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. Greece) 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). Ioannina - 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