INTEGRATED SEISMIC ASSESSMENT AND SAFETY IMPROVEMENT OF THE KAPCHAGAY HPP DAM, KAZAKHSTAN

The Kapchagay Hydropower Plant (HPP), one of the largest hydraulic structures in Kazakhstan, is located in a seismically active region. This study was conducted in 2000 after an abnormal drop in the water level in the Kapchagay Reservoir was discovered during its operation. A comprehensive investigation was conducted to identify the causes of water losses and assess the operational and seismic safety of the facility. The program included seismic hazard assessment, synthetic accelerogram generation, seismic risk modeling, vertical electrical sounding (VES), underwater inspections, and stability analyses of the riverbed and saddle dams. Based on geological, geophysical, and seismotectonic data, the characteristics of potentially hazardous seismogenic zones were refined and design seismic loading scenarios were developed. The results showed that the Zailiysky seismogenic zone represents the most critical seismic source for the site, producing a peak ground acceleration of 205 cm/s², corresponding to an intensity of 8 points on the MSK-64 scale. Stability analyses confirmed that both dams satisfy the safety requirements for Class II hydraulic structures at the recommended normal retaining water level of 479 m. VES investigations identified seepage-related anomalies, which were subsequently confirmed through underwater inspections. Pressure grouting of the weakened zone eliminated abnormal water losses and improved the reliability of the hydraulic structures. The study demonstrates the effectiveness of integrating seismic hazard assessment, risk analysis, geophysical diagnostics, underwater inspections, and engineering remediation within a unified framework for hydraulic structure safety management.