GPR SURVEYS AT SOME 700 YEARS-OLD STRUCTURES IN THE OLD CITY OF CAIRO, EGYPT.

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1 GPR SURVEYS AT SOME 700 YEARS-OLD STRUCTURES IN THE OLD CITY OF CAIRO, EGYPT. Mohamed G. El-Behiry Geophysics Department, Faculty of Science, Cairo University, Giza, Egypt. Abstract Remediation and restoration plans of the Ancient Egyptian Heritage are currently taking much attention from local governmental and international organizations. Khan El-Khalily region, which is located in Al Azhr area, is one of the important archeological places in the old city of Cairo. It contains several famous structures (such as palaces, schools, graves, houses, and fountains) that had been built seven centuries ago. Such constructions are now suffering from fluctuations of groundwater and increasing ambient vibrations due to daily human activities as well as traffics. Several incidents for wall-collapse, ground subsidence, buildings differential settlement, and elevated groundwater were reported in Khan El-Khalily region. Information on subsurface conditions, such as presence of voids, water tanks, foundations, and antiquities, at these structures are considered valuable for the designed remediation and restoration plans. The non-destructive GPR-surveys, using 500 MHz antenna, were performed at three selected sites in Khan El-Khalily region. At each site, a CMP-survey was conducted to determine the radar-wave velocity. The interpreted radar records of the first site, which represented by a palace, could differentiate between subsurface fill-materials (silt and rock fragments) and cement fill that found at depth interval of m. Remains of buried foundations could also be mapped at depth of 2.7m. The second site is a conference hall that contains ancient fountain in its center. The fountain itself was surveyed by using flat wooden sheets. GPR-records showed the pipe that had been used to supply water to the fountain. The third site is an ancient grave of important value to the Middle Egyptian History. Several supporting pillars and even the stairs leading to the grave entrance could be mapped from GPRrecords. Introduction Most of the Egyptian Islamic heritage has been gathered in Cairo. Khan El-Khalily region, which lies at the middle-eastern part of the city of Cairo, is very famous with a collection of ancient Mosques, Palaces, Schools, Graves, and other constructions of important historical values. The age of these constructions range between 1300 and 1400 AD. Since Khan El- Khalily region is one of the oldest and well-known commercial places in Cairo, it is characterized by high inhabitants who are working in trade and tourist businesses. Daily human activities and traffics of such crowd are severely affecting the general conditions of the existing historical constructions. Several incidents for wall-collapse, ground subsidence, and buildings differential settlement due to elevated groundwater were reported in Khan El-Khalily region. Currently, the Egyptian government with the help of international and local organizations are concerned with the remediation and restoration programs for the threatened constructions. The planned efforts were to (1) non-invasively map buried structures and inhomogenities at three selected sites, and (2) the archaeological team needed interpretations in near real time to guide their excavations. The ground penetrating radar (GPR) techniques was selected for use in this study. The GPR-method was selected because the workable areas in the three sites are isolated and of limited areal extent. Furthermore, the non-destructive GPR-technique reveals a real-time data that can help archaeologists in their excavations and design for supporting foundations.

2 The present paper demonstrates the preliminary results of GPR-surveys performed at the selected three archaeological sites in Khan El-Khalily region, Cairo, Egypt. The Sites Three sites are considered in the present study. The first site (Fig. 1a) is a palace that has been used as the Cairo-governor official palace about 696 years ago. It occupies an area of 31m x 17.5m and consists of two levels; the lower one contains reception hall that leads to four rooms, and the upper level an open space above the rooms that has been used as governor office. Soil subsidence in the hall and differential settlement of pillars supporting the upper level were reported in this site. The second site (Fig. 1b) has been used as a school and conference hall. It occupies an area of 245 m 2 and consists of four classrooms and a hall with its middle part occupied with ancient fountain. Deterioration of walls and soil subsidence due to elevated groundwater were reported in this site. The third site (Fig. 1c) is an ancient grave of a well-known Egyptian king of the Middle Egyptian Islamic age. The site has an area of about 596 m 2 and consists of a grave room with a tag in its middle part and a couple of small rooms. Soil subsidence in many places in the grave room and deterioration of walls are characterizing this site. Restoration and remediation plans of this site recommend the movement of the grave from its place in order to restoring the grave from inside and constructing supporting pillars to prevent it from collapsing. Ground-Penetrating Radar Surveys Several workers have used GPR-technique to solve problems in archaeological sites. For example, Lawrence and Goodman (1997) have discussed the basic concepts of GPR for archaeologists. Goodman et. al., (2002) used 500 MHz radar antenna to detect near-surface Roman amphitheater structures and other deeper structures using time slice analysis; Mundell et. al., (2002) used an integrated GPR, resistivity, and magnetic techniques to test the efficacy of geophysical methods for pre-evaluating suspected Anasazi ruins within selected areas of a prehistoric archaeological complex site prior to archaeological excavation. Campbell et. al. (2001), Conyers (2001), and El-Behiry (2002) among others, have also used GPR for archaeological applications. In the present study, three CMP-radar surveys were conducted at the three sites in order to estimate the EM-wave velocity values that are used to convert the reflection travel time of radar-waves into the corresponding depth. The calculated velocities of the three sites are 10.87, 15.43, and 12.2 cm/ns, respectively. Using a 500 MHz radar antenna, closely spaced parallel profiles were collected at a 1.0- meter spacing across the three sites. Figures (2, 3, and 4) show the 500 MHz antenna in operation mode at the workable spaces in the first, second, and third sites, respectively. In the first site, areas with limited areal extent were frequently encountered (Fig. 2a). In the second site as shown in Figure (3c), wooden plates were used in order to be able to survey the fountain itself to detect subsurface water tanks. In the third site, however, a vent is observed (Fig. 4b) indicating the location of buried stony water-filled tank that was surveyed later from inside by divers. The collected radar records were good such that only the available FIR-filter with a band window of 5-30 Hz was used for data enhancement.

