Monofrequency in situ damping measurements in Ottawa area soft soils

Crow, Heather; Hunter, James A.; Motazedian, Dariush

doi:10.1016/j.soildyn.2011.07.002

Cited by 24 publications

(21 citation statements)

References 21 publications

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“…However, the clay fabric can influence the degree of dependency; such that the loading frequency has minimal effect on the G max of the naturally-cemented clays with less viscous characteristics, compared to the de-structured clays with direct contacts between clay particles (Soga 1994). This is consistent with the findings of Crow et al (2011) from field geophysical experiments regarding the frequency-independent trend of the low-amplitude shear wave velocity in Leda clay. The only measurement of G max for Leda clay from an RC test was reported to be around 28 Mpa by Rasmussen (2012).…”

Section: Properties Of Leda Clay From Laboratory Testssupporting

confidence: 92%

“…3. The in situ small-strain damping of Leda clay was determined to be fairly frequency-independent and varies in a range of 0.1-0.4 % (Crow et al 2011). Thus, in order to simulate this level of damping within the dominant frequency range of the system (0.25-10 Hz), two target frequencies f 1 ¼ 0:1 Hz and f 2 ¼ 50 Hz with the corresponding damping ratios f 1 ¼ f 2 ¼ 2% were used in the Rayleigh damping formulation.…”

Section: Viscous Dampingmentioning

confidence: 99%

“…Rasmussen (2012) also performed a number of cyclic DSS (DCSS) tests on undisturbed Leda clay samples to characterize cyclic resistance and to develop soil stiffness degradation (G/G max ) and hysteretic damping (D) curves for Leda clay in the large shear strain Figure 2 depicts the G/G max and damping curves with the level of cyclic shear strain, from the described cyclic tests which were adopted herein for site response analysis. Following the outcomes of in situ geophysical testing by Crow et al (2011) in intervals of massive Leda clay, the very low-strain damping ratio (D min ) was adjusted to 0.4 %. Moreover, they concluded that Leda clay exhibits fairly frequency-independent smallstrain stiffness and damping over the frequency range of 10-100 Hz.…”

Section: Properties Of Leda Clay From Laboratory Testsmentioning

confidence: 99%

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Comprehensive nonlinear seismic ground response analysis of sensitive clays: case study—Leda clay in Ottawa, Canada

Torabi

Rayhani

2016

Bull Earthquake Eng

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A series of time domain nonlinear and frequency domain equivalent-linear ground response analysis was conducted for a representative site in Ottawa, Canada. The objective is to provide insight into the performance of different site response analysis approaches in predicting site amplification factors for the soft soil deposit over a wide range of shear strain. The surficial geology of the site is predominantly composed of the sensitive Leda Clay typical of this region in eastern Canada. A combination of results and observations from monotonic and cyclic laboratory tests, as well as field geophysical experiments, was used to calibrate the dynamic properties of the Leda clay, more specifically, the variation of the clay's shear stiffness (G max ) with the in situ stress state (r 0 vc ; OCR). The calibrated relation was then successfully validated through materialspecific site response analysis using the strong motion recordings from the 2010 Val-desBois earthquake and the shear wave velocity profile from borehole data. Comparison of the results with the hazard spectra proposed by NBCC 2010 reveals that the code-based site class E hazard spectra for the Ottawa area can be sufficient for seismic design, except around the natural site period. The results also suggest that the nonlinear analysis using the shear strength-adjusted hyperbola for modulus reduction and best-fitting trend to the laboratorybased damping would provide a reliable estimation of ground motion spectra at the natural site period. The performance of the ground response analysis alternatives for the sensitive clays, over a wide strain range was compared and discussed.

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Section: Properties Of Leda Clay From Laboratory Testssupporting

confidence: 92%

Section: Viscous Dampingmentioning

confidence: 99%

Section: Properties Of Leda Clay From Laboratory Testsmentioning

confidence: 99%

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Comprehensive nonlinear seismic ground response analysis of sensitive clays: case study—Leda clay in Ottawa, Canada

Torabi

Rayhani

2016

Bull Earthquake Eng

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“…Following the outcomes of in-situ geophysical testing by Crow et al (2011) in intervals of massive Leda clay, the very low-strain damping ratio (Dmin) was adjusted to 0.4 %. Moreover, they concluded that Leda clay exhibits fairly frequency-independent small-strain stiffness and damping.…”

Section: Properties Of Leda Clay From Laboratory Testsmentioning

confidence: 99%

A Hybrid Approach for Nonlinear Soil-Structure Interaction Analysis of Pile- Supported Bridges

