Abstract
Spectral Analysis of Surface Wave (SASW) is widely used in nondestructive subsurface profiling for geological sites. The air-coupled SASW is an extension from conventional SASW methods by replacing ground-mounted accelerometers with non-contact microphones, which acquire a leaky surface wave instead of ground vibration. The air-coupled SASW is a good candidate for fast inspection in shallow geological studies. Especially for pavement maintenance, minimum traffic interference might be induced. One issue that restrains SASW from fast inspection is the traditional slow inversion which relies on guess-and-check iteration techniques including a forward analysis. In this article, a fast inversion analysis algorithm is proposed to estimate the shear velocity profile without performing conventional forward simulation. By investigating the attenuation of particle displacement along penetrating depths, a weighted combination relationship is derived to connect the dispersion curve with the shear velocity profile directly. Using this relationship, the shear velocity profile could be estimated from a given/measured dispersion curve. The proposed procedure allows the surface wave-based method to be fully automatic and even operated in real-time for geological site and pavement assessment. The method is verified by the forward analysis with stiffness matrix method. It is also proved by comparing with other published results using various inversion methods.
Highlights
Many methods are being developed and utilized for the subsurface sensing, including Impact Echo (IE), Impulse Response (IR), Ground Penetrating Radar (GPR), Chain-Drag, and Spectral Analysis of Surface Waves (SASW)
Once the dispersion curve is obtained from the test data, the layer profile, and shear velocities can be estimated by inversion algorithms
The air-coupled SASW is a promising extension for fast non-contact inspection
Summary
Many methods are being developed and utilized for the subsurface sensing, including Impact Echo (IE), Impulse Response (IR), Ground Penetrating Radar (GPR), Chain-Drag, and Spectral Analysis of Surface Waves (SASW). Since first proposed in 1980s [6,7], the SASW has been widely applied in the geological field tests to estimate the underground soil profile without coring or opening the ground [8] It utilizes the dispersion features of the surface wave that propagates horizontally in the soil when it is subject to an impact load. Once the dispersion curve is obtained from the test data, the layer profile, and shear velocities can be estimated by inversion algorithms. Global search algorithm was another effort to minimize the difference between the measured shear velocity spectrum and that calculated from the theoretical layer model, including the field setup geometry [22] This inversion brings new solutions but still somewhat suffers long-term iteration for acceptable accuracy. The accuracy of this method is verified by stiffness matrix method and by comparing the estimated shear velocity profiles with the results from other published methods
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