3 The Results The preliminary results of the performed GPR-surveys are summarized in the following: I- The first site: the scattered reflections indicate to the existence of subsurface noncompacted fill materials to a depth of about 1.5m that have been partially replaced with cement (Fig. 5a) that appears as high amplitude events. Buried foundations could be detected at depth of about 2.7m (Fig. 5b). Subsequent excavations revealed the existence of these foundations (Fig. 5c) buried in moist silty soil. II- The second site: the most important issue in this site is the delineation of buried water tank and pipes that support the fountain. Surveying the fountain itself using wooden plates resulted in GPR-images showing no indication to buried tanks. Buried pipe could however be detected (Fig. 6) at the lower left corner of the fountain at depth of 1.8m. Several small subsurface voids could also be outlined in this site. III- The third site: Due to the observed sever soil subsidence in this site; it was afraid that a sudden collapse of the grave would take place. Therefore, the first priority was to map the grave boundary and delineate the grave contents. The existence of the heavy wooden grave tag limited much of the workable space. Figure (7a) shows subsurface supporting pillar that extends from about 0.8 to 2.0m deep and capped with the grave ceiling roof (about 0.3m thick) that exist at depth of 0.5m. Figure (7b) shows part of buried stairs that lead to the grave entrance. These stairs are located to the left of the existing grave tag. Summary and Conclusions GPR-surveys are performed at three selected archaeological sites (about 700 years old) in Khan El-Khalily region, which located in the old city of Cairo Egypt to assess subsurface conditions required for remediation and restoration plans of these sites. Preliminary GPR-results revealed different subsurface inhomogenities at the three sites. In the first site, places with subsurface fill materials (silt and rock fragments) could be differentiated from those filled with regular cement. Buried foundations confirmed with subsequent excavations, could also be detected at this site. The second site, which contains fountain in its middle part, shows no indication to buried water tank underneath the fountain. Buried pipe could however be detected at the lower left corner of the fountain at depth of 1.8m. The main target for surveying the third site was to map the boundary of the existing grave. Subsurface supporting pillar capped with the grave ceiling roof could be delineated from GPR-images. Even so, part of the buried stairs that lead to the grave entrance could also be mapped to the left of the existing grave tag. In conclusion, the non-destructive GPR-technique offered great help for archaeologists to figure out subsurface conditions at archaeological sites. References Campbell, D. L., Beanland, S., Lucius, J. E. and Powers, M. H., 2000, Magnetic and GPR Surveys of a Former Munitions Foundry Site at the Denver Federal Center, in Proceedings, SAGEEP 2000, Symposium on the Application of Geophysics to Engineering and Environmental Problems, Arlington, Virginia, February 20-24, 2000, pp Conyers, Lawrence B. and Dean Goodman (1997), GPR: An Introduction for Archaeologists, ISBM , Alta Mira Press, Sage Publications. Conyers, L. B., 2001, Ground-penetrating Radar Amplitude Analysis for Archaeological Applications. In Proceedings, SAGEEP 2001, Symposium on the Application of Geophysics to Engineering and Environmental Problems, Denver, Colorado, March 4-7, BCF-3.

4 El-Behiry, M. G., 2002, GPR and subsurface targets. In Proceedings, SAGEEP 2002, Symposium on the Application of Geophysics to Engineering and Environmental Problems, Las Vegas, Nevada, Feb Goodman, D., Piro, S., and Nishimura, Y., 2002, GPR Survey Discovers Lost 1st Century AD Roman Amphitheater. In Proceedings, SAGEEP 2002, Symposium on the Application of Geophysics to Engineering and Environmental Problems, Las Vegas, Nevada, Feb Mundell, J. A., Byer, G. B., Henson, H., Gutowski, V., and Dove, D. E., 2002, The use of geophysical surveys for archaeological excavation planning at the Mitchell Springs Ruins in Cortez, Colorado. In Proceedings, SAGEEP 2002, Symposium on the Application of Geophysics to Engineering and Environmental Problems, Las Vegas, Nevada, Feb (c) Fig. 1: Site maps of the GPR-surveyed three sites at Khan El-Khalily region, Cairo, Egypt. R1, R2,.. are designated for rooms.. Fig. 2: 500 MHz antenna in operation mode at the workable spaces of the first site.

5 (c) Fig. 3: GPR-system in operation mode at the workable spaces of the second site. (c)wooden plates were used to survey the fountain. Fig. 4: GPR-system in operation mode at the workable spaces of the third site. Lower photo shows a vent of subsurface water-filled tank.

6 (c) Fig. 5: Selected GPR-images of the first site showing cement fill, soil subsidence above buried foundations, excavations confirming existence of buried foundations (c). Fig. 6: GPR-image from the second site showing the location of the buried pipe that supplied the fountain with water. Fig. 7: GPR-images from the third site showing the existence of buried ceiling roof capping supporting pillar and buried stairs that lead to the grave. 219