Geotechnical Study for Evaluating Stability and Restoration Work at the 1,000 Year Old Archaeological Site of Ayla, Gulf of Aqaba, Kingdom of Jordan

Abstract

Geotechnical Investigations at the site of ancient Ayla in Aqaba, Jordan, show that soils are predominantly granular, with archaeological fill overlying beach sand, which in turn overlies a coarser sand and gravel. Except for the wadi area, ground water occurs about 3 m below the existing ground level. The bearing capacity of the foundation is 3.5 kg/cm 2 for the dense granular materials that represent the probable founding layer of the existing walls, and 2.0 kg/cm 2 for the weaker silty/clayey zone. Back analysis yields a safe wall height of at least 6.0 m. Therefore, no stability problems are present. Tilting and sinking were noted in some portions of the exterior walls as a result of dynamic lateral earth pressures caused by a major earthquake incident in 1067 A.D. Thus, wall-foundation support is recommended during archaeological excavations; and permanent excavations for exposing the walls should be limited to about 3 m by the western wall, and about 2.5 m by the eastern wall. Stones used in the construction of ancient Ayla consist of precut sandstone, siltstone, mudstone and granite. Weathering effects were clearly noted on the exposed stones on the walls. The replacement stone should consist of sandstone blocks located 35 km north of Aqaba. Wall restoration includes replacement of mortar in the inner walls and disintegrated stone pieces in the external walls. Existing mortars consist primarily of a brown silty mixture and a gray mixture, but also a mixture of fine gravel, and a lime/gypsum binder. The major chemical constituents of the original mortar are 18 percent SiO 2 , 23 percent CaO, and 34 percent SO 3 . X-ray diffraction peaks indicate the presence of gypsum, calcite and quartz. Comparative analysis data gave 7 percent CaCO 3 , 53 percent sand, and 40 percent solubles as average values for the constituents. Two sand sources were identified for the mortar mix; recommended mortar for restoration was a mix of lime, sand, and ash, with ratios of 1:3:1.5.