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Near Surface Site Characterization U...

Nguyen, Trung Dung.

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Near Surface Site Characterization Using 3-D Full Waveform Tomography.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Near Surface Site Characterization Using 3-D Full Waveform Tomography./
作者:	Nguyen, Trung Dung.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	123 p.
附註:	Source: Dissertation Abstracts International, Volume: 80-03(E), Section: B.
Contained By:	Dissertation Abstracts International80-03B(E).
標題:	Civil engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10745153
ISBN:	9780438507555

Near Surface Site Characterization Using 3-D Full Waveform Tomography.
Nguyen, Trung Dung.

Near Surface Site Characterization Using 3-D Full Waveform Tomography. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 123 p.

Source: Dissertation Abstracts International, Volume: 80-03(E), Section: B.

Thesis (Ph.D.)--Clarkson University, 2018.

Unanticipated site conditions such as highly variable soil/rock layers with embedded low-velocity anomalies (soft soils or voids) cause significant problems during and after construction of foundations. Knowledge of the anomalies is crucial, as the anomalies can cause structural damage or collapse that can result in significant property damage and occasional loss of life. Site characterization methods using seismic waves, which can characterize large volumes of material, are often used to overcome the limitations of the traditional invasive methods. Seismic surface wave fields could be used to identify and quantify embedded anomalies and characterize variable soil/rock layers, as the propagation properties of seismic waves are modulated by the anomalies and layer interfaces. These seismic methods require measurement of wave fields and an inversion algorithm to invert the measured data for material properties (wave velocities). The inversion is to find earth models that best explain the seismic observations. The earth model is described by physical parameters that characterize properties of soil/rock layers such as compression and shear wave velocities (P-wave and S-wave velocities), density, etc.

ISBN: 9780438507555Subjects--Topical Terms:

860360
Civil engineering.

Near Surface Site Characterization Using 3-D Full Waveform Tomography.
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245 1 0 $a Near Surface Site Characterization Using 3-D Full Waveform Tomography.
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300 $a 123 p.
500 $a Source: Dissertation Abstracts International, Volume: 80-03(E), Section: B.
500 $a Adviser: Khiem Tran.
502 $a Thesis (Ph.D.)--Clarkson University, 2018.
520 $a Unanticipated site conditions such as highly variable soil/rock layers with embedded low-velocity anomalies (soft soils or voids) cause significant problems during and after construction of foundations. Knowledge of the anomalies is crucial, as the anomalies can cause structural damage or collapse that can result in significant property damage and occasional loss of life. Site characterization methods using seismic waves, which can characterize large volumes of material, are often used to overcome the limitations of the traditional invasive methods. Seismic surface wave fields could be used to identify and quantify embedded anomalies and characterize variable soil/rock layers, as the propagation properties of seismic waves are modulated by the anomalies and layer interfaces. These seismic methods require measurement of wave fields and an inversion algorithm to invert the measured data for material properties (wave velocities). The inversion is to find earth models that best explain the seismic observations. The earth model is described by physical parameters that characterize properties of soil/rock layers such as compression and shear wave velocities (P-wave and S-wave velocities), density, etc.
520 $a Existing seismic methods are often used for geotechnical site characterization to assess spatial variation and material properties. They include 1-D surface wave, 2-D refraction tomography, and 2-D full waveform tomography methods. The surface wave method such as multichannel analysis of surface waves (MASW) method uses dispersive characteristic of Rayleigh waves to determine 1-D S-wave velocity (Vs) profiles. This method tends to average Vs values over considerable volumes of material, and it is not very sensitive to thin embedded low-velocity layers. Refraction tomography uses the first-arrival times to determine P-wave velocity (Vp) profiles. As the first-arrival signals tend to propagate through high-velocity layers, embedded low-velocity layers are not well characterized. The 2-D full waveform tomography methods have been developed and successfully used for geotechnical site characterization. However, due to 3-D effects, these 2-D methods tend to average material properties out of testing planes, and thus produce less accurate results than invasive tests (point by point).
520 $a To overcome limitations of the existing seismic methods, this study develops a new three-dimensional full waveform inversion (3-D FWI) method using seismic wave fields for geotechnical site characterization at high-resolution (meter pixel). The seismic wave fields are acquired from non-destructive testing (NDT) using sensors (receivers) and sources located in uniform 2-D grids on the ground surface, and then inverted for extraction of 3-D subsurface wave velocity structures. The analysis approach is based on a solution of the 3-D elastic wave equations and cross-adjoint gradient method. The staggered-grid finite-difference technique is used to solve the wave equations, together with implementation of the perfectly matched layer condition for boundary truncation. This numerical modelling has the ability to generate all possible wave propagation modes of seismic wave fields (body waves and Rayleigh (surface) waves) in 3-D domain, which is then compared with measured data to infer complex subsurface properties. The gradient is calculated from the forward and backward wave fields. Reversed-in-time displacement residuals are induced as multiple sources at all receiver locations for the backward wavefield. The gradient preconditioning and the optimal step lengths are also implemented to reduce computer time and eliminate inversion artifacts.
520 $a The capability of the 3-D FWI method is tested on both synthetic and real experimental data sets. The inversion results from synthetic data show the ability of detecting reverse models, which are hardly characterized by traditional seismic methods that use only dispersion property of Rayleigh waves or travel times. The embedded anomalies are also detected from synthetic study, as signals reflected and refracted from the anomalies at different angles are utilized for analyses. Furthermore, off-line anomalies, which cannot be detected by a 2-D analysis because of the 3-D effect, can be characterized by the 3-D analysis, as the 3-D analysis completely handles the effect problem. Field experimental data were collected using 96 receivers and a propelled energy generator (PEG) to induce seismic wave energy. The field data result shows that the waveform analysis is able to delineate variable subsurface soil/rock layers. The seismic inversion results are generally consistent with invasive standard penetration test (SPT) N-values, including identification of low-velocity zones.
590 $a School code: 0049.
650 4 $a Civil engineering. $3 860360
650 4 $a Geotechnology. $3 1018558
650 4 $a Geophysics. $3 535228
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710 2 $a Clarkson University. $b Civil & Environmental Engineering. $3 3426948
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