Study of small strain dynamic properties of sands and silty sands

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Copyright: Payan, Meghdad
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Abstract
Shear modulus (G), Young’s modulus (E) and damping ratio (D) are key properties of soils which play fundamental roles in the analysis and design of geotechnical structures subjected to static and dynamic loading. Of particular interest for geotechnical engineers are the values of these properties at the range of small strains. The aim of this study is to investigate the influence of different parameters on the small-strain dynamic properties of sands and silty sands. The contributions made in the thesis include: i) A novel approach is proposed for the examination of the validity of stiffness models in capturing the effects of void ratio and confining pressure on the small-strain behaviour of granular soils; ii) Considering the significant influence of particle shape, new expressions for the evaluation of G_max and E_max for dry and saturated sands are proposed and validated using the results of a comprehensive set of torsional and flexural resonant column tests performed at a range of void ratios, confining pressures, particle shapes and grain size distributions. Adopting the theory of elasticity, the variation of Poisson’s ratio with the index properties of sands is also captured; iii) The influence of particle shape on the small-strain damping ratio of dry sands in shear (D_(s,min)) is studied through a comprehensive set of torsional resonant column tests. The effects of grain size distribution, particle shape and effective confining stress are incorporated into a general expression of D_(s,min) for the evaluation of the small-strain damping ratio of sands; iv) Based on a comprehensive set of experimental data, new models for the prediction of small-strain dynamic properties of sand-silt mixtures are developed. It is shown that while at low percentages of fines content, there is a significant difference between the dynamic properties of various types of sands, this variation will diminish as fines content of the mixture increases. In particular, beyond a specific percentage of fines content, the soil behaviour becomes thoroughly silt-dominant, rendering no significant influence of different sand properties on the small-strain shear and Young’s moduli, Poisson’s ratio and damping ratio; v) The influence of stress anisotropy on the small-strain shear modulus of sands are evaluated and a new G_max model is developed incorporating the contributions of grain size characteristics and particle shape in the prediction of G_max of sands subjected to stress anisotropy. It is shown that the influence of stress anisotropy on the small-strain shear modulus of sands is more pronounced for sands with irregularly shaped grains and wider grain size distributions as opposed to uniform sands of relatively rounded and spherical grains; vi) Finally, the proposed expression for the prediction of the small-strain shear modulus of dry and saturated sands is extended to evaluate the shear modulus of variably saturated sands incorporating the effective stress approach. Accordingly, the model is examined against several sets of experimental data from the literature as well as this study. It is shown that the proposed model for saturated sands can be applied to unsaturated sands satisfactorily provided that a correct effective stress framework is adopted.
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Author(s)
Payan, Meghdad
Supervisor(s)
Khoshghalb, Arman
Khalili, Nasser
Senetakis, Konstantinos
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Publication Year
2017
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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