 °C) was then injected into the holes.

Since it uses water as its permeation medium and is a single-phase product, Dracogel GT2 penetrates extremely well and, thanks to its low surface tension and very low viscosity, it can consolidate even loamy soils with a particle diameter as small as 0.01 mm. Voids and holes are filled with Dracogel GT2 which solidifies to form a strong gel that prevents the passage or leaching of water from the environment.

  • tunnel
    5A draco
    5A. Packer fixing with acrylic water-swelling resin
  • tunnel
    5B draco
    5B. Packer fixing with acrylic water-swelling resin
The polyurethane resin injection at the crown

Starjet AC packers – 16 mm diameter steel injection packer for concrete, suitable for high pressure (> 3 bar) – were installed in the top holes and secured using fast setting mortar Hydroplug, a cement-based binder that is mixed with water to create a thixotropic mix easy to apply both manually and with a spatula. The water-swelling polyurethane resin Magistar was used for waterproofing the crown of the tunnel.

The Magistar system consists of a polyurethane resin and an accelerator for faster setting times. Through the right dosage, it is possible to adjust the mix reaction times. Once injected, Magistar swells when in contact with water to seal and consolidate the structure. 

The consolidation of the tunnel intrados 

The substrate preparation

The concrete lining at the tunnel intrados was irreversibly damaged by the very high temperature caused by the fire. According to the project design, the damaged layer was completely removed by scarifying approx. 10 cm of the surface layer.

  • Castello tunnel
    6 draco
    6. Grouting packer installation
  • Castello tunnel
    7 draco
    7. Positioning and fixing of the reinforcement mesh
The intrados lining with sprayed concrete

After cleaning, the reinforcement mesh was installed and anchored to the intrados of the arch by means of L-shaped anchors that were secured using Armofix MTL, a two-component epoxy resin-based adhesive made of selected aggregates and thixotropic agents which ensures high adhesion to all building materials and can be used for bonding and structural reinforcement.

Next, a layer of thixotropic Epox Ripresa was sprayed/applied by brush onto the mesh to boost adhesion of the mortar to the mesh. After applying the adhesive on the mesh, the lining of the tunnel intrados was made by spraying shotcrete mixed with Dranite AF 890, a liquid alkali-free setting accelerator for concrete and shotcrete, to form a thickness of about 10 cm.

By using an accelerating admixture, setting is faster, waste is minimised, and high mechanical properties can be obtained quickly.

  • Armofix MTL
    8 draco
    8. Detail of the L-shaped anchors fixed with resin Armofix MTL
  • shotcrete
    9 draco
    9. Laying of the Epox Ripresa layer

The portal structural consolidation (South entrance) 

Stitching of the through-wall crack

The existing crack was first filled and then stitched throughout its length. The surface around the crack was scarified creating a 1 m-wide and 10 cm deep area. A 10×10 cm electro-welded mesh was positioned in this area and fixed by means of steel fixing pins that were grouted using the two-component epoxy resin Armofix MTL.

The holes were arranged in a quincunx pattern, with a vertical spacing of 30 cm and inclined horizontally by 45° in order to intersect the two portions of concrete to be joined. Then the volume was restored and filled with a one-component fibre-reinforced thixotropic cement-based mortar.

Nailing of the portal

Lastly, the whole surface was nailed to anchor the portal by means of grouted steel bars with a diameter of 28 mm. The 5 m deep holes were drilled in a quincunx pattern with 1 m spacing.

  • Castello tunnel
    10 draco
    10. Intrados lining with sprayed concrete (shotcrete)
  • Castello tunnel
    11 draco
    11. Work in tunnel

Technical data

  • Client: Autostrade per l’Italia SpA
  • Construction Company: Pavimental SpA
  • Site Manager: Engineer C. Mangani
  • Supplier of special materials: Draco SpA

   Per la versione in Italiano: https://www.stradeeautostrade.it/gallerie-e-tunnelling/il-progetto-di-intervento-alla-galleria-castello/