Engineering Geology and the Environment, Marinos, Koukis, Tsiambaos & Stournaras (eds) - pp. 2639-2645 © 1997 Balkema, Rotterdam, ISBN 90 54 10 877 0 Adverse geotechnical conditions in road construction. Sections of the new Egnatia highway across Pindos mountain range (N. )

B. Christaras, N. Zouros, Th. Makedon, A. Dimitriou Lab. of Engineering Geology & Hydrogeology, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece.

ABSTRACT: The investigation of the geological and geomechanical factors that affect the construction of important traffic arteries such as the Egnatia Highway, is of utmost importance. The problems arising in the construction of Egnatia Highway are due to the complex geotectonic regime of the Pindos area, which generates various instability conditions. The present paper’s purpose is to specify the tectonic and geomechanical features that are responsible for the creation of these problems in the construction of Metsovo- Malakasi-Panagia part.

INTRODUCTION Highway in North-Western Greece is crossing Pindos mountain range and is considered to be one The Egnatia highway is the most significant of the most difficult parts for its construction. It traffic artery in Greece. It is also the main artery includes complex geological formations that have linking trade and commerce from Western and undergone multiple tectonic deformations. The rock Central Europe to the Middle East, as part of the mass, under these conditions, is highly anisotropic traffic network of the European Union. The Egnatia and in association with the morphology (high relief

Figure Σφάλµα! Άγνωστη παράµετρος αλλαγής.. Sketch showing the Egnatia highway section in Pindos mountain. The present investigation was performed in Metsovo - Malakasi - Panagia area.

