[Truncated abstract] Seismic tomography has been extensively used in geophysics for different purposes such as geological mapping and prospecting for oil and gas. In geophysics, ultrasound or electromagnetic waves are normally used to provide the tomographic information. In the geotechnical area, seismic tomography is emerging as a promising technique that can be used to determine the spatial variability of shear wave velocities and hence the small strain stiffness of geomaterials. Although some studies have been undertaken to incorporate seismic measurement into centrifuge modelling, there has been to date no attempt to build a complete seismic tomography facility with high resolution for use in a geotechnical centrifuge. Such a powerful facility can help in better understanding of soil behaviour by providing a complete picture of the spatial variation of the soil property of concern. The main aim of this study was to develop a high-resolution seismic tomography (ST) system for the beam centrifuge at the University of Western Australia (UWA) by which the shear wave velocity and hence maximum shear modulus could be determined anywhere in the centrifuge model. ... This limitation was the requirement to use an a priori model. The exact solutions in the different examples presented in this chapter were known, and they were used as a priori models into the inversion process. However, in practice the exact solution is unknown, and the aim of the tomographic inversion is to obtain a solution that best describes the measured data. Carrying out inversion without using an a priori model can yield an output model that hints at the nature of the model. This output can then be used as the starting point in an iterative process, in which the output from one step is used as an a priori model for reinverting the original data in a subsequent step. In this case, this process slightly improved the output tomogram and decreased the value of root mean squares of travel time residuals (Rrms). An alternative inversion strategy was proposed based on the results obtained in this study. It involves using a searching algorithm. A searching process can be carried out based on the output from the first iteration (without using an a priori model). The search can involve varying the parameters that describe buried anomalies, such as the size of the anomaly, the velocity value in the anomaly, and the location of the anomaly. The aim is to search for the combination of anomaly parameters that minimises the resulting error parameters (mainly Rrmx, but also the average error and the standard deviation of the error). For more subtle cases, such as the velocity model under a footing, where inversion without using an a priori model did not recover the input model, a searching algorithm involving applying perturbations to the exact Boussinesq model can be performed. Not only can the searching procedure involve adding perturbation to the velocity values in the Boussinesq model, but it can also add perturbation to the shape of the velocity distribution below the footing. The searching process can continue until a model that fits the data with a minimum error is found, i.e., minimising Rrms.

The seismic cone penetration test (SCPTu) is the most efficient means for geotechnical site characterization and the evaluation of seismic ground hazards. In this thesis, software systems including ShearPro, ClusterPro, and InSituData, are developed to automate post processing of these SCPTu data. ShearPro is developed to automate the post-processing of the shear wave signals. ClusterPro uses the proposed three-dimensional cluster analysis approach for soil stratification. InSituData facilitates the post processing of penetration data for seismic ground hazards analysis. A new three-dimensional soil classification chart is also proposed in this thesis to help discern soil layers that may be subject to seismic ground hazards, such as loose liquefied sands and silty sands. These methods are then applied to SCPTu data collected at previously-identifed paleoliquefaction sites located in the New Madrid Seismic Zone (NMSZ). For liquefaction evaluation, the cyclic stress ratio (CSR) is computed using site response analysis by DeepSoil and a measured profile of shear waves derived from the 30-m SCPTU soundings and deep suspension loggings in AR and TN. The natural resistance of the soil to liquefaction, termed the cyclic resistance ratios (CRRs), is evaluated based on both deterministic procedures and probabilistic procedures. Based on liquefaction evaluation results at selected paleoliquefaction sites, regional CRR criteria for liquefaction are developed for the NMSZ. As even the latest major earthquakes in NMSZ occurred nearly 200 years ago, aging effects might be an important factor to consider in utilizing the liquefaction criteria to assess the seismic parameters associated with the previous earthquakes. The aging effects in the NMSZ were investigated through large scale blast-induced liquefaction tests conducted in the NMSZ. Then a procedure to estimate seismic parameters associated with previous earthquakes is proposed. It utilizes both the liquefaction criteria based on SCPTu tests and the empirical attenuation relations developed for the corresponding regions. The approach is validated through data evaluation related to the 1989 Loma Prieta earthquakes in California and then applied to previous historic earthquakes in the NMSZ.

