Evaluation of the Backfill Condition behind the Steel Plate Lining using Impact-Echo

초록

Voids behind the tunnel lining can lead to ground settlement and impose uneven loads on the lining, thereby compromising tunnel stability. To mitigate such risks, backfill grouting is applied, and non-destructive testing(NDT) methods are essential to verify whether the backfill grouting has been properly injected. In a recent project at the OO Tunnel, steel plate lining was additionally installed inside the segmental lining to enhance stability during excavation in soft ground. The backfill grouting was also applied behind the steel plate lining, and its condition must be evaluated using appropriate non-destructive testing(NDT) methods. However, the commonly used ground-penetrating radar(GPR) method, based on electromagnetic wave propagation, has inherent limitations in evaluating conditions behind steel materials. To address this limitation, this study employs the elastic wave-based Impact-Echo(IE) method to evaluate the condition behind the steel plate lining. To establish evaluation criteria for the condition of backfill grouting, reference tests were conducted under known fill and void conditions, and corresponding signal characteristics were analyzed in the time domain, frequency domain, and time?frequency domain. Based on these reference criteria, field tests were carried out at tunnel sites, and the IE method successfully evaluated the backfill conditions behind the steel plate lining.