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The Tsakona landslide in the Peloponnese, Greece

Autori: 
Belokas G., Dounias G.
Numero: 
1
Anno: 
2016
Pagina: 
34

In February 2003 a complex movement of a deep translational slide accompanied by a surficial soil flowing movement caused one of the largest motorway landslides in Greece. Geotechnical investigations in 2000-2001, before this catastrophic event, had already revealed a soil slope deformation, of about 680 m length and 2.500.000 m3 volume, moving at a slow rate. The moving materials were mainly surficial deposits (including embankments and fills), while the deep movements were developing mainly within a weathered flysch above the flysch bed-rock, at depths varying from about 20 m to 35 m. Although the displacement rate was low, acceleration could not be avoided in this environment, modified by a combination of geological processes and manmade interventions. In the Tsakona case, a prolonged very wet season most probably provided the final trigger of an already precarious stability condition. This major event occurred in February 2003 and expanded the limits of the landslide down to the riverbed, locally blocking the river flow. Notably, about 200 m of the carriageway slipped for approximately 100 m in plan and 40 m vertically. At this stage, the landsliding material amounted to 1050 m length and 6.000.000 m3 volume. Movements were negligible after the end of the major event. This paper examines the various natural processes and manmade interactions that affected the stability of the slope. Concerning the remediation works, a deviation from the landsliding area via a tunnel through the mountain or going over the landslide with a bridge, would provide sufficient safety at an acceptable cost. The bridge solution was finally adopted.