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The Early Phrygian Gate at Gordion, Turkey An Investigation of Dry Laid Masonry in Seismic Regions Meredith Keller, University of Pennsylvania [email protected] 6 0 3 Meters Legend Crack Open Joint Ground Missing Spall Split Face Bulge Grout Backfill Legend Ground 6 0 3 Meters First excavated in the 1950s by a team of archaeologists from the University of Pennsylvania Museum of Archaeology and Anthropology, the Early Phrygian Gate is the largest extant masonry gate to survive from the Iron Age in the Middle East. However, its dry laid construction (built without the use of mortar) leaves it vul- nerable to the region’s high seismic activity. Constructed around 900 BCE, the Early Phrygian Gate served only briefly as the main entryway to the citadel. Suc- cessive periods of occupation within the citadel mound resulted in further building campaigns which utilized the earlier structures as foundations for new construc- tion. The changing load patterns produced by the new structures caused a series of visible conditions—most notably cracking and displacement—discovered upon excavation. Although cracking occurred historically from the additional loads of the later city walls, displacement continues to be an active condition. From 2006-2010, the University of Pennsylvania’s Architectural Conservation Laboratory (ACL) has conducted a detailed program to document, monitor and assess the gate’s overall structural stability and determine the condition of its limestone and rhyolite walls. Only partially exposed during excavation, the gate’s South Court retains the original expansive clay construction fill in its interior—the result of the subsequent Phrygian building campaign. The clay fill, in addition to the settlement of core material, has contributed to several areas of displacement. Since its exposure to the environment approximately six decades ago, the gate has been subjected to several localized re- constructions, as well as a gravity injection grouting program to address movement and stabilize the ancient walls. Although the gate has largely maintained its original aesthetic, areas receiving these interventions exhibit variations in chinking technique and, in some cases, stone type. Concrete capping, like the grouting program, has been implemented as a reactive measure to inhibit water ingress and prevent further bulging; however, a more diagnostic approach was necessary to respond to ongoing displacement and possible collapse, which may result from future seismic activity. Starting in 2006, the ACL developed an extensive documentation program, which included a digitized condition survey of each exposed elevation to re- cord spalls, open joints, missing chinking stones and bulging, and in 2009 con- ducted high-density laser imaging with a mid-range Trimble VX100 laser scanner. Results of the documentation process indicate that many visible conditions occurred historically. Comparisons made between images taken during the 1950s excava- tion and the 2006 condition survey show a correlation between the additional Middle Phrygian building load and the innumerable compression cracks found below ex- tant Middle Phrygian courses. However, the 1950s images reveal that the great- est degree of displacement—visible by the large, central bulge of the South Court elevation—occurred more recently. A method to quantify displacement in this po- tentially unstable region has recently been implemented through a joint effort be- tween Middle East Technical University and the Architectural Conservation Labo- ratory. The monitoring program, which will determine whether bulging is resulting from constant incremental movement or only displacing during seismic events, is critical to the design and execution of a stabilization program for the gate structure. 6 0 3 Meters Legend Crack Open Joint Ground Missing Spall Split Face Bulge Meters DOCUMENTATION DOCUMENTATION NORTH COURT NORTH COURT CONDITION CONDITION SOUTH COURT SOUTH COURT North Court South Court N Although signs of displacement (apparent through cracking and open joints) were evident in the South Court wall, the gate appeared stable following excavation in 1955. Source: Penn Museum Gordion Archive The 2009 image indicates that a great deal of core settlement has occurred and has resulted in the large, central bulge at the ramp to the citadel interior. A North and South Court comprise the Citadel Gate with a central entryway extending between the two pylons and leading to the citadel interior. Walls highlighted in red in- dicate elevations shown in the condition survey below. Source: Architectural Conservation Laboratory Laser scanning was employed by the Architectural Conservation Laboratory (ACL) to accurately document and quantify the bulging area. Source: ACL Below: For nearly three thousand years the interior North Court eleva- tion served as the foundation for a Middle Phrygian Gate wall. Several courses from this later structure remain atop the earlier building, which exhibits a great deal of compression cracking, as well as open joints and a slight bulge. Because these conditions occurred historically, ac- tive displacement appears to be minimal—even with unexcavated fill adjoining the exterior face. Below right: In contrast, the exterior South Court elevation shows significant active displacement resulting from both settlement of the wall’s rubble core material and the lateral force exerted by confined Middle Phrygian construction fill within the court interior. Source: Architectural Conservation Laboratory 6 0 3 Meters Legend Ground Backfill 2010 Istanbul Congress Conservation and the Eastern Mediterranean Early Phrygian Gate Plan
