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Underground Space the 4th Dimension of Metropolises Bartk, Hrdina, Romancov & Zlmal (eds) 2007 Taylor & Francis Group, London, ISBN 978-0-415-40807-3

Geomechanical studies for a road tunnel in volcanic formations

A.T. Menezes, F.M. Varela & L. Ribeiro e SousaUniversity of Porto, Porto, Portugal

F. MouraUniversity of Minho, Guimares, Portugal

ABSTRACT: The extremely mountainous and the heterogeneous volcanic rock formations of the MadeiraIsland led to the construction of an important road network where the tunnels are dominants, representingabout 14% of the total network. In this paper the analysis of a road tunnel between Canio and Camacha is

presented, along with the description of the construction and of the geotechnical information. The evaluation ofthe geomechanical rock mass properties using empiric systems and 2D and 3D numerical analysis of sectionsof a tunnel are presented. Finally an empirical system that was developed for tunnels in volcanic rocks commonat Madeira Island is also presented.

1 ROAD TUNNELS AT MADEIRA ISLAND

The road tunnels of new transport system of MadeiraIsland were strongly affectedby the heterogeneous andcomplex volcanic formations, by the topography andby the land occupation. All these factors originate thedesign of a large spectrum of innovative structuralsolutions that permit to achieve economic solutionsmore adequate to the topographic and geologicalconditions.

The new road transport network, with high radiicurves and morereduced longitudinal inclinations per-mitted easy and comfortable accesses to the wholeisland. The regional road system length is about546 km, with about 78 km in tunnels. In the new high-ways the relation is about 43% in tunnels, in totalof 173 km. More important works are still planned,

mainly in the Northern part of the island, also with animportant of these being tunnels (Moura and Sousa2006).

The geology of Madeira Island comprise five vol-canic complexes (Figure 1): 1 mio-pliocenic vol-canic complex of Curral das Freiras, Serra de gua,Vale de So Vicente and Vale da Boaventura, in westpart of the island and Ruivo e Areeiro mountains,So Roque, Porto da Cruz, Machico and Ponta deSo Loureno; 2 pos-miocenic volcanic complexat Ribeira da Janela, Porto Moniz, Ponta do Pargo,Ribeira Brava and Cmara de Lobos, in the west

part, and Funchal, Camacha, Santa Cruz and Santana,including tuffs at Arco de So Jorge; 3 pos-miocenic volcanic complex of Pal da Serra, Achada

Figure 1. Identification of the geological-geotechnical for-mations at Madeira Island.

da Pinta and Lombada das Vacas, at west part, and

Lombada do Meio, Cabeos de Faj dos Vinhticosand Terreiro da Luta, in the east part of the island;4 Superior basaltic complex of Pal da Serra, Chodos Balces, Poiso andAchada doTeixeira; 5Mod-ern basaltic lava of Porto Moniz and the valleys of SoVicente and Seixal.

The transversal section of the road tunnels atMadeira Island Region have a horse-shoe (semi-circulat arch) cross section with a span of 9.0m,for tunnels with one directional of traffic and 9.6 mfor tunnels with two directions of traffic. Both typesof tunnels consist of two lanes with a width of 3.5 m.

In some older tunnels a semi-elliptic arch was adopted(Joo Gomes andJardim Botnico tunnels). Some tun-nels may have up to three (Pestana Jnior tunnel) or

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Figure 2. One traffic directional tunnel with two lanes.

Figure 3. One traffic directional tunnel with two lanes.

four lanes (Santa Cruz West and East tunnels). Herethe width is 18.5 m, in order to allow 2 lanes in eachdirection, separated by a central separator.

Figures 2 to 4 presents examples of geometriccharacteristics of road tunnels constructed at MadeiraIsland.

2 CANIO-CAMACHA TUNNELS

InordertoestablisharoadliaisonbetweenCancelaandNogueira located in the townsof Canio and Camacha,respectively, important viaducts and tunnels were con-structed in a mountainous region of Madeira in anextension of about 3.9 km. Of these an extension of2.44 km (63% of the total) consisted of four tunnels.They have two directional of traffic with a lane in eachdirection (until km 0+725 including Tunnel 1) andwithtwolanesintheNorthdirection(sincekm0+725)for heavy traffic (trucks).

This paper is focus in Tunnel 2. Two sections arebeing considered, A (km 1+167) and B (km 1+256).Section A crosses a zone of disaggregated to moderate

Figure 4. Two traffic directions tunnel with four lanes.

