Assessment of Vertical Deformation of the Atatürk Dam Using Geodetic Observations

Abstract

The Atatürk Dam in Turkey, constructed on the Firat River, is one of the world’s largest rockfill embankment dams. It was built to harvest and conserve water and to serve crucial agricultural, social-economic, recreational, and other activities in the Harran region. In this study, geodetic techniques were exploited to assess possible deformations of the embankment structure and add insight on critical dam safety. The geodetic approach included differential, trigonometric, and global positioning system (GPS) leveling observation campaigns over a period of 6.5 years from May 2006 through November 2012. The geodetic control network included 32 reference points and approximately 200 object points located on the surface of the embankment structure. The primary object points were stable concrete platforms embedded on the compacted rock surface, whereas the secondary object points were mounted directly to the compacted rock. All object points were equipped with forced centering mechanisms to support either optical targets, reflectors, or GPS receivers, depending on the type of geodetic measurement campaign. Collected data from different geodetic techniques and results were processed and analyzed. An intercomparison of the results suggests that settlement of the crest reached a maximum of more than 30 cm near the middle of the river. The settlement pattern of the object points on the centerline and upstream side of the crest may suggest shear slump on the clay core with an average of roughly 5 mm/month. The downstream side of the embankment crest appears more stable, with small vertical movement amplitudes (< 10 cm). Fluctuation in reservoir water level, due largely to water management decisions, seems to suggest that variations in water load were unrelated to the embankment surface deformation. On the other hand, the fluctuation in the reservoir water level may have induced variations in the pore pressure of the inner clay core, which in turn may have weakened and caused a slumping on the inner clay core along the centerline and upstream sides of the embankment crest. It is difficult to make definitive claims on the small-amplitude volumetric changes of the downstream embankment surface because the amplitudes of estimated point deformations approached the measurement accuracy limits. However, results indicate that displacements of object points at lower elevation near the thicker base of the downstream embankment surface were more stable than points located higher up, where the embankment is less insulated from mass shifts of the inner clay core. Furthermore, this study supports the notion that GPS leveling can be a viable alternative for monitoring the vertical deformation of large structures when traditional geodetic methods prove too costly.