ASSESSMENT OF THE TECHNICAL CONDITION OF A DAM LOCATED IN A SEISMICALLY ACTIVE ZONE

Abstract

The aim of this study is to assess the technical condition of a dam in a seismically active zone of Kazakhstan. The object is the pressure front of the Sh. Chokin Kapchagay hydropower plant. It consists of a 52 m hydraulic-fill river-bed dam, a 56 m gravel-rubble ravine dam with a sandy-loam screen, and a quartz-porphyry rock abutment. The dams were designed for intensity 7 (MSK-64), but the site intensity was raised to 8 after the 1988 Spitak earthquake. The materials comprised the dynamic passports of the 2025 survey, settlement records and phreatic curves. The methods included in-situ P and S wave velocity profiling and pseudo-static slope-stability analysis. The seepage regime of both dams is stable. Mean settlement rates are 1.6-2.3 mm/yr for the river-bed dam and 2.06-3.8 mm/yr for the ravine dam, and relative compression does not exceed 0.010 %/yr. Wave velocities and dynamic modulus increase with depth without low-velocity zones. The fractured upper 2 m of the abutment has half the compressive strength of deeper rock. All slopes meet the Class I stability requirements at intensities 7 and 8. At the check intensity of 9, the upstream slope of the ravine dam has K_s = 1.14, 3.4 % below the normative 1.18. It is concluded that settlement is decaying, although the ravine dam has not yet stabilised. The pressure front is stable at the design intensity, and the upstream slope of the ravine dam is its critical element. Dynamic-property profiles of these dams are published for the first time.