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Novembre 2010
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GENOESE FORT OF TABARKA: THE HISTORICAL
HERITAGE THREATENED BY ROCK MASS’
INSTABILITIES
CURTIL Stéphane
HAFFOUDHI Slah Edinne
ZAGHOUANI Kamel
Terrasol
Hydrosol Fondations
Terrasol Tunisie
Novembre 2010
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GENOESE FORT OF TABARKA
• North of Tunisia
• Build in XVI century
• Noticing disorders on structures
• Expertise of the stability of the underlying cliff
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Novembre 2010
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A double analysis: the rocky slope
and the fort structures
• The rocky slope analysis : the natural environment
 Geological analysis
 Structural analysis
 Classical geotechnical approach
• The fort structure analysis: the anthropic environment
 A construction by successive stages: historical analysis
 Analysis of the structure and the visible reinforcements
 Analysis of the visible disorders and the old reparations
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A double analysis: the rocky slope
and the fort structures
• Restrictions induced by the rocky slope
 Difficult access to establish a diagnosis
 Difficult access for the works
• Restrictions induced by the fort
 Cultural heritage – tourist attraction
 Occupied military area
 Brick-built work sensible to deformations
A double approach: geotechnics and civil engineering
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A current disaster and an under-estimated major risk
• Rupture in the South
 Old disaster
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 Reinforcement works since the fort building
 Recent evolution over the last 10 or 15 years
 Visible: studies and works
• Slope general instability in the North
 Under-estimated risk
 Risk of a sudden break
 Invisible: no actions
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Novembre 2010
Geological and structural studies
• Stratigraphy
 Sandstones
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 Marls
• Structural analysis
 North section
 South section
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Expertise of north cliff
• 70 m high cliff
• Acrobatic means: high mountain guide
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• Geological and structural analysis
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• Cliff structure
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Expertise of north cliff
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• Indications of a cliff recent evolution
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Novembre 2010
Expertise of north cliff
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• Differential erosion
• Mechanisms of rupture
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Novembre 2010
Expertise of north cliff
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• Mechanisms of rupture
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Novembre 2010
Expertise of north cliff
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Novembre 2010
Expertise of north cliff
• Cliff division into different areas depending on:
 Fractures family and density
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 Identified mechanisms of rupture
• Evaluation of the hazard and the risk
 Hazard: cliff rupture
 Risk: impact on the fort structure
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Expertise of north cliff
Critère de volume
Qualification
du volume
• Multicriteria analysis
Critère de probabilité d’occurrence
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Probabilité
d’occurrence
négligeable
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faible
3
moyen
4
fort
1
faible
2
moyen
3
élevé
Fort
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Volume pour Volume pour
la falaise
le fort
< 1 m3
quelques
pierres
10 à 50 m3
1 à 2 m3
2 à 5 m3
> 50 m3
> 5 m3
1 à 10 m3
Probabilité d’occurrence
Volume
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2
3
4
1
1
1
2
2
2
1
3
3
3
3
2
3
4
4
4
2
3
4
4
1
2
3
4
Priorités
d’intervention
faible
moyenne
élevée
forte
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Expertise of north cliff
• Reinforcement project
 Longitudinal beam: preservation of the fort
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 Confinement shotcrete: to stop the erosion
 Nails : stabilization
Project presented to the Council of
Ministers… Waiting for financing.
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• Disorders on fort’ structures
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Novembre 2010
Expertise of South part of fort
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Expertise of South part of fort
• Data gathering
 Drilling
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 Geological structure measurements
• Geological and structural model
• Earthworks
 Extraction of rocky materials
• History of the fort construction
 Extensions
 Filling up
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Novembre 2010
Expertise of South part of fort
• Rupture mechanisms
 Rock mass: Plane sliding on marls
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 Rock mass: Regressive break
 Structure of the fort: Internal instability due to earth pressure
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Novembre 2010
Expertise of South part of fort
• Reinforcement project and works
 Internal earthworks of the fort
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 Passive anchors
 Nails on the fort walls
 Micropiles under the fort
 Nails on the rock mass
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• Works inside the fort
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Expertise of South part of fort
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• Works outside the fort
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Expertise of South part of fort
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• Works outside the fort
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Expertise of South part of fort
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Thank you for your attention
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