RIEDMÜLLER ET AL.: PREDICTION OF SUPPORT FOR THE PRELIMINARY DESIGN OF THE ANILIO TUNNEL (EGNATIA MOTORWAY)

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Preliminary Design of the AnilioTunnel (Egnatia Motorway)By Gunter Riedmüller, Wulf Schubert, Arnold Steidland Wolfgang Holzleitner

Ingenieurgeologische Untersuchungenund Prognose der Stützmittel fürdie Vorplanung des Anilio-Tunnels

Für den Anilio-Tunnel, einem Schlüssel-projekt der Egnatia-Autobahn in NW Grie-chenland wurden ergänzende Erkundun-gen und Analysen durchgeführt. Die Tun-neltrasse befindet sich in dem komplex auf-gebauten Falten- und Deckenbau der Pin-dosdecke. Die Erkundungen umfassten geo-logische Geländekartierungen mit struk-turgeologischen Analysen als besonderenSchwerpunkt, die geotechnische Definitionvon Gebirgstypen und geophysikalische Ex-plorationen. Die Ergebnisse der Geländear-beit, kombiniert mit den Ergebnissen vonLaboranalysen an Gesteinsproben, ermög-lichten die Berechnung von Radialverschie-bungen und der Tiefe plastischer Zonen.Beide Parameter bilden einen wesentlichenInput für die Erfassung von Stützmittel-klassen.

Supplementary investigations and analyseswere performed for the preliminary designof the Anilio tunnel which is one of the keyprojects of the Egnatia Motorway in NWGreece. The tunnel alignment is located inthe complex fold-and thrust belt of the Pin-dos nappe. The investigations included geo-logical field mapping with special emphasison structural geological analyses, the geo-technical definition of rock mass types andgeophysical surveys. The results from thesefield studies combined with the results fromlaboratory analyses of rock samples wereused to calculate radial displacements andthe depths of broken zones, both parametersbeing an essential input for the assessmentof support classes.

The Egnatia Motorway is one of Europe’smost spectacular traffic projects. The align-ment follows the Ancient Roman Via Egnatiathrough the mountainous area of northernGreece. After completion of the Egnatia Motor-way a high capacity road will exist between Igou-menitsa at the Adriatic Sea and Thessaloniki atthe Aegean Sea. The successive natural andman-made environments along the alignmentare exceptionally diverse, both through the Pin-

dos mountains of Epiros and Western Macedo-nia, and the plains of Central Macedonia andThrace.

One of the key sections of the motorway is theAnilio Tunnel which will bypass the picturesquesmall town Metsovo located in the Pindos moun-tains (Figure 1). Initially the bypass was plannedas an open section downhill of the village Aniliosituated at the north-westerly exposed left slopeof the Metsovo River. Due to active deep seated

Fig. 1 Location map.Bild 1 Lage des Projektgebiets.

Fig. 2 Project area showing the unstable slope at Anilio village.Bild 2 Projektgebiet mit dem instabilen Hang beim Ort Anilio.

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slope creep and sliding (Figure 2) a tunnel alter-native which underpasses the mass movementswas designed. The west portal of this tunnel willbe connected with a viaduct which will bridgethe Metsovo River. The east portal is located in agentle slope with local superficial creeping andsliding. After successfully coping with geotechni-cal difficulties during construction of the pre-cutthe tunnel excavation has recently started at thisportal (Figure 3). The twin tube tunnel isplanned to have a total length of 2 135 m, with amaximum overburden in the range of 240 m.

For the preliminary design of this tunnel ad-ditional engineering geological site investiga-tions, mechanical laboratory testing and geo-mechanical analyses were performed. The ob-

jective of these geotechnical studies was the as-sessment of the geological architecture, the de-termination of geotechnical relevant key pa-rameters as basis for the rock mass character-isation and the prediction of displacementmagnitude and support class distribution alongthe tunnel route.