Nonlinear site response analyses are generally preferred over equivalent linear analyses for soft soil sites subjected to high-intensity input ground motions. However, both nonlinear and equivalent linear analyses often result in large induced shear strains (3-10%) at soft sites, and these large strains may generate unusual characteristics in the predicted surface ground motions. One source of the overestimated shear strains may be attributed to unrealistically low shear strengths implied by commonly used modulus reduction curves. Therefore, modulus reduction and damping curves can be modified at shear strains greater than 0.1% to provide a more realistic soil model for site response. However, even after these modifications, nonlinear and equivalent linear site response analyses still may generate unusual surface acceleration time histories and Fourier amplitude spectra at soft soil sites when subjected to high-intensity input ground motions. As part of this work, equivalent linear and nonlinear 1D site response analyses for the well-known Treasure Island site demonstrate the challenges associated with accurately modeling large shear strains, and subsequent surface response, at soft soil sites. Accounting for the uncertainties associated with the shear wave velocity profile is an important part of a properly executed site response analyses. Surface wave data from Grenoble, France and Mirandola, Italy have been used to determine shear wave velocity (Vs) profiles from inversion of surface wave data. Furthermore, Vs profiles from inversion have been used to determine boundary, median and statistically-based randomly generated profiles. The theoretical dispersion curves from the inversion analyses as well as the boundary, median and randomly generated Vs profiles are compared with experimentally measured surface wave data. It is found that the median theoretical dispersion curve provides a satisfactory fit to the experimental data, but the boundary type theoretical dispersion curves do not. Randomly generated profiles result in some theoretical dispersion curves that fit the experimental data, and many that do not. Site response analyses revealed that the greater variability in the response spectra and amplification factors were determined from the randomly generated Vs profiles than the inversion or boundary Vs profiles.

During the past two decades, University of Kentucky researchers have been acquiring seismic refraction/reflection data, as well as seismic downhole data, for characterizing the seismic velocity models of the soil/sediment overburden in the central United States. The dataset includes densely spaced measurements for urban microzonation studies and coarsely spaced measurements for regional assessments. The 519 measurements and their derivative products often were not in an organized electronic form, however, limiting their accessibility for use by other researchers. In order to make these data more accessible, this project constructed a database using the ArcGIS 9.1 software. The data have been formatted and integrated into a system serving a wider array of users. The seismic shear-wave velocity models collected at various locations are archived with corresponding x-, y-, and z-coordinate information. Flexibility has been included to allow input of additional data in the future (e.g., seismograms, strong ground-motion parameters and time histories, weak-motion waveform data, etc.). Using the completed database, maps of the region showing derivative dynamic site period (DSP) and weighted shear-wave velocity of the upper 30 m of soil (V30) were created using the ArcGIS 9.1 Geostatistical Analyst extension for examination of the distribution of pertinent dynamic properties for seismic hazard assessments. Both geostatistical and deterministic techniques were employed. Interpolation of V30 data yielded inaccurate predictions because of the high lateral variation in soil layer lithology in the Jackson Purchase Region. As a result of the relatively uniform distribution of depths to bedrock, the predictions of DSP values suggested a high degree of accuracy.

