Kandil Concrete-Faced Rockfill Dam and its Response to the 2023 Kahramanmaraş Earthquake Sequence from Strong-Motion Records, Instrumentation, and Underwater Inspection

Abstract This study evaluates the response of the 103-m-high Kandil concrete-faced rockfill dam (CFRD) to the Mw 7.7 Pazarcık and Mw 7.6 Elbistan earthquakes on February 6, 2023, the second of which was 7.3 km away, against the design predictions and known damage mechanisms for CFRDs. Kandil Dam is the only high CFRD for which abutment and crest strong-motion records exist in the near field of the sequence. Data were collected via 190 monitoring instruments, a remotely operated vehicle survey of the face slab joints, and the reconstructed design basis and accelerogram. The abutment motion exceeded the maximum credible earthquake acceleration of the design by a factor of 1.6; however, the scaled design accelerogram was only exceeded for periods of less than 0.3 s. At the fundamental period of the dam, the demand was approximately half the design input, and the crest acceleration remained below the prediction. The fundamental period increased by approximately 30% under strong shaking, consistent with strain-dependent softening of the rockfill without large-scale instability. Permanent downstream movements of the upper shell reached 0.4 m and decayed with depth. Crest settlement was 0.06% and 0.12% of the height at the parapet and crest edge, respectively; residual joint movements were a few millimeters; seepage showed no sustained increase; and the transient increase in foundation pore pressure decayed over days. The slab crushing and seepage increase observed at other CFRDs did not develop. The results provide a benchmark for CFRD verification and support instrumentation, inspection, and reporting requirements near active faults.