Figure 5. Construction sequence for section A.

compacted breccias. Section B corresponds to a zoneof disaggregated and compact breccias, and compactbasalts.

The design of supports adopted for the differenttypes of rock formations were based on empiricalmethodologies (Vis 2001). In this tunnel supportsused on both sections A and B were the following:bolts length of 4 m, 20 mm in diameter and a capac-ity of 177 kN, 1.5 m spacing in the ceiling and 2.0 min the walls for section A and 1.0 m for section B;shotcrete10 cm in thickness for section A and 5 cmfor section B; steel linings only for section A, a pro-

fileHEB160 spacing of0.8in upper partofthe section.As usually done at Madeira Island a final concretesupport was adopted with a thickness of 30 cm wasadopted.

The construction process adopted is the SequentialExcavation Method (SEM). Due to the strong hetero-geneity of the volcanic formations the constructionwas versatile in order to consider theadaptability to thedifferent geotechnical conditions. Section A of Tun-nel 2 has an overburden of about 3.9 m, composedby rock material of weak geomechanical quality. Theconstruction sequence is illustrated in Figure 5. Sec-

tion B has an overburden of 26 m composed of basaltof good geomechanical. The construction sequence ispresented in Figure 6.

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Figure 6. Construction sequence for section B.

Table 1. Results of uniaxial tests.

SamplesE c

Borehole Depth(m) (GPa) (MPa)

S2 19.820.25 117.5S5 8.558.85 1.55S12 12.612.97 14.7 63.8S13 31.431.7 316.0S14 9.29.55 37.0 63.3S38 20.320.95 2.2

3 EVALUATION OF THE GEOMECHANICALPARAMETERS

Tunnel 2 is located in the volcanic complex 2, thatis composed by basalts and by piroclastic materialswith variable dimensions like tuffs, breccias and sco-ria. The geotechnical survey of the tunnel consistedof boreholes and laboratory tests. The deformabilityand strength properties were estimated based on lab-oratory tests results. Table 1 shows some results ofthe Young modulus (E) and uniaxial strength (c).Theresults from the survey show highly complex hetero-geneous formations from complex 2 with differenttypes of formations apart the surface soil formationswith about 3 m thickness:

Compact basalt predominant lithology witha weathering degree between W3 to W1-2; RQDbetween 60100; E= [1746]GPa and c = [35100]MPa.

Volcanic breccias with the basalts is also an impor-tant lithology with a matrix highly variable, beingmore or less compact. The weathering degree variesbetween W4 to W3; RQD is in average 50, being nullin the disaggregated breccias; E= [0.133]GPa andc = [135]MPa.

Volcanic tuffs the less important lithology appear-ing in the upper part of the rock mass. The weathering

degree varies between W4-5 to W3; RQD is in aver-age 60, with a wide spectrum; E= [0.15]GPa andc = [0.918]MPa.

Table 2. Geomechanical parameters.

Parameter Disaggregated Moderatebreccia compact breccia

Section A

(kN/m3) 25 25E (GPa) 1.5 3.6c (MPa) 10.3 10.3mb (HB crit.) 0.154 0.682s (HB crit.) 5.44 106 0.0002

Parameter Disaggregated Compact Compactbreccia breccia basalt

Section B

(kN/m3) 25 25 29E (GPa) 1.6 5.6 19.5c (MPa) 10.3 10.3 170mb (HB crit.) 0.154 0.605 1.572s (HB crit.) 5.44 106 0.0002 0.0023

The geomechanical parameters were determinedthrough the RMR empirical system. Relevant aver-age geomechanical parameter values are presentedin Table 2. Probabilistic approaches and a softwaredeveloped for underground construction designatedGEOPAT were used to obtain a probabilistic distri-bution and average values (Costa et al. 2002; Mirandaet al. 2005).

4 STRUCTURAL BEHAVIOR OFCANIO-CAMACHA TUNNEL

The structural analysis of Tunnel 2 was performedusing the software Phases2 from Rockscience for 2Danalysis and FLAC 3D from Itasca, for the 3D anal-ysis. The two referred sections A (portal section) andB.(inside the rock mass) were considered. The in situstateofstressadoptedconsideredaratioof0.8betweenin situ state horizontal and vertical. Section A analy-

sis required a 3D model using 93527 nodal points and2464 shell elements (Figures 7 and 8). For section Aand using 2D approaches Figures 9 and 10 reveals theinitial and final meshes.