Regional geology

The tunnel alignment is located in the Pindosflysch nappe which consists of a flysch sequenceof the early Tertiary period. The sediment series,reaching a thickness of several thousand meters,include an alternation of sandstone and siltstonewith intercalations of claystone. The sequence iscomposed of three major sections: a wildflyschunit displaying large and irregularly sortedblocks resulting from subaquatic sliding formsthe top, underlain by a thick sequence of grey-wacke intercalations in the central part. Grey tored marls, the so called “Red Flysch” form thebase. (1).

The Pindos flysch nappe is part of a fold-and-thrust belt which thrusted over the miogeoclinalsediments of the West Hellenic nappe in the westand was in turn overthrusted by melange ter-ranes associated with ophiolithe and olisto-strome complexes in the east. The N-S trendingwest vergent fold-and-thrust belt system dis-plays a rough symmetry of typical external thin-skinned fold and thrust nappes. The age of over-thrust is early to middle Miocene. Younger high-angle faults are present throughout the belt.

Fig. 3 East portal ofthe Anilio Tunnel.Bild 3 Ostportal desAnilio-Tunnels.

Fig. 4 Geologicalmap of the tunnelalignment.Bild 4 GeologischeKarte der Tunnel-trasse.

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Alignment geology

The complex geological environment of the tun-nel alignment required a structural geologicalanalysis by means of outcrop studies and map-ping in scale 1 : 5 000 (Figure 4). The results re-vealed extreme heterogeneous rock mass condi-tions. Thick competent layers of sandstone withsiltstone interlayers alternate with the “RedFlysch” sequence. This thinly to medium beddedsequence with interlayers of sandstone and silt-stone is intensely folded and sheared. Dishar-monic kink and chevron folds developed whichdie out at faults (Figures 5 and 6). Of great geo-technical importance is the development ofblock-in-matrix-rock (2, 3). The bimrock unitsare limited to the “Red Flysch” sequence. Thisheterogeneous mixture of competent sandstoneblocks embedded in a weak matrix of fine-grained, mainly clayey gouge, was found withconsiderable thickness along thrust faults (Fig-ure 7).

The thrust faults, which intersect the tunnelaxis with obtuse angles, form a number of indi-vidual listric sheets, all dipping moderately to-wards east. It is assumed that, at depth, thethrust faults terminate at branch lines along abasal floor thrust (Figure 8).

The thrust sheets are segmented by generallyNW- to WNW-trending tear faults. The lateraltermination of fold hings against these high an-gle strike-slip faults was observed in the vicinityof the west portal. It becomes obvious by thisfield observation that the tear faults accommo-date differential displacements along the thrusts(4).

The geological model as revealed by detailedgeological field studies was confirmed by explor-atory drilling and geophysical surveys at depth.The authors strongly emphasise that in particu-lar complex geological environments, such as Al-pine fold-and-thrust belts, require careful geo-logical field mapping prior to any subsurface in-vestigations (5).

Definition of rock mass types

Based on the results of site investigations 6 rockmass types and 1 soil type were defined. The def-inition of rock mass types (RMT) takes into ac-count the physical condition of the rock mass fol-lowing the soil and rock description suggested byISRM (6).➮ RMT 1: Medium to fine-grained, brownish-

grey, mainly thickly to medium bedded sand-stone, occasionally with interlayers of silt-stone (mudstone). Strength of intact rockranges from medium to very strong (UCS 37 to116 MPa). Discontinuities are very widely tomoderately spaced (200 to 6 000 mm). Thepersistence of joints range from very low tomedium (< 1 to 10 m). Joint surfaces aremainly rough and plain (JRC 8 to 14). Bedding

planes are rather smooth to rough and planar(JRC 4 to 8). Discontinuity surfaces are partlystained. Thin infillings and coatings of residu-al soil, silt and clay may occasionally occur.The rock mass is generally fresh to slightlyweathered.

➮ RMT 2: The same as RMT 1 but heavily frac-tured and locally strongly weathered. Thestrength of intact rock is de-creased.

