318
Y. Yang et al.
Fig. 26.6 The positional
relationship between the
gallery and the surface of the
levee
inspection gallery, the sensors had to be arranged to be rising up with an interval
of 1.5 m. Figure 26.6 shows the positional relationship between the measurement
points of the dam surface and the inspection gallery. The elevation of the bottom
floor of the inspection gallery is 128.5 m, and the elevation of the crack on the dam
surface is 145 m.
Various coordinate such as the coordinates of measurement points were derived
from simple measurement and drawings and detailed measurement of coordinates has
not been performed. The propagation distance of the elastic wave in this measurement
was about 25–30 m.
26.3.2 Surface Wave Tomography
In the elastic wave tomography, it is necessary that the elastic wave path passes
through the structure. However, for some situations such as tunnel lining concrete,
bridge slab and retaining wall, the sensor arrangement is limited to the surface and
the elastic wave tomography will be difficult to conduct. Meanwhile, the Rayleigh
wave, is a kind of surface wave, propagates near the surface of the medium. Also,
the Rayleigh wave carries more energy and has lower attenuation than P wave and
S wave. Most importantly, the propagation depth of the Rayleigh wave depends
on the wavelength or frequency. With all of these characteristics, Rayleigh wave is
regarded as a promising tool of the damage evaluation near the concrete surface. In
this research, the phase velocity of Rayleigh wave was obtained and the tomography
analysis same as the elastic wave tomography was conducted.
The measurement equipment such as wide band recorder and sensor were same
as those used in the elastic wave tomography. The sampling rate was 50 kHz. And
Y. Yang et al.
Fig. 26.6 The positional
relationship between the
gallery and the surface of the
levee
inspection gallery, the sensors had to be arranged to be rising up with an interval
of 1.5 m. Figure 26.6 shows the positional relationship between the measurement
points of the dam surface and the inspection gallery. The elevation of the bottom
floor of the inspection gallery is 128.5 m, and the elevation of the crack on the dam
surface is 145 m.
Various coordinate such as the coordinates of measurement points were derived
from simple measurement and drawings and detailed measurement of coordinates has
not been performed. The propagation distance of the elastic wave in this measurement
was about 25–30 m.
26.3.2 Surface Wave Tomography
In the elastic wave tomography, it is necessary that the elastic wave path passes
through the structure. However, for some situations such as tunnel lining concrete,
bridge slab and retaining wall, the sensor arrangement is limited to the surface and
the elastic wave tomography will be difficult to conduct. Meanwhile, the Rayleigh
wave, is a kind of surface wave, propagates near the surface of the medium. Also,
the Rayleigh wave carries more energy and has lower attenuation than P wave and
S wave. Most importantly, the propagation depth of the Rayleigh wave depends
on the wavelength or frequency. With all of these characteristics, Rayleigh wave is
regarded as a promising tool of the damage evaluation near the concrete surface. In
this research, the phase velocity of Rayleigh wave was obtained and the tomography
analysis same as the elastic wave tomography was conducted.
The measurement equipment such as wide band recorder and sensor were same
as those used in the elastic wave tomography. The sampling rate was 50 kHz. And