The maximum settlement at the tunnel crown wasabout 5.8 mm and maximum convergences measuredwere equal to 10,0mm. Settlements at surface werealso evaluated in order to assess any possible damageon the buildings. The yielded zones were evaluated.They are mainly located at the disaggregated brecciathat exhibited low strength.

Some results of the 2D analysis of section A are

presented in Figures 11 and 12.As a result two situations for the reinforcement ofthe crown tunnel were analyzed. One considered the

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use of forepoling and other the use of bolts. The useof forepoling led clearly to the reducing of the yieldedzones of the rock mass.

Figure 7. Detail of the 3D mesh near the tunnel.

Figure 8. Detail of the 3D mesh near the tunnel.

Figure 9. Initial 2D mesh for section A.

Figure 10. Final 2D mesh for section A.

In the portal 3D analysis were performed consider-ing a 5 step excavation sequence following as proxy aspossible the construction procedure. Table 3 indicatesthe geomechanical properties adopted at FLAC 3D.

Figures 13 to 15 present some obtainedresults at thelast excavation stage. A comparison with 2D resultsshows that the displacements obtained with the 3D

Figure 11. Displacements in the last stage.

Figure 12. Yielded points at last stage.

Table 3. Geomechanical properties for FLAC 3D model.

K G c cFormation (Pa) (Pa) (Pa) () (Pa)

Disaggregated 1.03 6.15 9720 36.6 10.25breccia E+09 E+08 E+06

Median compact 2.39 1.43 7880 36.8 10.25breccia E+09 E+09 0 E+06

Figure 13. Vertical displacements in the last stage.

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model were higher. The maximum displacement is inthis case of about 1.7 cm, in the left side of the crown.The maximum stresses are registered in the vicinity ofthe excavation e mainly in the walls.

5 EMPRICAL SYSTEM FOR VOLCANICROCK FORMATIONS

An empiric system was developed specifically for vol-canic rock formations. It was adapted by the RMRsystem and by a classification developed at IPT, So

Figure 14. Principal stresses at final stage

Table 4. Application of the proposed classification for volcanic rocks.

Parameters Rock Mass classification and weights

P1 Uniaxial strength R1 R2 R3 R4 R5>120 MPa 60120 MPa 3060 MPa 1530 MPa

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Table 5. Parameters for rock weathering.

Parameter Description

A1 Sound or practically soundA2 Median weathered

A3 Highly or very highly weathered

Table 6. Parameters for joint frequency.

Parameter Description

F1 Joint spacing >1 mF2 Joint spacing 0.251 mF3 Joint spacing 0.10.25 mF4 Joint spacing 0.060.1 mF5 Joint spacing

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since only convergences were measured in a certaindistance of the front of excavation.

ACKNOWLEDGEMENTS

The authors are greatly indebted to Road RegionalDirection of the Autonomic Region of Madeira forauthorizing the publication of this paper. They alsowish to thank Mr Tiago Miranda from the Universityof Minho for his help in the 3D modeling.

REFERENCES

Costa, P.; Monteiro, A.; Oliveira, R.; Gaio, R.; Baio, C.;Sousa, L.R. 2002. Geotechnical analysis of the Canialtunnel, Madeira Island.ISRM Symposium EUROCK 2002

on Rock Engineering for Mountainous Regions, Funchal,Ed. D. Gama and R. Sousa, pp. 579588.

Miranda,T.; Correia, A.;Sousa, L.R.; Lima, C. 2004. Numer-ical modeling of a large underground powerhouse usinggeomechanical parameters obtained by artificial intelli-gence techniques. ISRM Int. Symposium on Contributionof Rock Mechanics to the New Century, Kyoto, Ed. Y.

Ohnishi & K. Aoki, pp. 579584.

Moura, F., Sousa, L.R. 2006. The road tunnels in Madeira.Methodologies of construction and safety. University ofMinho, Individual Project, Guimaraes, 14p.

Ojima, L.M. 1981. Methodology of rock mass classifica-tion applicable to tunnels (in Portuguese). LNEC thesis,Lisbon.

Vis 2001. Geological-geotechnical study Road highwayCanio-Camacha (Madeira).Vis, Consultoria, Estudos eProjectos de Engenharia, Lda.

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