<p>This thesis investigates the effects of sample preparation methods, which has
substantial influence on the internal structure or fabric of the sample, and interparticle
locking on the behaviour of sand through experimental study. Extensive laboratory tests
were conducted on two sands (namely, Ottawa sand and crushed limestone) with distinct
particle shape and surface texture, using a Bishop-type triaxial testing system.</p><p>A total of eight sample preparation methods were used to fabricate specimens
with different initial fabric, with specimens being fabricated using water pluviation,
moist tamping, and moist rodding. The experimental data reveal that sample preparation
methods have significant effect on both deformation characteristics and shear strength of
sand, in addition to the density and the effective confining pressure applied to the
specimens. More specifically, water pluviation and moist tamping tend to yield
specimens of high anisotropy and large dilation, which in turn results in higher friction
angle in conventional triaxial compression. The effect of sample preparation methods
was also observed from undrained tests on saturated sand.</p><p>Laboratory tests on crushed limestone consisting of angular particles
demonstrate that strong interparticle locking may develop owing to particle angularity.
The shear resistance of sand with angular particles has contributions from interparticle
friction, dilatation and interparticle locking. Moreover, interparticle locking, which
largely exists at the peak shear resistance of sand but vanishes with dilation at large
deformation, exists under both low and high stress levels investigated in this study. A conceptual model was proposed to take into account the energy consumption associated
with breaking interparticle locking during deformation when estimating the dilatancy
and strength of granular soils.</P><P>The behaviour of sand along proportional strain paths was also investigated, with
the focus being placed on strain softening and material instability in the context of Hill's
second order work. Depending on the strain path or the deformation history, a dilatant
sand displaying hardening and stable behaviour under isochronic (undrained) conditions,
which is often used as a reference in soil mechanics, may succumb to unstable flow type
behaviour along dilative strain paths. More specifically, when the imposed rate of dilation
exceeds the inherent rate of dilation of the material, a dense sand specimen will have flow
failure similar to that of a saturated loose specimen subjected to undrained compression.
On the other hand, a loose sand may not have a flow failure when it is forced to have
contractive volume change along imposed strain paths.</P> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/21796 |
| Date | January 2007 |
| Creators | Su, Xubin |
| Contributors | Guo, P. J., Civil Engineering |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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