Soil properties, foundation stability, groundwater conditions, characteristics of building stones and mortar used in construction and proposed measures for restoration at the site of ancient Ayla in a Qaba, Jordan

Ancient Ayla in Aqaba, Jordan was destroyed during a major earthquake incident that occurred in Aqaba in 1067 AD. The Gulf of Aqaba is a seismically active region. The latest strong earthquake incident occurred on November 22, 1995 when an earthquake of local magnitude 6.2 rocked the Gulf of Aqaba region. The main shock was followed by thousands of aftershocks. The Gulf of Aqaba-convering the geologic coordinates 28.0–29.6 N; 34.5–35..2 E is one of two natural bays surrounding the Sinai Peninsula which itself is located at the northernmost end of the Red Sea. The soil profile underlying Aqaba city consists of interlayering of various sedimentory Holocene Alluvium deposits. This study is aimed at investigating the soil and foundation condition at the site of the ancient Ayla. This includes groundwater conditions, bearing capacity of the strata supporting the walls of ancient Ayla, and structural stability of these walls. The study included an investigation of the characteristics of building stones used in the earlier construction as well as those proposed for use in the restoration of Ancient Ayla. Furthermore, the physical and chemical properties of existing mortars were evaluated. Gradation analyses were conducted to select a proper sand for use in the mortar mix. Mortar mix tests were conducted for the purpose of recommending a mortar mix for use in restoration works. Trends in the results of various mix tests were analyzed. Sample borings were made at the site to obtain soi profile and extract soil and water samples. Standard Penetration test was conducted at different depths. Laboratory tests were performed on these samples to determine pertinent physical properties of the soil and salinity of the water. Soils at the site were found to be predominantly granular with archaeological fill overlying beach sand which in turn overlies the coarser sand and gravel of the natural deposits. Except for the wadi area, groundwater was encountered at about 3 m below existing ground levels. Bearing capacity of the foundation was evaluated to be 3.5 kg/cm² for the dense granular materials (that represent the probable founding layer of the existing walls), and 2.0 kg/cm² for the weaker silty/clayed 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 exerted during the major earthquake incident of 1067 AD. Measures for wall foundation support during archaelogical excavations are suggested. Permanent excavations for exposing the walls should be limited to a free height of about 3 m at the location of western wall, and about 2.5 m at the location of the eastern wall. Stones used in the construction of ancient Ayla were found to consist of precut sandstone, siltstone, mudstone and granite. Weathering effects were clearly noted on the exposed stones in the walls. It is proposed to use a replacement stone consisting of sandstone group located at a source 35 km North of Aqaba. Measures suggested for the restoration of the walls addressed the lack of mortar in the inner walls and the replacement of disintegrated stone pieces in the external walls. Existing mortars were found to consist primarily of three types, namely a brown silty mixture, a gray mixture, but predominantly a mixture of fine gravel and a lime/gypsum binder. The major chemical constituents of the original mortar are 18 % SiO₂, 23 % CaO, and 34 % SO₃. X-ray diffraction peaks indicate the presence of gypsum, calcite and quartz. Comparative analysis data gave 7 % CaCO₃, 53 % Sand, and 40 % Solubles as average values of the constituents. Following the selection of two sand sources for use in the mortar mix, recommended mortar for restoration was a mix of lime, sand, ash, with ratios of 1:3:1.5.