Abstract
Abstract
Incomplete grouting backfill behind tunnel segment linings can create hidden cavities that are difficult to detect from the surface. The objective of this study is to estimate the size and shape of cavities beneath tunnel segment linings using ground penetrating radar (GPR) and acoustic sensing in laboratory tests. The tunnel segment lining and backfilling material are simulated using reinforced and plain concrete plates. Square and circular cavities with lengths (diameters) of 30 cm and 60 cm, respectively, are prepared on plain concrete plate. The reinforced concrete plate is placed on the plain concrete plate and the two plates are attached with mortar. GPR and microphone surveys are performed above the reinforced concrete plate on the survey lines with and without cavities. The results show that the GPR effectively detected the presence of cavities, but the estimation of cavity sizes was relatively inaccurate due to the influence of rebars. In contrast, the microphone was less affected by the rebars, and it enabled more accurate detection and estimation of cavity dimensions. This study confirms that microphones may be used efficiently for detecting cavities beneath the tunnel segment linings.