Figure Σφάλµα! Άγνωστη παράµετρος αλλαγής.. Schematic geological sketch map showing the main tectonic features in the study area.1. Pindos flysch (Fo), 2. Ophiolites, 3. Deep sea sediments with basic volcanics and the tectonic formation, 4. Tectonic contact between ophiolites and flysch, 5. Major strike- slip faults. and steep slopes), it presents serious geotechnical geomechanical investigations and detailed studies, problems in the construction of high cut slopes, along with the field data and geological mapping are tunnels and bridges connecting the different sections included in the research project entitled «Geological of the highway. The part of Egnatia highway east of - Engineering Geological Research for the Egnatia Metsovo includes an E-W section reaching Panagia Highway». village, changing subsequently to a N-NE direction. In this part the works that have been constructed so GEOLOGICAL AND TECTONIC SETTING far include 3 tunnels and an 800m long 70m high cut slope. This part also includes the future construction The study area is located in Northern Greece, in of 3 more tunnels as well as a number of valley- the Pindos mountain range. Two distinct geotectonic bridges (Figure 1). units dominate in the area, the Pindos zone nappe Our former investigations of the Egnatia section and the Pindos ophiolite nappe (Figure 2). - Metsovo have dealt with the stability Pindos zone represents the passive margin of the problems of the geological formations and have Neo -Tethyan ocean, composed of Mesozoic attempted to determine the mechanisms that induced carbonate and silisiclastic rocks and the Tertiary them. These investigations have finally determined a Pindos flysch, which forms the main outcrops of the series of tectonic and geomechanical features that in Pindos zone in the area. Pindos zone consists of a our opinion are characteristic of the Pindos area and sequence of Tertiary thrusts including the Pindos are responsible for the creation of these problems. nappe which overthrusts towards WSW the flysch of The purpose of this paper is to confirm that the Ionian and Gavrovo zones (Zouros 1993). above-mentioned features are also existing in the The Pindos ophiolite complex represents part Metsovo - Malakasi - Panagia and investigate fragments of the Neo-Tethyan oceanic lithosphere the mechanical behaviour and the stability problems which was emplaced initially on the western margin of the formations due to these features. The of the Pelagonian zone (Cimerian micro-continent) during Late Jurassic-Early Cretaceous (Mountrakis NNW-SSE in brittle conditions and other major 1983) and subsequently over the Pindos flysch extentional features typical of semi-ductile during Tertiary (Brunn 1956, Zouros et al. 1991). conditions both in the ophiolites and the underlying Pindos ophiolite consists of mafic and ultra- Pindos flysch.. mafic rocks (upper mantle peridotites partly Compressional deformation followed the serpentinised, gabbros, mafic and ultra-mafic previous event, with the maximum stress axes cumulates, sheeted dikes, massive lavas, pillow trending ENE-WSW. This event caused large strike- lavas and basic brecias), metamorphic rocks parts of slip and reverse faults like the ones affecting the the sole (amphibolites, schists and meta-sediments) ophiolites and the flysch along Malakasiotikos river as well as deep sea sediments and turbidites (pelagic valley. limestones, sandstones, calcarenites and micro- A subsequent compressional event with the breccias, siltstones, green and red ribbon and maximum stress axes trending N-S during late nodular radiolarites) (Brunn 1956, Jones & Miocene, produced congugate reverse and strike-slip Robertson 1991, Mountrakis et al. 1992). faults and caused further imbrication of the tectonic A tectonic formation containing blocks of all the units (Kemp & McCaig 1985). above mentioned lithologies occurs along the The neotectonic evolution of the study area seems tectonic contact between the Pindos ophiolite nappe to correspond with the deformation of the broader and the Pindos flysch (Zouros & Mountrakis 1990, area. An extentional tectonism during Pliocene Mountrakis et al. 1992). This formation resembles a followed the compressional deformation. This event tectonic melange which presents a "chaotic" activated NNW-SSE trending normal faults while a structure. The matrix of the melange consists mainly subsequent early to middle Pleistocene extentional of multicoloured shales, siltstone and fine grained deformation formed ENE-WSW to E-W trending sandstones and appears completely sheared. normal faults. This deformation is responsible for Detached blocks of serpentinites, basic volcanics, the present morphology of the area and appears to be cherts, pelagic limestones and deep sea sediments still active as indicated by numerous geological and derived from the ophiolite complex can be observed geomorphological features. within the matrix. These blocks are strongly tectonized and fault bounded. This tectonic GEOMECHANICAL INVESTIGATIONS AND formation was initially created during the Jurassic ANALYSIS subduction-accretion evolution (Jones and Robertson 1991) and probably re-deformed during From the approach mentioned earlier, the the tertiary emplacement of the ophiolites over the geomechanical and general stability problems in the Pindos flysch (Mountrakis et al. 1992). study area, should arise from the presence of the In the northern part of the study area, molassic tectonic formation, the existence of large scale type sediments of the Meso-Hellenic Trough, were strike-slip and normal faults, local rock mass deposited during Oligocene-Early Miocene over the wedging and sliding as well as possible ophiolites and the Pindos zone sediments. combinations of these features. The general attitude of the contact between the As we already mentioned the dominating tectonic Pindos ophiolite nappe and the Pindos flysch seems feature is the emplacement of the ophiolitic rocks to be horizontal to slightly eastward dipping, as the over the Pindos flysch via a tectonic formation lying large number of tectonic windows appearing in the under the ophiolitic complex. study area, including the large semi-window of This formation has a significant horizontal Malakasi confirms. extension under the ophiolitic complex and a Although several studies have been carried out varying thickness which in most cases lies between and different explanations have been given on the 10 to 20 meters. The thickness decreases from the emplacement of the Pindos ophiolites over the west to the east. Pindos flysch, we believe that it took place during an The particle size distribution of the matrix of the important early Oligocene extentional tectonic event tectonic formation is presented in Figure 3 while its that caused a re-deformation of the tectonic melange physical and mechanical properties are included in along the ophiolite-flysch contact. Table 1. The tectonic evolution of the area is complicated. The plasticity and compression index values Structural analysis carried out in the area show that the material presents high risk for (Mountrakis et al 1992) show that several tectonic settlement and sliding (Karlsson 1961, Lambe & events took place. Whitman 1979). The Early Oligocene extentional tectonic event in In addition the correlation of its shear strength an ENE-WSW direction, responsible for the and moisture content presented in Figure 4, shows a emplacement of the ophiolites over the Pindos very rapid decrease in shear strength with the flysch, produced large scale normal faults trending increase of moisture content (Christaras 1991). This formation and its mechanical properties are similar with an analogous tectonic formation along the thrust front of the Pindos tectonic nappe. The presence of the latter has been, in former studies (Christaras et al 1994 & Christaras et al 1995), related with serious stability problems in the Anilio - Anthohori - Votonosi area west of Metsovo.

Figure 4. Correlation diagram between the shear strength and moisture content of the tectonic formation.

The poor mechanical properties of the tectonic formation can lead to a series of stability problems depending on the position of the formation in relation to the road design and the location of the various constructions. In the western part of the study area the road slopes cut mainly through the ophiolitic formations, leaving the tectonic formation Figure 3. Particle size distribution of the tectonic 15-20 m deeper from the road level. Further to the formation matrix. east the thickness of the tectonic formation decreases and combined with the road altitude it Table 1. Physical and mechanical properties of the should not create any stability problems. The tectonic formation. existence of large scale normal and strike-slip faults, however, changes the position of the tectonic Description Moisture Uniform. Permeability formation, bringing it to the road level and in some content coef. coef. cases, to the level of major constructions like tunnels m (%) U K (m/sec) and bridges. In these situations severe construction problems must be expected and this is the case of the Clayey sand 28 >50 10-7 «Malakasi B» tunnel (Figure 5) which encountered (SC-CH) large scale stability problems during the excavation through the tectonic formation.