Torabi¹

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The large-diameter reinforced concrete pile shafts are commonly designed as an economical solution for foundation of highway bridges in soft soils. The substructure method is a widely used technique for seismic SSI analysis of pile-supported bridges due to its remarkable computational efficiency. In the substructure modelling, the complexvalued impedance functions are used to represent the stiffness and energy dissipation characteristics of the soil-pile interaction system. While characteristics of the pile head impedance functions have been decently determined for linear soil-pile interaction, the effects of inelastic interaction on the impedance function still remain unclear. In fact, this study is an attempt to overcome the limitations of linear elastic soil and rigid soil-pile interface bonding assumptions that have been used in substructure analysis. This thesis aims to develop numerical and analytical frameworks to (i) investigate seismic response of a representative bridge superstructure supported by a large-diameter pile shaft under fully coupled inelastic soil-pile-structure interaction, and (ii) compute the equivalent-linear (EL) pile head impedance functions under the controlled dynamic and earthquake loading modes. Hence, a three-dimensional finite element (FE) model of the soil-pile system, as a rigorous direct method of SSI analysis is developed. The pile shaft lateral capacity is designed following to the AASHTO LRFD guidelines. The developed model is verified using data from centrifuge tests. In order to compute EL impedance functions from the continuum FE model, an algebraic solution is derived for the system of dynamic equilibrium equations in substructure analysis. In this frequency-domain solution, the Fourier transform of the force and displacement values obtained from the time-domain ii FE analysis are inserted, while the closed-form solution for the pile head impedance matrix is derived in terms of infinite series. Results of parametric FE analyses indicate that except for the extreme near-fault motions, the residual structural drift and the pile bending moment of the system would hardly exceed the design limits. The computed EL impedances provide insight into the damping evolution and stiffness reduction due to inelastic interaction over a frequency range of interest. As a key conclusion, it is shown that soil and interface inelasticity can drastically alter the impedance values compared to their fully elastic counterpart. iii ACKNOWLEDGEMENTS I would like to express my gratitude to my research advisor, Dr. Mohammad Rayhani, for his support, guidance, motivation and patience throughout the five years of my doctoral study. I would like to thank Professors Ertugrul Taciroglu from University of California, Los Angeles, Siva Sivathayalan and Dariush Motazedian from Carleton University and Julio angel Infante Sedano from university of Ottawa for serving on my dissertation committee and their insightful comments.Heartfelt thanks to my parents and little sister for their unconditional love and su...

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“…Conclusion ........................................................................................................................... xii Tables Table 3-1. Properties of the seismic velocity model (Burger et al, 1987;Eaton et al, 2006;Hunter et al, 2010;Crow et al, 2011;Bent et al, 2015) ............................................................. Table 3-2. The focal mechanism proposed for the Ladysmith earthquake 2014) .. ..................................................................................................................................................... Table 4-1.…”

Section: Prefacementioning

confidence: 99%

Three dimensional nonlinear simulation, sensitivity analysis and increasing the maximum frequency to 2.5 Hz using a physics-based method for basins in Ottawa, Canada

Esmaeilzadeh¹

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We performed 3-D nonlinear-viscoelastic ground motion simulations using a finite difference modeling method in a frequency range of 0.1 to 1 Hz in the Kinburn basin, Ottawa, Canada, for large earthquakes. Comparing the records and simulated velocity time series showed that regular viscoelastic simulations could model the ground motions at the rock and soil sites in the Kinburn basin for the Ladysmith earthquake (Mw=4.7). Using nonlinear-viscoelastic ground motion simulations for the scaled Ladysmith earthquake (Mw=7.5) significantly reduced the amplitude of the horizontal components of the Fourier spectrum and the predicted PGA and PGV values compared to regular linear viscoelastic simulations. Further, using a finite fault source (Mw=7) for the nonlinear-viscoelastic simulation decreased PGAs of the horizontal components. Our sensitivity analysis of simulations for different seismic moments showed that the PGV values exponentially increased with moment magnitude. Using a Gaussian source function with a short half duration increased the PGVs and the amplitude of velocity Fourier spectrum. Relaxation times and relaxation coefficients for viscoelastic simulation significantly increased PGV, the amplitude of the PSA ratio, and the velocity Fourier spectrum for a small earthquake. Employing a small soil Q model reduced PGV, PSA of soil/rock ratios, and the amplitude of velocity Fourier spectrum. Using finite fault model for a large earthquake (Mw =7) significantly reduced the PGV values relative to a point source model. We increased the maximum frequency to 2.5 Hz in FD modeling using a dual grid size method for two basins (Kinburn and Orleans basins in Ottawa, Canada). The simulated velocity time series from the dual grid size method provided better results compared to the results of the single grid size, although there were large differences between the amplitude of the velocity Fourier spectrum of the simulations and the amplitude of the records, particularly at low frequencies (<1 Firstly, I would like to express my sincere gratitude to my supervisor Prof. Dariush Motazedian for the continuous support of my Ph.D study and related research, for his patience, motivation, and immense knowledge. His guidance helped me in all the time of research and writing of this thesis. I could not have imagined having a better advisor and mentor for my Ph.D study. I would also wish to express my gratitude to Dr. James Hunter for extended discussions and valuable suggestions which have contributed greatly to the improvement of the thesis. I would also like to thank the research team, Steve, Sylvia, Sherry, Parisa, and Shutian who I learned a lot from them, through their personal and scholarly interactions, their suggestions at various points of my research. Thank you to my fellow grad students and the staff and faculty of the Department of Earth Sciences for the discussions on this topic and others. This research was supported by the Natural Sciences and Engineering Research Council of Canada under the Discovery Grant program and ...

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Monofrequency in situ damping measurements in Ottawa area soft soils

Cited by 24 publications

References 21 publications

Comprehensive nonlinear seismic ground response analysis of sensitive clays: case study—Leda clay in Ottawa, Canada

Comprehensive nonlinear seismic ground response analysis of sensitive clays: case study—Leda clay in Ottawa, Canada

A Hybrid Approach for Nonlinear Soil-Structure Interaction Analysis of Pile- Supported Bridges

Three dimensional nonlinear simulation, sensitivity analysis and increasing the maximum frequency to 2.5 Hz using a physics-based method for basins in Ottawa, Canada

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