Nondestructive testing of prestressed ground anchors using ultrasonics: theory, simulation, and experiments

Prestressed ground anchors have been widely used in numerous slopes to prevent slope failure. However, the inevitable loss of prestress can affect the long-term operational safety of slopes in the field of prevention and control engineering. This study analysed the deterioration of the external anchor head and its main causes based on a field investigation, and a theoretical model for the non-destructive testing (NDT) of prestressed slope anchors using ultrasonics was derived. Subsequently, the stress and displacement distribution characteristics of the anchor head were analysed by numerical simulation. Two ultrasonic sensors (2.5 MHz and 5.0 MHz) were employed to test the prestress of the anchor, and a relationship between the energy and prestress was established. The results showed that the prestress can be determined by analysing the reflection waves, the energy of which decreased nonlinearly with increasing load, and the energy – prestress relationship could be well fitted using an exponential function. The 2.5 MHz ultrasonic sensor outperformed the 5.0 MHz ultrasonic sensor, and the third reflection wave (RW3) exhibited the highest stability and best fitting, making it suitable for establishing the relationship between the energy and prestress of the ground anchor. This study provides references for the NDT of prestressed ground anchors.