Tunnels and Underground Cities: Engineering and Innovation meet Archaeology,Architecture and Art – Peila, Viggiani & Celestino (Eds)

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Fiber reinforced concrete segmental lining for CataniaMetro Tunnel

N. BonaCMC, Ravenna, Italy

A. MedaTunnelling Engineering Research Centre, University of Rome “Tor Vergata”, Rome, Italy

ABSTRACT: The use of Fiber Reinforced Concrete segments was proposed by CMC forthe Stesicoro – Airport part of Catania Metro Tunnel. The tunnel has an internal diameter of9.80 m with a lining thickness of 320 mm. The proposed solution forecast a light traditionalsteel cage, mainly along the segment perimeter, and the use of 40 kg/m3 of 4D steel fiber. Aprocess for obtaining the authorization of the Italian Authorities of the use of FiberReinforced Concrete was followed, according to the Italian Regulations. CMC obtained thefirst authorization issued in Italy for the use of Fiber Reinforce Concrete in new constructions.In order to evidence the effectiveness of the proposed solution, full scale tests were performedat the TERC (Tunnelling Engineering Research Centre) of the University of Rome “Tor Ver-gata”. Furthermore, a quality control process was defined in order to ensure the segment per-formances during the production.

1 INTRODUCTION

In the last few years the adoption of fiber reinforced concrete (FRC) in precast tunnel seg-ments, has encountered a great interest, as witnessed by theoretical and experimental studies(Plizzari and Tiberti, 2008; Caratelli et al., 2011; Liao et al., 2015), and actual applications(Kasper et al. 2008, De La Fuente et al., 2012, Caratelli et al., 2012).The use of Fiber Reinforced Concrete (FRC) in precast segments for tunnel lining is grow-

ing in the last years and this is becoming one of the principal applications of this material(Figure 1). Typically, two solutions are proposed: a hybrid solution, where fiber can partiallysubstitute the steel cage, and a FRC only solution, where the ordinary reinforcement is totallysubstituted by the fiber reinforcement.The main advantages linked to the use of FRC in tunnel segments are related not only to

the cost, but also to the possibility of enhancing structural and durability performances.After the publication of a series of National Codes, the publication of key documents as fib

Model Code 2010 (2013), certainly boosted the use of FRC application in tunnels. Alreadyseveral tunnels have been designed adopting Model Code 2010 as references document. Fur-thermore, a specific document for precast tunnel segments in fibre-reinforced concrete wasrecently issued (fib Bulletin 83, 2017).Since the use of FRC in segmental lining tunnels is an application that can be nowadays

considered common, CMC proposed this technology for Metro Catania tunnel. According tothe Italian Codes it was necessary to authorization of the Italian Authorities of the use ofFiber Reinforced Concrete.With this project, CMC obtained the first authorization issued in Italy for the use of Fiber

Reinforce Concrete in new constructions.

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2 CATANIA METRO: STESICORO-AEROPORTO LINE

Stesicoro- Aeroporto line is part of Metro Catania project. The line is under construction andit will connect Catania Airport with the part of the line already in service. CMC was in chargefor the construction of 2177 m of the line between the station of Stesicoro and Palermo.

A single tunnel is forecast for the line, with an internal diameter of 9.80 m with a liningthickness of 320 mm (Figure 3). The tunnel will be excavated with a TBM-EPB for a totallength of 2315 m (since some provisional parts are present).The precast segmental lining is characterized by 6 segments plus 1 key segment (6+1)

configuration.

Figure 1. FRC tunnel application in the recent years (from fib Bulletin 83).

Figure 2. Catania Metro.

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3 FIBER REINFORCED CONCRETE SOLUTION

The design of the FRC segments was made adopting fib Model Code 2010 are reference docu-ment. It was decided to adopt an hybrid solution, with fiber reinforcement coupled with alight perimeter reinforcement (Figure 4).The FRC performance was defined by classified the material as 4c according to fib Model

Code 2010. As a consequence, the residual characteristic tensile strength were fR1k > 4.0 MPaand fR3k > 3.6 MPa measured with EN 14651.

Figure 3. Catania Metro: tunnel lining.

Figure 4. Catania Metro: FRC hybrid solution segment.

