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Slope stability along a new road “Drisht –Drisht castle”
Stabilité de pente le long de la nouvelle route "Drisht-Drisht castle"
Paçi E., Cullufi H., Dervishaj A.
Polytechnic University of Tirana, Albania
ABSTRACT: Some slopes along the new road from the village Drisht center to the medieval castle entrance are located in a very
disturbed
tectonic zone. Due to overthrust geological processes the rock quality are extremely poor. In surface there are different
active slides that due to water circulations especially during seismic events are very unstable and slide towards road pavements or
cause side channel and culvert fills.
This article describes the numerical calculation concerning frequent normal conditions during construction and use of road and
accidental condition during seismic events. Based in these calculations design solution are given. The calculations will be controlled
by a back analysis algorithm. We have decided the upper and lower boundaries for the main results and we have made a sensitivity
analysis that will show the influence of each parameter to the predicted results. So during maintenance time with same site tests
results we can correct numerical parameters used in the model and predict long time behavior of the slope. In this manner we can also
correct the future rehabilitation measures (if necessary) for the above mention road slope and other road slopes in similar conditions.
RÉSUMÉ : Certaines pentes le long de la nouvelle route allant du centre du village de Drisht à l'entrée du château médiéval sont
situées dans une zone tectonique très perturbée. En raison de différent processus géologiques, la qualité de la roche est extrêmement
médiocre. En surface, il existe différents glissements actifs qui, en raison de circulations d'eau lors d'événements sismiques, sont très
instables et glissent vers chaussées et remplissent le canal longitudinal.
Cet article présente un calcul numérique (en conditions fréquentes – normales) pendant la construction et l'utilisation de la route. Les
conditions accidentelles correspondant à des événements sismiques sont aussi traitées. Sur les bases des calculs effectués, des
solutions techniques sont proposées. Les calculs sont contrôlés par un algorithme de “back analysis”. Nous avons décidé les limites
supérieure et inférieure pour les principaux résultats et nous avons fait une analyse de sensibilité qui montre l'influence de chaque
paramètre. Ainsi, pendant le temps d'entretien du site, nous pouvons déterminer les paramètres numériques à utiliser dans le modèle
pour prédire le comportement de la pente à long terme. Nous pouvons aussi proposer des mesures de réhabilitation futures (si
nécessaire) pour la pente.
KEYWORDS: Slope stability, seismic events, weathering.
1 INTRODUCTION
The new road links the center of the village with a very famous
medival castle. It pass through a mauntainous area and need a
lot of structures such as retaining walls, culverts, small bridges
etc. The last part of the roads pass in a very steep slope where a
year after the construction ware seen local slope failures.
Figure 1. Photo of local slope failures
The road width is 6m with 0.5 shoulders and a longitudional
concrete paved channel on the side of the mauntain. The road
body is partly in filling and partly in cutting. The zone is one of
the wetest zone in Albania with a average rainfall of
1750mm/year. Due to lack of budget during the construction
phase for finishing all the engineering measures and
maintanence problems during exploitation phase local slope
slides have occured after a period of 3 years.
1.1
Geological and geotechnical aspects
The road to Drisht castle pass through a very disturbed tectonic
zone. The study area takes part in subzone Cukali which, in the
west and northwest is overthrust from the Albanian Alps zone ,
and in the southeast area is overthrust from Mirdita zone. Slope
of the right side of the road represented by mainly constrained
dark color old clays. Inside the clay mass can be meet compact
sandstone layers bodies with dimensions up to 1 m in length,
and up to 30 cm thickness and sandstone pieces measuring 5 to
10 cm with rounded shape and often alienated. These deposits
are turbidits with a clayey - sandy cementation. They are too
weak and are divided into small pieces. The above mention
formation can be classified as very heterogonous flysch. Within
the clay mass at the bottom of the slope (on the right side of the
road) can be meet limestones olistolite size 5 to 10 meters above
which are placed massive limestone rocks of Triassic geologic
time.
