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Novembre 2010 RSS 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 RSS GENOESE FORT OF TABARKA • North of Tunisia • Build in XVI century • Noticing disorders on structures • Expertise of the stability of the underlying cliff 2 Novembre 2010 RSS 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 3 Novembre 2010 RSS 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 4 Novembre 2010 A current disaster and an under-estimated major risk • Rupture in the South Old disaster RSS 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 5 Novembre 2010 Geological and structural studies • Stratigraphy Sandstones RSS Marls • Structural analysis North section South section 6 Novembre 2010 Expertise of north cliff • 70 m high cliff • Acrobatic means: high mountain guide RSS • Geological and structural analysis 7 • Cliff structure RSS Novembre 2010 Expertise of north cliff 8 • Indications of a cliff recent evolution RSS Novembre 2010 Expertise of north cliff 9 • Differential erosion • Mechanisms of rupture RSS Novembre 2010 Expertise of north cliff 10 • Mechanisms of rupture RSS Novembre 2010 Expertise of north cliff 11 Novembre 2010 Expertise of north cliff • Cliff division into different areas depending on: Fractures family and density RSS Identified mechanisms of rupture • Evaluation of the hazard and the risk Hazard: cliff rupture Risk: impact on the fort structure 12 Novembre 2010 RSS Expertise of north cliff Critère de volume Qualification du volume • Multicriteria analysis Critère de probabilité d’occurrence 1 Probabilité d’occurrence négligeable 2 faible 3 moyen 4 fort 1 faible 2 moyen 3 élevé Fort 4 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 1 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 13 Novembre 2010 Expertise of north cliff • Reinforcement project Longitudinal beam: preservation of the fort RSS Confinement shotcrete: to stop the erosion Nails : stabilization Project presented to the Council of Ministers… Waiting for financing. 14 • Disorders on fort’ structures RSS Novembre 2010 Expertise of South part of fort 15 Novembre 2010 Expertise of South part of fort • Data gathering Drilling RSS Geological structure measurements • Geological and structural model • Earthworks Extraction of rocky materials • History of the fort construction Extensions Filling up 16 Novembre 2010 Expertise of South part of fort • Rupture mechanisms Rock mass: Plane sliding on marls RSS Rock mass: Regressive break Structure of the fort: Internal instability due to earth pressure 17 Novembre 2010 Expertise of South part of fort • Reinforcement project and works Internal earthworks of the fort RSS Passive anchors Nails on the fort walls Micropiles under the fort Nails on the rock mass 18 • Works inside the fort RSS Novembre 2010 Expertise of South part of fort 19 • Works outside the fort RSS Novembre 2010 Expertise of South part of fort 20 • Works outside the fort RSS Novembre 2010 Expertise of South part of fort 21 Novembre 2010 RSS Thank you for your attention 22