Road And Soil Dynamic Characterization From Surface Measurements
Creators: name: Iodice, Michele
Publisher: name: Zenodo
Year: 2017
Subjects: NDT
non-destructive testin
soils
asphalt
dispersion curve
frequency-wavenumber
crack detection

description: The increased demand for non-destructive evaluation of the shear wave profiling, condition<br>
monitoring and performance assessment of soils and roads in a dynamic state has made seismic<br>
methods the most desirable and effective non-destructive techniques. Surface wave methods have<br>
gained popularity over the last decades since they monitor the propagation of the surface wave with<br>
non-invasive transducers working from the surface. Nonetheless, their use is restricted by resolution<br>
problems and their ability to assess the actual dispersive behaviour of Rayleigh wave. Nondestructive,<br>
in-situ methods for characterizing existing infrastructures require the ability to detect<br>
structural damage and features such as cracking and discontinuities. The proper assessment of the<br>
location and of the extension of such discontinuities is crucial for the determination of the level of<br>
deterioration of an infrastructure and for planning the maintenance interventions. Damage in a<br>
pavement structure is usually initiated in the asphalt layers, making the Rayleigh wave ideally suited<br>
for the detection of shallow surface defects. Nonetheless, the practical application of crack detection<br>
methods in asphalt is hampered due to the heterogeneous and dispersive nature of the material tested.<br>
This thesis describes new signal processing methods and the novel application of existing methods<br>
to tackle the problems that hinder the non-destructive surface wave methods.<br>
The spectral convolution method proposed in this thesis, based on the simultaneous exploitation of<br>
the vertical and the horizontal components of a seismic event, improved the resolution and the overall<br>
accuracy of the spectral image in the frequency-wavenumber (f-k) domain. Hence, it led to more<br>
accurate seismic inversion by reducing the amount of uncertainty coming from a seismic survey.<br>
This research investigated the use of this new proposed method in soils and asphalts for the measurement of surface wave dispersion through conceptual analysis and numerical investigation<br>
alongside experimental investigation on soil and asphalt.<br>
The application of spectral wave methods and the transformation of the wavefield into the frequencywavenumber<br>
domain allowed the identification of the position and the extension of vertical defects.<br>
The joint use of the Multichannel Analysis of Surface Waves and the Multiple Impact of Surface<br>
Waves methods in numerical and experimental investigations presented in this thesis proved to be<br>
effective for crack detection and sizing. Moreover, the space-normalised seismogram helped in the<br>
interpretation of f-k spectra for cracks detection.<br>
Here, the wave decomposition method for crack interrogation consisted of a signal processing<br>
algorithm capable of computing the direct and reflected waves’ amplitudes and phase angles from<br>
the signals of a deployment of sensors. It solved linear systems with a number of measurements much<br>
bigger than the number of unknowns. It tackled the measurement errors naturally present in<br>
experimental data by finding a least square approximate solution with the help of the pseudo-inverse<br>
matrix for overdetermined systems. The results coming from numerical simulations and experimental<br>
investigations showed the effectiveness of the wave decomposition method for the assessment of the<br>
location and of the depth of surface-breaking cracks in the half-space and in layered systems.<br>
Contrary to other techniques, it was able to cope with the heterogeneities and the dispersive nature<br>
of layered system, thus making possible to detect and assess the depth of surface-breaking cracks in<br>
roads.