Application of Impact Imaging Method on Nondestructive Detection of Void Defects in Sandwich-Structured Immersed Tunnel

Figure 9

Spectrogram of the response waveform of each measuring point. (a) a₁ dense region (5 cm from T-stiffener), (b) a₂ dense region (10 cm from T-stiffener), (c) a₁ dense region (5 cm from T-stiffener), and (d) a₂ dense region (10 cm from T-stiffener).

(a)

(b)

(c)

(d)