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The Early Phrygian Gate at Gordion, Turkey
An Inves t iga t ion o f Dry La id Masonry in Se ismic Reg ions
Meredith Keller, University of [email protected]
60 3Meters
Legend
Crack
Open Joint
Ground
Missing
Spall
Split Face
Bulge
Grout
Backfill
LegendGround
60 3Meters
First excavated in the 1950s by a team of archaeologists from the University of Pennsylvania Museum of Archaeology and Anthropology, the Early Phrygian Gateis 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, theEarly Phrygian Gate served only briefl y as the main entryway to the citadel. Suc-cessive periods of occupation within the citadel mound resulted in further buildingcampaigns which utilized the earlier structures as foundations for new construc-tion. The changing load patterns produced by the new structures caused a seriesof visible conditions—most notably cracking and displacement—discovered uponexcavation. Although cracking occurred historically from the additional loads of thelater city walls, displacement continues to be an active condition. From 2006-2010,the University of Pennsylvania’s Architectural Conservation Laboratory (ACL) hasconducted a detailed program to document, monitor and assess the gate’s overallstructural stability and determine the condition of its limestone and rhyolite walls.
Only partially exposed during excavation, the gate’s South Court retains the originalexpansive clay construction fi ll in its interior—the result of the subsequent Phrygianbuilding campaign. The clay fi ll, in addition to the settlement of core material, hascontributed to several areas of displacement. Since its exposure to the environmentapproximately six decades ago, the gate has been subjected to several localized re-constructions, as well as a gravity injection grouting program to address movementand stabilize the ancient walls. Although the gate has largely maintained its originalaesthetic, areas receiving these interventions exhibit variations in chinking techniqueand, in some cases, stone type. Concrete capping, like the grouting program, hasbeen implemented as a reactive measure to inhibit water ingress and prevent further bulging; however, a more diagnostic approach was necessary to respond to ongoingdisplacement 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 occurredhistorically. Comparisons made between images taken during the 1950s excava-tion and the 2006 condition survey show a correlation between the additional MiddlePhrygian 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 Courtelevation—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 resultingfrom constant incremental movement or only displacing during seismic events, iscritical to the design and execution of a stabilization program for the gate structure.
60 3Meters
Legend
Crack
Open Joint
Ground
Missing
Spall
Split Face
Bulge
Meters
D O C U M E N T A T I O ND O C U M E N T A T I O N
N O R T H C O U R TN O R T H C O U R T
C O N D I T I O NC O N D I T I O N
S O U T H C O U R TS O U T H C O U R T
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. Severalcourses from this later structure remain atop the earlier building, whichexhibits a great deal of compression cracking, as well as open jointsand a slight bulge. Because these conditions occurred historically, ac-tive displacement appears to be minimal—even with unexcavated fi lladjoining the exterior face. Below right: In contrast, the exterior SouthCourt elevation shows signifi cant active displacement resulting fromboth settlement of the wall’s rubble core material and the lateral forceexerted by confi ned Middle Phrygian construction fi ll within the courtinterior. Source: Architectural Conservation Laboratory
60 3Meters
Legend
Ground
Backfill
2010 Istanbul CongressConservation and the Eastern Mediterranean
Early Phrygian Gate Plan