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A Soil-Water Coupled Analysis on the Effect of
Improvement of a Loose Sandy Ground by Cylindrical Cavity Expansion
Toshihiro Noda, Masaki Nakano, Kazunori Mizuno and
Hidekatsu Takeuchi
ABSTRACT : Sand packed loosely
exhibits a softening with plastic volume compression under undrained
shear condition, while sand packed densely exhibits a hardening with
plastic volume expansion under the same condition. Using the Cam-clay
model with super-subloading yield surfaces (Asaoka et. al., 2000), which
describe the loss of structure and the decay of overconsolidation of
soil can simulate these typical behaviors. In the present study, in
order to clarify the mechanism of compaction of sand based on the elasto-plastic
mechanism, we numerically examine the compaction of loose sand ground by
repeated expansion of a soil pile through the soil-water coupled finite
deformation analysis of the new soil model. The new findings in the
present study are as follows. (1) The loose sand ground, of which the
structure is initially high, can be compacted by the repeated expansion
of a soil pile, due to a hardening with plastic volume compression by
the loss of structure even with a relatively small plastic deformation.
(2) The overconsolidation ratio of the sand increases and the sand
ground becomes stable by the repeated unloading process after the
expansion. (3) Owing to these effects, the sand ground is easy to be
compacted by a small driving force below the capacity of the machine.
The effects of soil improvement by the compaction, such as the increase
in the coefficient of lateral pressure and the increase in the shear
strength of sand elements and so on, are expressed.Key words: compaction,
elasto-plasticity, overconsolidation, numerical analysis, sand,
structured soil (IGC: D9)
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