➮ RMT 3: Sequence of grey tobrownish-grey or red siltstone(mudstone) with occasional in-tercalations of sandstone. Bed-ding plane spacing ranges fromthinly laminated (< 6 mm) tothinly bedded (60 to 200 mm).Bedding surfaces are mainlysmooth and planar (JRC 2 to 6)with occasional clayey coatings.Joints have a very low persist-ence (< 1 m). Intact rock strengthvaries considerably (1 to 77 MPa).

➮ RMT 4: Brownish-grey or redsiltstone - sandstone alternation.The characteristics of siltstone

Fig. 5 Typical disharmonic chevron folds developed in the “Red Flysch” sequence.Bild 5 Typische disharmonische Chevron Falten in der „Red Flysch“-Folge.

Fig. 6 Disharmonic chevron folds in sandstone of the “Red Flysch” sequence.The folds die out at a thrust fault.Bild 6 Disharmonische Faltung im Sandstein der„Red Flysch“-Folge. Die Faltenenden an einer Aufschiebung.

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are similar to RMT 3. Sandstone interlayersare thinly bedded and more persistent.

➮ RMT 5: Tectonic block-in matrix rock consist-ing of mainly red siltstone - sandstone alter-nations (“Red Flysch”). The rocks are intense-ly sheared and folded. Competent blocks ofsandstone and siltstone varying in size andshape occur in silty to clayey gouge matrix.Main characteristics are a heterogeneous,chaotic structure and very low strength prop-erties of the matrix, larger blocks may beheavily fractured.

➮ RMT 6: Rock mass dominated by weak, clayeyfault gouge, occasionally fault breccia andheavily fractured rocks, characterized by ex-tremely low strength properties.

➮ RMT S (Engineering soil): The engineering soilincludes non-compacted Quaternary sedi-ments, slope debris and residual soil.

Definition of support classes

The definition of support classes which includessupport quantities and round length, is adjustedto the anticipated behaviour of the rock massduring excavation. Rock mass types (physicalcondition of the rock mass) and rock mass be-haviour correspond largely but not necessarily.

All descriptions below are based on the as-sumption of a sequential tunnel excavation sub-divided into a top and bench heading.

Support class AThis support class is used for stable conditions.The stable rock mass allows round lengths of 2 to3 m. Only local small discontinuity controlledfailure is expected.

10 to 15 cm of wire mesh reinforced shotcretein the top heading and 5 cm shotcrete withoutreinforcement in the bench are provided. Spotbolting with Swellex bolts in the crown preventsrapid loosening and detachment of single blocks.

Support class BThis support Class is used for blocky rock masswith overbreak potential. Rock mass failures areclearly controlled by discontinuities.

The round length is kept at 2 to 3 m. The sup-port as selected for support class A is increasedby one set of lattice girder per round, 10 cm shot-crete lining in the bench and grouted bolts in thetop heading will prevent the development ofoverbreak.

Support class CThis support class is designed for weathered,loosened rock with low overburden (portal are-as).

Fig. 8 Geologicallongitudinal sectionwith radial displace-ments and distributionof support classes.Bild 8 GeologischerLängenschnitt mitRadialverschiebungenund der Verteilung vonStützmittelklassen.

Fig. 7 Bimrockdeveloped along athrust fault in “RedFlysch”. Blocks of

sandstone varying insize and shape are

surrounded by clayeygouge.

Bild 7 Bimrock-Bildung entlang einer

Aufschiebung im „RedFlysch“. Unterschied-

lich große und geform-te Blöcke werden von

tonigen Kataklasitenumflossen.

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FELSBAU 20 (2002) NO. 4

Due to the deficiency of side pressure theround length varies between 1.2 to 1.5 m. 20 cmof reinforced shotcrete, one set of lattice girdersper round, and grouted bolts at the sidewallswith a length of 6 m in the top heading and 4 m inthe bench are provided. Forepoling should beapplied to prevent overbreak. Bench roundlength and shotcrete thickness correspond withthe top heading. Each second lattice girder isextended down to the invert. Face protection bya thin layer of shotcrete is required.

