| Summary: | Cracks with water leakage have been found in an underground concrete structure, and they have been repaired by injecting waterstop agents and applying patch repair materials after V-shaped removal of existing materials. Since recurrence of the problem has been frequently reported after the repair, test construction has been made by using more proper repair materials. However, an underground structure surrounded by earth is accessible only from the inside for inspection. The authors adopted the surface wave tomography which enabled single-side access soundness evaluation of internal concrete, without requiring the source and receiving sensors to be placed on the opposing sides of an object. The results confirmed the effectiveness of the repair, with the velocity structure found to have improved from that before the repair. It was also found that the velocity has already decreased at some repaired sites, and that they were in agreement with the locations of the recurrence of water leakage detected by the visual inspection. Detection of recurrence of water leakage is important because the water ingress from the surrounding ground is one of the factors leading to reduced durability of the underground structure. The findings of this study suggested that the technique would be also useful for subsequent monitoring.
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