May/June 2023 - 82

The installation of the rigid inclusions
and the associated large shear
strains appear to have produced a
change in the state of the clay, which
became less contractive than in its
original configuration. It is not known
whether this change occurred in
response to a structural change in the
particle arrangement, or to the state of
stresses, or both. Previous research
on expansion of cavities in soft clay
has shown that structural changes
can develop quickly after cavity
expansion within a certain radius, and
before full, overall pore pressure
dissipation in the medium.
Mitigation of Liquefaction
Potential
Calculated safety factors against
liquefaction for pre-installation CPTs in
the loose granular soil was generally
close to 1.0, with safety factors as low as
0.75 in localized zones. Densification of
the sand during installation of the rigid
inclusions increased the factor of safety
to values generally approaching 1.5.
This magnitude of improvement was
larger than was originally estimated. It
is important to note that these values
were determined at nodal CPT
locations, and thus it is expected that
equal or larger factor of safety values
developed closer to each rigid inclusion.
The increase in factor of safety
Pre-install CPT data
against liquefaction is obviously a
result of the increase in density of the
sand. However, it may also reflect the
increase in lateral stresses generated
by rigid inclusion installation. Because
the formulation used to estimate factor
of safety against liquefaction was
developed for normally consolidated
deposits (at-rest condition), it is
possible that the values of postinstallation
factor of safety are
somewhat overestimated; however, it is
clear that the factor of safety against
liquefaction increased significantly
over unity.
CPT-Based Design of Rigid
Inclusions
The data presented indicate that
installation of rigid inclusions significantly
changes the average density of
granular soils, and the lateral stresses
of any soil mass. However, modeling of
rigid inclusions commonly accounts for
the interaction between the soil, in its
original state, and the added rigid
inclusions. Therefore, it is likely that
typical rigid inclusion design is largely
conservative because it ignores the
Post-install CPT data
82 * DEEP FOUNDATIONS * MAY/JUNE 2023

May/June 2023

Table of Contents for the Digital Edition of May/June 2023

TOC
May/June 2023 - Intro
May/June 2023 - 1
May/June 2023 - 2
May/June 2023 - TOC
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