Experiences of consolidation on archaeological UNESCO sites in Sultanate of Oman: the Fortress of Al Balid and the Citadel of Sumhuram

Taking the opportunity to collaborate with the archaeological groups a staff of structural en-gineers has been organized to attend the consolidation works on the UNESCO sites of Khor Rori and Al Balid (Sultanate of Oman). Starting from early 2005 a series of missions have been managed to restore the ancient city walls of Sum-huram in the site of Khor Rori and other structural elements, establishing the appropriate procedures and co-ordinating the workmen involved during excavations, together with the archaeological Italian Mission To Oman of the University of Pisa,. The site is characterized by a cave of limestone, used for the city walls, and a soil with high percentage of clay, used to infill the block joints and the space between the external stone faces. The two faces of walls were not well transversally connected and the internal filling was made by clay soil: during the rain seasons the filling reduced its consistence causing progressive collapse situations. The rebuild-ing activity of walls has been involved to give safety along the path for visitors, replying the same texture of the stones adding internal transverse stone connections (“orthostati”), accompanied by a proper choice of the mortar (colour, composition and strength) to reply the original joint aspect and filling the walls with a mix with superior permeability. The re-constructed walls has been separated by the original with a geotextile foil. A simplified analytical model has been then prepared to evaluate the increment of safety level due to the con-solidations, assigning the shape of the collapse surfaces and adopting a simplified approach of limit analysis. In the same period members the group have been involved to consolidate the Fortress in UNESCO site of Al Balid in the nearby (Salalah – Sultanate of Oman) erected about 1100 A.D.; the excavations was managed by the Institute of Archaeology of the Missouri University. In this case the absence of mortar did not cause collapses, while the resistance has been ensured by the gravity loads and friction of stones; the collapse has been originated by the loss of permeability of the external wall faces due to the progressive filling of joint by soil. Therefore consolidations consisted to excavate and immediately rebuild the collapsed walls with the same blocks down, after the substitution of the earth behind the external layers remaking a drainage made of mixed gravel and small stones selected on site to ensure an efficient washout during rain seasons. Unoriginal ramps to penetrate inside the Fortress has been removed with accurate excavation, reducing transverse loads due to the unbalanced earth pressure. A simplified model to evaluate the behaviour of walls has been per-formed to describe failure mechanism and the influence of the main physical and geometrical parameters.