Study on applicability of noncontact acoustic inspection method to shotcrete with rough surface

Sugimoto, Tsuneyoshi; Toin University of Yokohama; Japan

Sugimoto, K.; Toin University of Yokohama; Japan
Sugimoto, T.; Toin University of Yokohama; Japan

ID: ECNDT-0561-2018
Download: PDF
Session: Civil Infrastructure - AE
Room: J1
Date: 2018-06-12
Time: 13:50 - 14:10

By using acoustic irradiation induced vibration and laser Doppler vibrometer (LDV), noncontact acoustic inspection method for concrete non-destructive measurement has been studied. By using a long range acoustic device (LRAD) as a sound source and a scanning vibrometer (SLDV; Scanning Laser Doppler Vibrometer) as a LDV, it has already been demonstrated that non-destructive exploration can be performed even if it is separated from concrete specimens or actual structures by 30 m or more.

On the other hand, in shotcrete inside huge cavities of underground power plants, cracking and small surface peeling due to drilling and secular change have been confirmed. For safety, there are cases where periodic hammering inspections using ceiling cranes are performed for ceiling cracks, but because it is difficult to hit directly without a scaffolding etc., development of an inspection method that can be carried out over a long distance without contact is required. However, the surface condition of shotcrete in the underground huge cavities differs greatly from general concrete specimens and actual concrete structures which have been used conventionally, and the surface unevenness is considerably large. In other words, the possibility that the measurement might not be stabilized due to the influence such as the excitation force by sound wave and the laser return light being unstable was considered. In order to investigate the applicability of noncontact acoustic inspection method for defect detection of shotcrete, a verification experiment was conducted on the wall of the huge cavity inside the existing underground power station.

The defect judgment result by the noncontact acoustic inspection method was almost consistent with the defect judgment result by the existing hammering inspections at any place. Therefore, we have confirmed the applicability of this method to shotcrete, which has the feature that noncontact measurement from a long distance is possible.