LL PL Plastic. Group Compres. Bulk (%) (%) index index index density PI GI Cc (t/m3) 60 35 25 13 0.45 1.94

Figure 5: Landslide inside the tectonic formation creating serious stability problems in the excavation of the "Malakasi B" tunnel.

A second category of similar stability problems, mainly landslides and strongly tectonized mass

Figure 6. High cut slope following the northern exit of «Malakasi A» tunnel. 1-3: Rock Mass Quality (Bieniawski 1974 & 1979). 1. Fair (RMR 41-60) 2. Poor (RMR 21-40) 3. Very Poor (RMR 0-20) 4. Unstable material of tectonized zone 5. Unstable material of landslide 6. Embankment 7. Earlier compressive tectonic planes 8. Earlier tensile tectonic planes 9. Normal faults with indication of dip 10. Strike-slip faults with indication of movement 11. Major fault zones 12. Recent open fissures 13. Landslides 14. Active landslides 15. Landslide toe 16. Slope stability analysis (stereographic projection) movements, were encountered in cases where large scale fault zones cut through the road design. As an example we can refer to the high cut slope (800m long, 70m high) following the northern exit of «Malakasi A» tunnel (Figure 6). The large scale landslides activated during the construction of the slope consisted of very strongly tectonized material resembling soil formations. The zones of this material present a general E-W orientation and our investigations have shown that they are actually large scale fault zones created by the E-W strike-slip faults. The extent of these zones reaches some times a width of 50-100m perpendicular to the strike of the faults. Further to the east close to Panagia village a Figure 7: Landslide of a fault zone tectonized major fault of the same direction bounds the contact material in the high cut slope area. between the Sub-pelagonian zone limestones and the accompanying sediments of the ophiolitic series. Major E-W strike-slip faults are combined with This fault zone lies next to the «Kokorelou» tunnel low angle earlier tensile slip surfaces related with which will be constructed near Panagia. the emplacement of the ophiolites. The presence of The stability problems related to the existence of the above mentioned faults along with the NW-SE to these fault zones are, as mentioned earlier, large N-S normal faults, create additional stability scale landslides which in the case of the high cut problems due to strongly tectonized zones in the slope were studied in detail, showing a significant intersections of these faults (Figure 8). extension inward to the slope (Figure 7). This conception altered dramatically the assumption that these zones were surface loose materials created by erosion and weathering of the rock mass and that the problem could be eliminated by simply removing them.

Figure 8: Large normal fault cutting through the ophiolites in the high cut slope area.

A third category of stability problems arise in the cases where these large scale E-W faults are Figure 10: Large scale unstable rock wedge in the connected with the presence of the tectonic high cut slope area. formation.

This is the case of the «Malakasi C» double These calculations show that the formation of tunnel. This tunnel was excavated in the tectonic such rock wedges can create serious construction formation and deep sea sediments accompanying the problems and they should be taken into account in ophiolites. A large E-W trending strike-slip fault is the road design. cutting through the two parts of the tunnel. The fault Aside from the damages and stability problems plane activated a large scale detachment, creating a sustained by the already performed construction landslide that eventually led to the collapse of the works, a series of similar problems are expected to northern branch of the tunnel (Figure 9). arise during the construction of future works Another category of stability problems involves included in the part Malakasi-Panagia. The majority the unfavourable orientations of the smaller scale of these problems will be associated with major discontinuities (fissures, joints, etc). These faults that have been located crossing the tunnel discontinuities affect mainly the parts of the road positions and in some cases the foundations of the design which present better rock mass quality and valley bridges. These faults are mainly E-W and NE- combined with the various slope directions and SW strike-slip faults but also NW-SE normal faults slope angles can give rise to rock wedge sliding or that have created strongly tectonized zones, and they planar failure. are described in detail for every construction The sizes of the rock wedges in the most critical location in the research project mentioned earlier. parts of the road (800m long cut slope) were studied in detail and their safety factors were calculated

(Figures 10, 11).