Esta dissertação apresenta o método de análise espectral de ondas superficiais (SASW) para a obtenção das variações do módulo cisalhante (Gmáx) com a profundidade, no domínio das deformações muito pequenas (abaixo de 0,001%). O SASW é um método sísmico in situ, não destrutivo, baseado na geração e detecção de ondas Rayleigh e na natureza dispersiva desta onda. Pela aplicação de um impacto na superfície do solo e detecção da onda em vários pontos, através de dois receptores, é construída uma curva de dispersão (velocidade de fase versus comprimento de onda). Esta curva de dispersão é, então, invertida. A inversão é um processo analítico para a reconstrução do perfil de velocidade de onda de cisalhamento (VS), partindo-se da curva de dispersão experimental de campo. O módulo de cisalhamento máximo de cada camada é facilmente obtido a partir do perfil de VS. No conteúdo teórico da dissertação discutem-se propriedades dinâmicas dos solos e descrevem-se as equações que dominam a propagação das ondas elásticas, tanto em meios homogêneos como em meios estratificados. A metodologia desenvolvida para a obtenção das curvas de dispersão, através da realização de ensaios SASW, apresenta os resultados obtidos em ensaios realizados na Cidade Universitária em São Paulo, sendo esses resultados comparados com estimativas feitas a partir de correlações baseadas em ensaios SPT existentes. Essas comparações permitem concluir que a metodologia SASW é uma boa alternativa para a determinação do perfil de rigidez (Gmáx) do solo, concordando com o nível de deformação envolvido nos ensaios. São desenvolvidos estudos de sensibilidade do método para verificar a influência na mudança dos parâmetros assumidos (peso específico, coeficiente de Poisson e espessuras das camadas) no processo de redução de dados (inversão) sobre o perfil final de VS, concluindo-se que o parâmetro que apresenta maior influência é o coeficiente de Poisson. / This dissertation presents the spectral-analysis-of-surface-waves (SASW) method as a tool for obtaining the variations in the modulus shear (Gmax) with depth in the field of very small strains (below 0,001%). The SASW method is a nondestructive in situ seismic method, based on the generation and measurement of Rayleigh wave and on its dispersive characteristic nature. Throughout the implementation of an impact on the soil surface and the detection of the wave at various points by two receptors a dispersion curve is constructed (phase velocity versus wave-length). This dispersion curve is then inverted. Inversion is an analytical process for reconstructing the shear wave velocity profile from the experimental field. The shear modulus of each layer is readily obtained from the shear wave velocity profile. The theoretical content of the dissertation presents dynamic properties of the soils and is described in the equations that dominate the propagation of elastic waves, both in homogeneous media and in stratified media. The methodology developed to obtain the dispersion curves through the implementation of SASW test is defined, and results from tests carried out at the University Campus in São Paulo are presented and compared with values obtained from correlations based on SPT tests. These comparisons indicate that the SASW method is a good alternative to determine the profile of stiffness (Gmax) of the soil, agreeing with the level of deformation involved in the tests. Studies on the methods sensitivity are developed to verify the influence on the changing of the parameters given (natural unit weight, Poisson coefficient and thickness of layers) in reduction of data (inversion) on the final profile of VS. The conclusion is that the Poisson coefficient is the parameter with greater influence.

Thesis advisor: John E. Ebel / Thesis advisor: Alan L. Kafka / As the best seismic indicator of shear modulus, shear-wave velocity is an important property in engineering problems in near-surface site characterization. Several surface-wave methods have been developed to obtain the subsurface shear-wave velocity structure. This thesis compared three surface-wave methods, Spectral Analysis of Surface Waves (SASW) (Nazarian et al., 1983), Multichannel Analysis of Surface Waves (MASW) (Park et al., 1999), and Refraction Microtremor (ReMi) (Louie, 2001), to determine which method gives the best estimation of the 1-D shear-wave velocity profile of near-surface soils. We collected seismic data at three sites in the greater Boston area where there are direct measurements of shear-wave velocities for comparison. The three methods were compared in terms of accuracy and precision. Overall, the MASW and the ReMi methods have comparable quality of accuracy, whereas the SASW method is the least accurate method with the highest percentage differences with direct measurements. The MASW method is the most precise method among the three methods with the smallest standard deviations. In general, the MASW method is concluded to be the best surface-wave method in determining the shear-wave velocities of the subsurface structure in the greater Boston area.

The development of a site-specific seismic hazard curve for a soil site requires the incorporation of site effects into the hazard calculation through the use of a site-specific amplification function. This study investigates the effect on the resulting soil hazard curves of different approaches to compute the site-specific amplification function. Amplification functions and their standard deviations can be developed using equivalent linear site response analyses. This study investigates the amplification function predictions of one-dimensional (1D) and two-dimensional (2D) site response analyses. For 1D analysis, one set of analyses are performed using time series (TS) input motions while a second set is performed using random vibration theory (RVT). One-dimensional site response analyses are performed for a shallow and a deep soil site and the results are compared for seismic hazard predictions. The influence of spatial variability introduced through randomization of site shear wave velocity (V[subscript S]) is also investigated. Shear wave velocity profile randomization does not significantly change the predicted amplification functions, except for the RVT analysis near the site period. At these periods, (V[subscript S]) randomization reduces the amplification function predicted by RVT making it more similar to the TS analysis prediction. The surface hazard at a site is dependent on the median amplification factor and its associated standard deviation. Spatial variability and uncertainties in soil properties across a site are often taken into account by modeling multiple 1D profiles in 1D site response analyses. However, this approach assumes that analyzing multiple 1D profiles captures accurately the effects of the true multi-dimensional spatial variability of the soil properties. This study investigates the results of two-dimensional (2D) site response analyses that incorporate spatial variability in the (V[subscript S]) profile through Monte Carlo simulation. Two-dimensional site response analyses are performed for 2D random fields generated with various statistical parameters (i.e. vertical and horizontal correlation distances) to investigate the effect of different levels of spatial variability on surface response across a region of interest (ROI). Two-dimensional site response analyses are performed for a shallow site. Results indicate that horizontal correlation distance has more influence on the analyses results than the vertical correlation distance. As the horizontal correlation distance increases, the median surface response spectrum across the ROI decreases. This reduction in median surface response is more pronounced around the site period. The influence of the vertical correlation distance is more pronounced when the horizontal correlation distance is large. As the vertical correlation distance increases, the median surface response spectrum across the ROI increases, which is more pronounced around the period of the motion. The predictions of 1D and 2D site response analyses modeling the (V[subscript S]) variability are compared. 1D analyses are performed on separately generated 1D (V[subscript S]) profiles (infinite horizontal correlation) and on the (V[subscript S]) profiles across the ROI of each 2D (V[subscript S]) field realization generated for 2D analysis (finite horizontal correlation). The results indicate that both sets of 1D analyses predict lower median response than 2D analyses. The 1D analyses with finite horizontal correlation display comparable levels of variability in the site response, however 1D analyses with infinite horizontal correlation display higher variability. / text

