NON-DESTRUCTIVE GROUND PENETRATING RADAR INSPECTION OF HYDRAULIC STRUCTURES USING THE OKO-3 GEORADAR FOR DETECTION OF HIDDEN DEFECTS AND ASSESSMENT OF TECHNICAL CONDITION

Abstract

This paper presents the results of a Ground Penetrating Radar (GPR) survey of the earth-fill dam of the Tasotkel Reservoir located in the Zhambyl Region of the Republic of Kazakhstan. The relevance of the study is associated with the need to improve the reliability and safety of hydraulic structures operating under long-term service conditions and seismic activity. The aim of the study is to evaluate the effectiveness of the GPR method for detecting hidden defects, moisture-rich zones, and local heterogeneities within the dam body and foundation. The investigations were carried out using the OKO-3 Ground Penetrating Radar system equipped with 250, 400, and 900 MHz antennas. A comprehensive inspection algorithm was developed and validated, including collection of initial data, field measurements along longitudinal and transverse survey profiles, digital signal processing, and engineering interpretation of radargrams. Data processing involved dewow filtering, band-pass filtering, signal gain correction, time-zero correction, and migration of reflected signals. The obtained results showed that the dam body is generally characterized by a stable and relatively homogeneous layered structure. Continuous reflecting horizons were identified on most profiles without indications of critical disturbances. Local loosening zones were detected at depths of 0.5-1.5 m, while areas of increased moisture content were identified at depths of 1.0-3.0 m, manifested by signal attenuation and scattered reflection patterns. Hyperbolic anomalies associated with local heterogeneities of the soil mass were recorded on several profiles. The probable contact boundary between the dam body and the foundation was traced at depths of approximately 3.5-4.5 m and exhibited a relatively stable character. It was established that the actual piezometric levels are 3.1-7.2 m lower than the design values, indicating satisfactory seepage conditions and high drainage capacity of the foundation soils.