Support class DThis support type should be applied for RMT 3with low overburden and adverse influence ofground water.

The round length does not exceed 1.5 m. Thesupport is based on support class C, but bolts areadditionally applied in the crown. Protection ofthe top heading invert will be required by pres-ence of groundwater. An invert protection (geo-textile, drainage and backfill) is provided undersuch circumstances.

Support class EThis type of support is provided for rock masstypes with unfavourable orientation of beddingplanes (steeply dipping, and striking subparallelto the tunnel axis).

To prevent large overbreak, possibly develop-ing into chimney failures, and to prevent shear-ing and buckling along bedding a dense rockboltpattern is designed. Bolt orientation shall be ad-

justed to the discontinuity orientation to achievemaximum effect. Due to the steeply dipping bed-ding, special care has to be taken for bolting inthe top heading to avoid major problems duringbench excavation. Round length in the top head-ing is 1.5 m. The round length in the bench is3 m.

Support class FThis support type is used in sections, wherestresses considerably exceed the rock massstrength, but magnitude of displacements stillallows a stiff type of support with a lining thick-ness of 25 cm. A temporary top heading invert,forepoling, face sealing, and occasionally facebolting is provided. An invert arch is mandatoryfor this type of rock mass. The round lengthamounts to 1 to 1.2 m in the top heading andsomewhat longer in the bench.

Support class GClass G is used in fault zones, where displace-ments exceed the deformability of the conven-tional lining. The type of support is similar tosupport class F, but yielding elements (LSC) willprovide a flexibility of the lining (7). Rock boltshave a length of 6 m, in general. Face support,temporary invert in the top heading and anarched, deep invert is required. Round lengthamounts to 1 m for the top heading and to 2 m atthe bench.

Support class G+This support type is provided for extremely poorrock conditions under high stress. The type isbased on type support class G, but shotcretethickness is increased to 30 cm, yielding ele-ments are adjusted to the thicker lining, and therock bolt density is increased by 30 to 40 % com-pared to type support class G.

Prediction of displacementmagnitudes and support classdistribution

The prediction of support class distributions wasprimarily based on the assessment of displace-ment magnitudes and depth of broken zones.

For a first rough appraisal of the depth of thebroken zone, the magnitude of displacementsand the influence of support an analytical ap-proach suggested by Feder (8) was used. Modify-ing Feder’s procedure systematic nonnumericcalculations were performed stepwise in 20 msections along the tunnel axis. The efficiency andsuitability of the selected support was addition-ally confirmed by numerical calculations (UDEC3.0) at selected cross sections.

The procedure which finally resulted in theprediction of support class distributions alongthe tunnel included as essential input the geolog-ical alignment architecture, the distribution ofrock mass types and relevant mechanical pa-

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rameters from laboratory tests and geophysicalsurveys (UCS, ϕ, c, Estat, Edyn). Further inputswere influencing factors, such as primary stress(calculated by the height of overburden, using2.7 t/m3 as specific weight, and simplified withko = 1), the orientation of discontinuities, andgroundwater.

Figure 8 displays the result of this procedurewhich includes the distribution of support class-es along the alignment (shaded), as well as theexpected displacements in each section (blacksingle columns). It can be clearly seen that faultzones, in particular tunnel sections in the tecton-ic melange of siltstone – sandstone alternations(“Red Flysch”) with increased overburden have ahigh potential for displacement and develop-ment of deep reaching broken zones. With thechosen support expected displacements remainwithin tolerable limits. At the transition from“Red Flysch” to the competent sandstone (ap-proximately Station 12 750 m) displacementsexceed 20 cm. In this crucial section with highoverburden a thrust zone is predicted.