Figure 11: Stability analysis of rock wedge presented above (Markland 1972, Hocking 1976, Figure 9: Collapsed branch of the "Malakasi C" Hoek & Bray 1981). tunnel, due to the presence of a large fault and the tectonic formation. CONCLUSIONS Bieniawski, Z.T. 1974. Geomechanical Field observations and data analysis confirm the Classification of Rock Masses and Application to presence of the factors affecting the geomechanical Tunneling. Proc. 3d Int. Congr. rock Mechs., behaviour of the geological formations that have Denver, Colo., IIA, pp. 27-32. already been determined from the investigations in Bieniawski, Z.T. 1979. The Geomechanics the Egnatia section west of Metsovo. These factors Classification in Rock Engineering Application. arise from the tectonic emplacement of the Proc. 4th. Congr. Int. Soc. Rock Mech., Montreux, geological formations and the faulting of the broad 2, pp. 41-48. Pindos area and have been summarised as follows: Brunn, J.H. 1956. Contribution a l' Etude The presence and the nature of the tectonic Geologique de Pinde Septentrional et de la formation that lies under the ophiolites overlying the Macedoine Occidentale. Ann. Geol. Pays Hellen., Pindos flysch. This formation has a «chaotic» 7, 1-358 structure with very poor mechanical properties and it Christaras, B. 1991. Casagrande and Fall cone is associated with the creation of landslides and Penetrometer Methods for Liquid Limit stability problems affecting the surface and Determination. Application on Marls from Greta underground constructions along the road design. /Greece. J. Eng. Geol. Elsevier, vol. 31, pp. 131- The E-W strike-slip faults create tectonic zones 142. of significant width. In these zones the rock mass Christaras, B., Zouros, N. & Makedon, Th. 1994. presents a very poor quality and the tectonized Slope Stability Phenomena along the Egnatia material behaves like a non cohesive plastic soil, Highway. The Part Ioannina - Metsovo, in Pindos creating active landslides and rock falls affecting the Mountain Chain, Greece. Proc. 7th Int. Congr. road slopes, as well as the underground Iaeg, Lisboa, in Balkema, Roterdam, pp. 3951- constructions. 3958. The unfavourable orientation of the smaller Christaras, B., Zouros, N. & Makedon, Th. 1995. discontinuities, which daylight on the slopes, create Behaviour of the Votonosi Formation in Pindos unstable rock wedges that in some cases pose Mountain (Greece). Proc. XI ECSMFE serious construction problems mainly for the road Copenhagen ’95, vol. 7, pp. 7.23-7.28 slopes. Hocking, G. 1976. A Method for Distinguishing The combination of the above-mentioned factors between Single and Double Plane Sliding of aggravates the distinct stability problems, leading Tetrahedral Wedges. Int. J. Rock Mech. & Mining some times to the failure and collapse of Sci., 13, pp. 225-226. constructions. Hoek, E. & Bray, J.W. 1981. Rock Slope The nature of the problems mentioned in this Engineering. Inst. Mining & Metal., London: pp. paper makes their prediction essential for the better 1-358. construction and integrity of the designed works. It Jones, G. & Robertson, A. H. F. 1991. Tectono- is therefore necessary to perform detailed Stratigraphy and Evolution of the Mesozoic geotechnical investigations that will focus on the Pindos Ophiolite and Related Units, determination of the specific geological and tectonic Northwestern Greece. J. Geol. Soc. Lond., 148, aspects of the study area. Thus, it will be possible to pp. 267-288. adequately describe the mechanical behaviour of the Karlsson, R. 1961. Suggested Improvements in the geological formations and improve the design of the Liquid limit Test with Reference to Flow various constructions. Properties of Remoulded Clays. Proc. 5th ICSMFE, Paris, vol. 1, pp. 171-184. ACKNOWLEDGEMENTS Kemp, A. E. S. & McCaig, A. M. 1985. Origins and Significance of Rocks in an Imbricate Thrust This work has been supported by the Ministry of Zone beneath the Pindos Ophiolite, Northwestern Environment and Public Works in the frame of the Greece. In: Dixon, J. E. And Robertson, A. H. F. project entitled «Geological - Engineering (Eds.) The Geological Evolution of the Eastern Geological Research for the Egnatia Highway» that Mediterranean., Geol. Soc. London, Spec. Publ., has been carried out by the Laboratory of 17, pp. 569-580. Engineering Geology & Hydrogeology - AUTH Lambe, T.W. & Whitman, R.V. 1979. Soil (DMEO/d/1430/16-10-95). Mechanics, SI Version, John Wiley & Sons, New Furthermore the authors would like to thank Prof. York. D. Moundrakis of the AUTH, for his many helpful Markland, J.T. 1972. A Useful Technique for suggestions during all phases of this study. Estimating the Stability of Rock Slopes when the Rigid Wedge Sliding Type of Failure is Expected. 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