Non-Destructive Testing Techniques for Condition Assessment of Reinforced Concrete Overhead Transmission Foundations

Overhead line (OHL) support structures typically rely on shallow reinforced concrete foundations that become difficult inspect once buried, significantly limiting direct inspection and condition assessment. This creates significant uncertainty during refurbishment and life extension activities, often resulting in conservative design assumptions or premature replacement. Support structure concepts that prioritise inspect ability, modularity, and whole life performance therefore present a clear opportunity to reduce risk and improve the long-term sustainability of OHL infrastructure. For lattice towers, foundations are typically embedded at depths of approximately 1.5 – 3 m, depending on soil conditions and loading requirements. Full excavation of these foundations is generally avoided, as it can compromise both uplift capacity and lateral resistance. Consequently, non-destructive testing (NDT) becomes the primary means of assessing the condition of the existing foundations. This study introduces a safetyoriented NDT assessment framework for overhead power line foundations, applicable to both pad and pad and pedestal foundation types. The framework explicitly accounts for the influence of soil moisture, type, and chemically aggressive environments. This application was demonstrated through a case study involving thirteen reinforced concrete columns in a chemically harsh environment. The proposed workflow assesses the condition and integrity of the existing structure through a combination of visual inspection, rebound hammer testing, ultrasonic pulse velocity (UPV), ground-penetrating radar (GPR) and, the SONREB (SONic and REBound) method.