Concluding Remarks

This article presented an investigation approachwhich can be used for the preliminary design oftunnels in a complex geological environment,such as usually found worldwide in Alpine fold-and-thrust belts. The authors recommend to pututmost care on detailed geological field studies,in particular on a comprehensive structural geo-logical analysis which should exceed the imme-diate vicinity of the tunnel alignment.

Of great importance is the selection of geo-technical relevant key parameters as input forthe definition of rock mass types and mechanicalcalculations (9). It is the authors´ experience tobegin the analytical procedure stepwise with rel-atively simple calculations and to check the re-sults by numerical calculations at selected sec-tions (10). Significant data for the appropriateassessment of support classes are radial dis-placements and the depth of the broken zone.However, due to various simplifications in inputparameters and boundary conditions displace-

ments and depths of broken zones calculated bythe analytical procedure can not be very accu-rate. Nevertheless, the calculated results, com-bined with experiences from previous projects,can be used for the preliminary design of a tech-nically sufficient and economical support.

References1. Jacobshagen, V.: Geologie von Griechenland. Berlin,Stuttgart: Bornträger, 1986.2. Medley, E.W.: Orderly Characterization of the chaoticFranciscan Melanges. In: Felsbau 19 (2001), No. 4, p. 20-33.3. Button, E.A. ; Schubert, W. ; Riedmüller, G.: Shallow tun-nelling in a tectonic melange – rock mass characterizationand data interpretation. NARMS-TAC 2002, Hammah et al.(eds), University of Toronto, 2002, p. 1125-1132.4. Twiss, R.J. ; Moores, E.M.: Structural Geology. New York:W.H. Freeman 1992.5 Riedmüller, G.: The importance of geological field investi-gation for the design of tunnels: In: Felsbau 16 (1998), No. 5,p. 284-288.6. ISRM (Committee on Field Tests, Doc. No. 4, 1977): Sug-gested methods for the quantitative description of discontinu-ities in rock masses, In: Int. J. Rock Mech. Min. Sci. & Geo-mech. Abstr. 15 (1978), p. 319-368.7. Schubert, W. ; Moritz, B.: Controllable ductile support sys-tem for tunnels in squeezing rock. In: Felsbau 16 (1998),No. 4, p. 224-227.8. Feder, G.: Versuchsergebnisse und analytische Ansätzezum Scherbruchmechanismus im Bereich tiefliegender Tun-nel. In: Rock Mechanics, Suppl. 6 (1978), p. 71-102.9. Riedmüller, G. ; Schubert, W.: Project and rock mass spe-cific investigation for tunnels. Särkkä & Eloranta (eds): RockMechanics – a Challenge for Society. p. 369-376. Lisse Es-poo, Finland: Swets & Zeitlinger, 2001.10. Schubert, W. ; Goricki, A. ; Button, E.A. ; Riedmüller, G. ;Pölsler, P. ; Steindorfer, A.F. ; Vanek, R.: Consistent excava-tion and support determination for the design and construc-tion of tunnels. In: Felsbau 19 (2001), No. 5, p. 85-92.

AuthorsUniv.-Professor Dr.phil. Gunter Riedmüller, Univ.-ProfessorDr. Wulf Schubert, Mag. Arnold Steidl, 3G – Gruppe Geo-technik Graz, Elisabethstrasse 22/II, A-8010 Graz, Austria,E-Mail office@3-g.at, and Dipl.-Ing. Wolfgang Holzleitner,Bernard + Partner Consulting Engineers, ZT Ges.m.b.h.,Bahnhofstr. 19, A-6060 Hall in Tirol, Austria, E-Mail tunnel@bernard-partner.at

AcknowledgementThe authors wish to express appreciation to Professors EvertHoek and Paul Marinos, as well as Nikolaos Kazilis of Egna-tia Odos A.E. for discussions on site and inspirations. Wealso want to thank Ilias Sotiropoulos for getting us involvedinto this interesting and challenging project.