Dynamic 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. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/181472 |
| Date | January 2012 |
| Creators | Gu, Xiaoqiang., 顾晓强. |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47752622 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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