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postgraduate thesis: Dynamic properties of granular materials at the macro and microscales

TitleDynamic properties of granular materials at the macro and microscales
Authors
Issue Date2012
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Gu, X. [顾晓强]. (2012). Dynamic properties of granular materials at the macro and micro scales. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4775262
AbstractDynamic properties of soil, including modulus and damping, play essential roles in evaluating the response of the soil deposit and its supporting structures when subjected to dynamic loads induced by earthquakes, traffic, explosions, machine foundations, and so on. It is well recognized that the dynamic properties of soil are affected by many factors, such as strain amplitude, stress condition, void ratio, saturation and gradation. Despite tremendous works have been done, the macroscopic effects of several key factors on the dynamic properties of granular material are not yet fully understood, due primarily to its particulate and multiphase nature. Furthermore, the understanding of how the influencing factors affect the dynamic properties of granular material or the underlying fundamental mechanism is inadequate. This study thus is carried out to investigate the effects and the underlying mechanisms of these important factors, including strain amplitude, stress condition, void ratio, particle size, saturation, and initial fabric, by means of advanced laboratory tests and numerical simulations. To study the dynamic properties at the macro scale, a series of laboratory tests are carried out in a state-of-art resonant column (RC) apparatus incorporating bender element (BE) and torsional shear (TS). Test materials include artificial glass beads with different sizes, commercially available standard sands and natural completely decomposed granite (CDG). The specimens are prepared at various densities, confined at different pressures, tested both in dry and saturated conditions, and reconstituted by different preparation methods. In particular, the characteristics of wave signals (both S-wave and P-wave) at various conditions and the associated interpretation methods in BE tests are investigated in detail. The results obtained from BE, RC and TS are compared to clarify the potential effect of test method. Moreover, attempts are made to explain the test results from the viewpoint of micromechanics. Numerical simulations using discrete element method (DEM) are performed to study the dynamic properties of granular materials and explore the underlying fundamental mechanism at the micro scale. The simulations indicate that the elastic properties are closely related to the coordination number and the distribution of normal contact forces in the specimen. The effects of initial fabric and induced fabric, which are respectively achieved by different specimen generation methods and the application of anisotropic stress states, are investigated. The anisotropy of the specimen and its evolution during shearing are also studied. The results indicate that the anisotropy is resulted from the spatial distributions of contact force and contact number. The modulus reduction curve and damping curve obtained from the simulations are compared with those from laboratory tests.
DegreeDoctor of Philosophy
SubjectGranular materials.
Dept/ProgramCivil Engineering
Persistent Identifierhttp://hdl.handle.net/10722/181472

 

DC FieldValueLanguage
dc.contributor.authorGu, Xiaoqiang.-
dc.contributor.author顾晓强.-
dc.date.accessioned2013-03-03T03:19:43Z-
dc.date.available2013-03-03T03:19:43Z-
dc.date.issued2012-
dc.identifier.citationGu, X. [顾晓强]. (2012). Dynamic properties of granular materials at the macro and micro scales. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4775262-
dc.identifier.urihttp://hdl.handle.net/10722/181472-
dc.description.abstractDynamic properties of soil, including modulus and damping, play essential roles in evaluating the response of the soil deposit and its supporting structures when subjected to dynamic loads induced by earthquakes, traffic, explosions, machine foundations, and so on. It is well recognized that the dynamic properties of soil are affected by many factors, such as strain amplitude, stress condition, void ratio, saturation and gradation. Despite tremendous works have been done, the macroscopic effects of several key factors on the dynamic properties of granular material are not yet fully understood, due primarily to its particulate and multiphase nature. Furthermore, the understanding of how the influencing factors affect the dynamic properties of granular material or the underlying fundamental mechanism is inadequate. This study thus is carried out to investigate the effects and the underlying mechanisms of these important factors, including strain amplitude, stress condition, void ratio, particle size, saturation, and initial fabric, by means of advanced laboratory tests and numerical simulations. To study the dynamic properties at the macro scale, a series of laboratory tests are carried out in a state-of-art resonant column (RC) apparatus incorporating bender element (BE) and torsional shear (TS). Test materials include artificial glass beads with different sizes, commercially available standard sands and natural completely decomposed granite (CDG). The specimens are prepared at various densities, confined at different pressures, tested both in dry and saturated conditions, and reconstituted by different preparation methods. In particular, the characteristics of wave signals (both S-wave and P-wave) at various conditions and the associated interpretation methods in BE tests are investigated in detail. The results obtained from BE, RC and TS are compared to clarify the potential effect of test method. Moreover, attempts are made to explain the test results from the viewpoint of micromechanics. Numerical simulations using discrete element method (DEM) are performed to study the dynamic properties of granular materials and explore the underlying fundamental mechanism at the micro scale. The simulations indicate that the elastic properties are closely related to the coordination number and the distribution of normal contact forces in the specimen. The effects of initial fabric and induced fabric, which are respectively achieved by different specimen generation methods and the application of anisotropic stress states, are investigated. The anisotropy of the specimen and its evolution during shearing are also studied. The results indicate that the anisotropy is resulted from the spatial distributions of contact force and contact number. The modulus reduction curve and damping curve obtained from the simulations are compared with those from laboratory tests.-
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.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.source.urihttp://hub.hku.hk/bib/B47752622-
dc.subject.lcshGranular materials.-
dc.titleDynamic properties of granular materials at the macro and microscales-
dc.typePG_Thesis-
dc.identifier.hkulb4775262-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplineCivil Engineering-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.5353/th_b4775262-
dc.date.hkucongregation2012-

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