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4 THE AUTHORIZATION PROCESS

In order to obtain the authorization for using the Fiber Reinforced Concrete solution, it wasrequired by the Italian authorities to perform and initial characterization of the material withEN 14651 bending tests on specimens and a full-scale bending test in order to verify the struc-tural behavior.The characterization according to EN 14651 is summarized in Table 1. 12 specimens were

tested for defining the characteristic value according to Eurocode 0, considering an unknowncoefficient of variation. These results were obtained by adding 40 kg/m3 of Bekaert 4D steelfiber to theThe bending tests were performed with the loading set-up illustrated in Figure 5, by adopt-

ing a 4000kN hydraulic jacket.The segments were placed on cylindrical support with a span of 3000 mm and the load,

applied at the midspan, was transversally distributed be adopting a steel beam as shown inFigure 5. The measure devices, consisting in four potentiometer wires transducers and twoLVDTs, are shown in Figure 6.Figure 7 shows the results of the bending test in terms of load versus displacement diagram.Figure 8 shows the crack pattern at different loading steps. Figure 9 shows the opening of

the principal crack.In order to compare the experimental behavior with a traditional reinforced concrete seg-

ment, it was request to CMC to test a segment produced for another part of the line where theFRC was not forecast (Nesima-Misterbianco line, already excavated). The segment has thesame geometry of the FRC segment but it is reinforced with only a steel cage (Figure 10) wasdesigned for higher load level. For this reason in the comparison of Figure 11, the ultimatedesign load for the two cases is reported.The comparison between the two segments evidenced an interesting result: referring to a

crack opening value of 0.2 mm, this limit was reached at a load level of 188 kN for the FRCsegment and at a load level of 150 kN for the traditional reinforced concrete segment. Thecrack opening was significantly smaller in the FRC segment respect to the traditional RC one.After the test campaign CMC was authorized by the Italian Authorities to adopt FRC in

the project.

Table 1. Material characterization.

fl fR1 fR3

4.6 5.2 6.2

5.5 7.6 7.8

6.3 6.5 6.4

6.5 7.9 7.4

5.9 7.8 9.3

5.0 5.8 8.2

6.1 6.7 8.3

5.3 5.2 6.5

6.0 6.5 8.6

5.1 5.6 6.7

5.7 7.5 8.2

5.7 6.9 8.0

Average 5.6 6.6 7.6

Standard dev 0.56 0.98 0.99

Coef. var. 0.10 0.15 0.13

Kn 1.87 1.87 1.87

flk fR1k fR3k

4.53 4.67 5.70

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Figure 5. Bending test set-up.

Figure 6. Bending test instrumentation.

Figure 7. Bending test results.

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Figure 8. Bending test crack pattern.

Figure 9. crack opening.

Figure 10. Traditional reinforcement in Nesima-Misterbianco segment.

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This authorization was the first one issued in Italy for the use of FRC

5 CONCLUSIONS

CMC proposed the use of FRC segment for the Catania Metro Stesicoro-Aeroporto line. Thetunnel lining was designed according to fib Model Code 2010.In order to obtain the authorization, according to Italian Code a process was followed, by

performing full scale tests.The tests highlighted the good performances of the FRC solution and the authorization was

issued.

REFERENCES

Caratelli, A., Meda, A., Rinaldi, Z., Romualdi, P. 2011. Structural behaviour of precast tunnel segments

in fiber reinforced concrete. Tunnelling and Underground Space Technology 26: 284–291.

Caratelli, A., Meda, A., Rinaldi, Z. 2012. Design according to MC2010 of a fibre-reinforced concrete

tunnel in Monte Lirio, Panama. Structural Concrete 13(3): 166–173.

Cosenza, E., Manfredi, G., and Realfonzo, R. 1997. Behavior and Modeling of Bond of FRP Rebars to

Concrete. Journal of Composites for Construction 1(2): 40–51.

De la Fuente, A, Pujadas, P, Blanco, A, Aguado, A. 2012 Experiences in Barcelona with the use of fibres

in segmental linings. Tunnelling and Underground Space Technology 27(1): 60–71.

Di Carlo, F., Meda, A., Rinaldi, Z. 2016. Design procedure of precast fiber reinforced segments for

tunnel lining construction. Structural Concrete 17(5): 747–759.

EN 14651. 2005. Test method for metallic fibre concrete – Measuring the flexural tensile strength.

fib Bulletin No. 83. 2017. Precast tunnel segment in fiber-reinforced concrete.

fib Model Code for Concrete Structures 2010. 2013. Ernst & Sohn.

Liao, L., De La Fuente A, Cavalaro S, Aguado A. 2015. Design of FRC tunnel segments considering the

ductility requirements of the Model Code 2010. Tunnelling and Underground Space Technology 47:

200–210.

Meda, A., Rinaldi, Z., Caratelli, A., Cignitti, F. 2016. Experimental investigation on precast tunnel seg-

ments under TBM thrust action. Engineering Structures 119(15): 174–185.

Plizzari, GA, Tiberti, G. 2008. Steel fibers as reinforcement for precast tunnel segments. Tunnelling and

Underground Space Technology 21: 3–4.

Figure 11. Comparison between traditional and FRC solution.

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