A REVIEW ON 10 MONITORING GPS SURVEYS OF KARKHEH DAM

Karkheh earth dam is located near Andimeshk, Khuzestan province, Iran, on the Karkheh River. This structure has a total length of 3030 meters and a height of 127 meters, with reservoir capacity of 7.6 billion cubic meters. Because of the large extent of this dam, conventional methods seemed to fail to satisfy monitoring requirements, as they required much time and furnished less accuracy in this case. Besides, earth dams' movements are more substantial than concrete dams. GPS and Microgeodesy group of surveying department of Mahabghods consulting engineers company recommended combining precise leveling vertical networks with GPS horizontal monitoring networks to complete the survey of the dam. These networks are described as follows: GPS-based reference network of the dam region to establish a stable reference frame GPS-based monitoring network to detect horizontal displacements of the dam, using stable points of reference network Leveling network of the dam region, dam itself, galleries and powerhouse The first network with 12 points has been surveyed for 3 times to establish a reference frame to monitor the second network on the dam, which consists of 123 monitoring points. This project has been surveyed in ten epochs to fully monitor movements of the dam. Dual frequency GPS receivers, modern GPS software capable of applying differential methods and adequate configuration were used. By following all pre-requirements, the accuracy of sub-millimeter for reference network and maximum 2.1 millimeter for monitoring network in 95% confidence level was obtained in the last survey, which was satisfactory in the case of earth dams whose displacements are considerable enough with respect to these values. Leveling network consists of 119 points to control the vertical movements of the dam. This network completely meets the vertical monitoring requirements as the maximum accuracy of 0.64 in 95% confidence level was obtained in the last survey. This paper presents these networks; the consistency and applicability of them, especially in large areas and earth dams. It also represents this method as a cost-reducing method without losing accuracy.