GENOESE FORT OF TABARKA: THE HISTORICAL HERITAGE THREATENED BY ROCK MASS’ INSTABILITIES

1. GENOESE FORT OF TABARKA: THE HISTORICAL HERITAGE THREATENED BY ROCK MASS’ INSTABILITIES CURTIL Stéphane Terrasol HAFFOUDHI Slah Edinne Hydrosol Fondations ZAGHOUANI Kamel  Terrasol Tunisie

2. GENOESE FORT OF TABARKA • North of Tunisia • Build in XVI century • Noticing disorders on structures • Expertise of the stability of the underlying cliff 2

3. A double analysis: the rocky slopeand 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

4. A double analysis: the rocky slopeand 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

5. A current disaster and an under-estimated major risk • Rupture in the South • Old disaster • 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

6. Geological and structural studies • Stratigraphy • Sandstones • Marls • Structural analysis • North section • South section 6

7. Expertise of north cliff • 70 m high cliff • Acrobatic means: high mountain guide • Geological and structural analysis 7

8. Expertise of north cliff • Cliff structure 8

9. Expertise of north cliff • Indications of a cliff recent evolution 9

10. Expertise of north cliff • Differential erosion • Mechanisms of rupture 10

11. Expertise of north cliff • Mechanisms of rupture 11

12. Expertise of north cliff • Cliff division into different areas depending on: • Fractures family and density • Identified mechanisms of rupture • Evaluation of the hazard and the risk • Hazard: cliff rupture • Risk: impact on the fort structure 12

13. Expertise of north cliff • Multicriteria analysis Critère de volume Critère de probabilité d’occurrence 13

14. Expertise of north cliff • Reinforcement project • Longitudinal beam: preservation of the fort • Confinement shotcrete: to stop the erosion • Nails : stabilization Project presented to the Council of Ministers… Waiting for financing. 14

15. Expertise of South part of fort • Disorders on fort’ structures 15

16. Expertise of South part of fort • Data gathering • Drilling • Geological structure measurements • Geological and structural model • Earthworks • Extraction of rocky materials • History of the fort construction • Extensions • Filling up 16

17. Expertise of South part of fort • Rupture mechanisms • Rock mass: Plane sliding on marls • Rock mass: Regressive break • Structure of the fort: Internal instability due to earth pressure 17

18. Expertise of South part of fort • Reinforcement project and works • Internal earthworks of the fort • Passive anchors • Nails on the fort walls • Micropiles under the fort • Nails on the rock mass 18

19. Expertise of South part of fort • Works inside the fort 19

20. Expertise of South part of fort • Works outside the fort 20

21. Expertise of South part of fort • Works outside the fort 21

22. Thank you for your attention 22