The behavior of unsaturated soils depends heavily on material properties and soil conditions. In Geotechnical Engineering, compacted soils are frequently used as fill material, and quality control is vital to the construction process. There are few methods available to estimate the parameters associated with unsaturated soils based on field measurements, and a relationship between these factors could reduce testing time and lower construction costs. Undrained triaxial tests were performed on four clays representing a range of material properties in an effort to reach the maximum dry density, which provides the highest bearing capacity. Each clay was compacted at optimum moisture content, as well as wet and dry of optimum. Measurements were taken using the GeoGauge and shear wave velocities. An empirical approach was used to estimate the effect of a density gradient on soil suction. A relationship between the normal stress and matric suction produced a strong trend when plotted against a function of stiffness and the void ratio, which represents a density gradient. Another relationship between the GeoGauge and shear wave stiffness measurements was found, but no relationship with the material properties of the samples was observed, indicating that more in-depth research is needed to find a stronger relationship.

Natural geomaterials exhibit a wide range in size, physical properties, chemical properties, and mechanical behaviors. Soils that are composed of mixtures of particles with different physical and chemical properties pose a challenge to characterization and quantification of the engineering properties. This study examined the behavior of particulate mixtures composed of differently sized silica particles, mixtures composed of aluminosilicate and organic carbon particles, and mixtures composed of particles with approximately three orders of magnitude difference in particle size. This experimental investigation used elastic, electromagnetic, and thermal waves to characterize and to quantify the small to intermediate strain behavior of the mixtures. The mechanical property of stiffness of mixed materials (e.g. binary mixtures of silica particles and fly ashes with various carbon and biomass contents) was evaluated through the stiffness of active grain contacts, and the stiffness of particles which carry applied load, using the physical concepts of intergranular void ratio and interfine void ratio. Additionally, the change in both contact mode/stiffness and electrical property due to the presence of nano-sized particles (i.e., iron oxides) on the surface of soil grains was evaluated according to applied stress, packing density, iron coating density, and substrate sand particle size. Finally, the biomass fraction and total organic carbon content of mixtures was used to quantify the electrical and thermal conductivities when particulate organic was mixed with aluminosilicate particles.

Hydrate-bearing sediments may contribute to the availability of energy resources, affect climate change, or cause seafloor instability. The comprehensive study of hydrate-bearing sediments documented in this manuscript includes physicochemical aspects of hydrate nucleation near mineral surfaces, the validity of THF as a substitute guest molecule for the study of hydrate-bearing sediments, and the effects of hydrate formation on the electromagnetic and the mechanical properties of various soils with a wide range of specific surface. Natural marine sediments are included as part of this investigation to explore the effects of inherent fabric, salts, organic matter, and stress history on the geophysical properties of hydrate-bearing sediments. Experiments are designed to reproduce the state of effective stress in the field at the time of hydrate formation. A comprehensive set of instruments is deployed in this study, and the unprecedented development of electrical resistivity tomography for the study of hydrate formation and dissociation is also documented in detail. Results from this research have important implications for geophysical field characterization and monitoring processes such as production.