Settlement and slaking problems in the world's fourth largest rock-fill dam, the Ataturk Dam in Turkey

The Ataturk Dam is the fourth largest clay cored rock-fill dam in the world . Located in southeastern Turkey, it is the centrepiece of a project called the Southeastern Anatolian Project (GAP). The construction of the dam was finished in the short time of 3 years and 8 months in August 1990. As the r eservoir level started to rise, settlement problems started to occur along the crest reaching considerable levels by May 1992 and the weathered vesicu lar basalt used in the rock-fill section of the dam started to slake seriou sly. The elevation of the crest has fallen down to such an extent that now the upper part of the dam is being reconstructed to the original height of 549 m in order to maintain the 7 m freeboard and keep the dam operational. The settlement and slaking problems of the dam were investigated both in th e field and the laboratory using soil and rock mechanical techniques. Stand ard proctor tests were run to determine tbe optimum moisture content at whi ch the highest dry density (best compaction) is obtained during compaction of the impervious clay core. Consolidation tests were performed on undistur bed compacted clay core samples to determine if the field compaction of the clay core was done to the standards determined in the laboratory. Unconfin ed compression tests were run on the two different (sound aphanitic and wea thered vesicular) basalts used in the rock-fill section of the dam to deter mine their unconfined compressive strengths. Slake durability tests were ru n on the same basalts to determine their durability under wetting and dryin g cycles. Petrographic and X-ray analysis were done so as to study the mine ralogical contents of the two basalts and in turn, to determine the cause o f rapid slaking of the vesicular textured weathered basalt. The consolidati on test results show that, the field compaction of the impervious clay core of the dam was not done to the standards determined through the proctor te sts in the laboratory. The unconfined compressive strength of the sound aph anitic basalt is more than ten times greater than the weathered vesicular b asalt, and while the former has extremely high durability the latter only h as medium durability. Because of nontronite (iron montmorillonite) and seco ndary calcite amygdules filling the vesicles, the weathered vesicular basal t used in the rock-fill section is slaking badly causing additional settlem ent and landslides both in the clay core which is already settling and the rock-fill section of the dam. With the continuing slaking, the present reco nstruction of the crest up to the theoretically intended height of 549 m to maintain the 7 m freeboard and keep the dam operational seems only to be a temporary solution. (C) 2000 Elsevier Science B.V. All rights reserved.