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postgraduate thesis: Cyclic behaviour and liquefaction resistance of silty sands

TitleCyclic behaviour and liquefaction resistance of silty sands
Authors
Advisors
Advisor(s):Yang, J
Issue Date2017
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Wei, X. [魏驍]. (2017). Cyclic behaviour and liquefaction resistance of silty sands. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.
AbstractRecent earthquake events revealed that liquefaction of silty sands remains an unsolved issue even after decades of investigations. Difficulties in estimating the liquefaction resistance of sands arise from combined effects of various factors such as fines content, gradation, particle shape, plasticity, initial static shear stress, and so on. Current practice of liquefaction evaluation relies heavily on empericism and lacks solid theoretical background. The present study investigated the cyclic behaviour and liquefaction resistance of silty sands under the framework of critical state soil mechanics. A systematic cyclic triaxial test programme was accomplished, covering different fines contents, particle shape, particle size disparity ratios and relatively wide range of initial states. Literature database was also compiled, regarding the critical state lines and cyclic resistance of silty sands, to enable further characterisation and analysis. Four typical cyclic failure patterns were identified. They were found dependent on initial state of the specimen and cyclic loading characteristics. A series of characteristic charts of cyclic loading were proposed to predict the cyclic failure patterns based on cyclic-monotonic correspondence. The cyclic resistance (CRR) of silty sands with different fines contents was unified by the state parameter (ψ) for various initial static shear stress ratio (α). Moreover, the CRR-ψ correlation for α = 0 was unified for different siliceous sands with similar initial fabric by comparison with literature data. A simple empirical method was proposed to estimate the critical state line parameters of silty sands. Collective application of the unified CRR-ψ correlation and the estimated critical state lines predicted the CRRs of non-plastic silty sands fairly well for similar initial fabric. The effects of initial static shear stress were also characterised through CRR-ψ correlations. The initial static shear stress correction factor (Kα) and overburden pressure factor (Kσ) were derived from the CRR-ψ correlations. The Kα factor was found dependent on the initial state of the soil. The Kσ factor was found dependent on initial density, properties of soil, and α. These behaviours should be considered in engineering practice. A shear wave velocity based liquefaction assessment chart (CRR-Vs1 chart) was derived from the unified CRR-ψ correlation and the unified Vs1-ψ correlation. The derived curve indicated a unified correlation regardless of fines content for a given series of sand-silt mixtures. Factors affecting the correlation were also discussed. This approach provides a new perspective to investigate the soil behaviours regarding the CRR-Vs1 correlation, other than purely empirical methods. A critical state constitutive model was modified for non-plastic silty sands, by implementing the unified elastic shear modulus formulation. With the critical state parameters predicted by the newly proposed method in the present study, the model was able to simulate the monotonic and cyclic behaviour of silty sands with various fines contents.
DegreeDoctor of Philosophy
SubjectSoil liquefaction
Dept/ProgramCivil Engineering
Persistent Identifierhttp://hdl.handle.net/10722/274657

 

DC FieldValueLanguage
dc.contributor.advisorYang, J-
dc.contributor.authorWei, Xiao-
dc.contributor.author魏驍-
dc.date.accessioned2019-09-09T07:21:26Z-
dc.date.available2019-09-09T07:21:26Z-
dc.date.issued2017-
dc.identifier.citationWei, X. [魏驍]. (2017). Cyclic behaviour and liquefaction resistance of silty sands. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.-
dc.identifier.urihttp://hdl.handle.net/10722/274657-
dc.description.abstractRecent earthquake events revealed that liquefaction of silty sands remains an unsolved issue even after decades of investigations. Difficulties in estimating the liquefaction resistance of sands arise from combined effects of various factors such as fines content, gradation, particle shape, plasticity, initial static shear stress, and so on. Current practice of liquefaction evaluation relies heavily on empericism and lacks solid theoretical background. The present study investigated the cyclic behaviour and liquefaction resistance of silty sands under the framework of critical state soil mechanics. A systematic cyclic triaxial test programme was accomplished, covering different fines contents, particle shape, particle size disparity ratios and relatively wide range of initial states. Literature database was also compiled, regarding the critical state lines and cyclic resistance of silty sands, to enable further characterisation and analysis. Four typical cyclic failure patterns were identified. They were found dependent on initial state of the specimen and cyclic loading characteristics. A series of characteristic charts of cyclic loading were proposed to predict the cyclic failure patterns based on cyclic-monotonic correspondence. The cyclic resistance (CRR) of silty sands with different fines contents was unified by the state parameter (ψ) for various initial static shear stress ratio (α). Moreover, the CRR-ψ correlation for α = 0 was unified for different siliceous sands with similar initial fabric by comparison with literature data. A simple empirical method was proposed to estimate the critical state line parameters of silty sands. Collective application of the unified CRR-ψ correlation and the estimated critical state lines predicted the CRRs of non-plastic silty sands fairly well for similar initial fabric. The effects of initial static shear stress were also characterised through CRR-ψ correlations. The initial static shear stress correction factor (Kα) and overburden pressure factor (Kσ) were derived from the CRR-ψ correlations. The Kα factor was found dependent on the initial state of the soil. The Kσ factor was found dependent on initial density, properties of soil, and α. These behaviours should be considered in engineering practice. A shear wave velocity based liquefaction assessment chart (CRR-Vs1 chart) was derived from the unified CRR-ψ correlation and the unified Vs1-ψ correlation. The derived curve indicated a unified correlation regardless of fines content for a given series of sand-silt mixtures. Factors affecting the correlation were also discussed. This approach provides a new perspective to investigate the soil behaviours regarding the CRR-Vs1 correlation, other than purely empirical methods. A critical state constitutive model was modified for non-plastic silty sands, by implementing the unified elastic shear modulus formulation. With the critical state parameters predicted by the newly proposed method in the present study, the model was able to simulate the monotonic and cyclic behaviour of silty sands with various fines contents.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subject.lcshSoil liquefaction-
dc.titleCyclic behaviour and liquefaction resistance of silty sands-
dc.typePG_Thesis-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplineCivil Engineering-
dc.description.naturepublished_or_final_version-
dc.date.hkucongregation2017-
dc.identifier.mmsid991044139572803414-

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