GROUND-PENETRATING RADAR DIAGNOSTICS OF THE TECHNICAL CONDITION OF LOAD-BEARING STRUCTURES OF THE KAPCHAGAY HYDROPOWER PLANT UNDER LONG-TERM OPERATION

Abstract

Hydraulic structures deteriorate during long-term operation. Their soil foundations also change over time. Periodic non-destructive inspection is therefore essential. We applied ground-penetrating radar (GPR) to the Sh. Chokin Kapchagay Hydropower Plant on the Ili River, south-eastern Kazakhstan. The plant has operated for over 50 years in a seismic intensity 8 zone. We acquired 62 records with an OKO-3 system using 150 and 400 MHz antennas. Six structural elements were surveyed: the station-adjacent platform, the tailrace canal lining, the upstream slope protection of the channel and ravine dams, the 220 kV outdoor switchyard platform, and the stoplog storage area. Wave velocities were estimated from diffraction hyperbolas. Where possible, they were calibrated against borehole data. Radargrams were interpreted by radar facies analysis. The reinforced-concrete slope protection and canal lining show continuous slab reflections. No major defects or large voids were detected. However, a 35 m section of the canal lining shows differential slab settlement. Loosened soil lies beneath the linings at 0.8-2.0 m depth. Under the station-adjacent platform, intermittent loosened zones reach 1.1-1.9 m. They cover about one third of the profile length. The stoplog storage area is in the poorest condition. Below 3.5 m, chaotic high-amplitude scattering zones 15-16 m wide were identified. They indicate severe soil loosening; voids cannot be excluded. The site has dense surface infrastructure. To avoid false targets, we compared the apparent velocity of each hyperbola with the ground velocity. This separated subsurface objects from reflections off above-ground structures. The results establish a baseline for repeat GPR monitoring.