May/June 2023 - 83

Pre- and post-installation liquefaction
effect of the change in density and or
lateral stress on the stiffness of the soil.
This presumed, inherent conservatism
likely causes unnecessary
additional costs to the ground modification
scheme. However, there is not
sufficient published information to
permit an accurate estimate of the
improvement of the properties and state
of stress of soil. Therefore, it seems
prudent that pre- and post-installation
CPT campaigns be implemented to
permit more efficient designs and to
verify them.
CPT-Aided Quality Control
Another important use of the CPT is for
quality control during installation of
rigid inclusions. Installation of each
rigid inclusion is akin to a large-scale
soil probe with continuous MWD data.
The difficulty lies in how to interpret
the data from each of these " tests " to
assess whether the rigid inclusion
meets the minimum requirements of
axial resistance for the project, or if
there are localized variations of
concern in soil conditions. Most
importantly, proper interpretation of
these data may permit reduction of
rigid inclusion length as needed due to
beneficial variations in the soil profile,
which may be natural or caused by
progressive densification of the soil as
production progresses.
The authors have developed a
procedure that incorporates CPT data as
an integral part of a performance
assessment and quality control method.
It consists of the following:
* Pre-installation CPT campaign,
including CPT probes at load test
locations
* Installation of test rigid inclusions
and acquisition of automated
installation data
* Development of a resistance index
plot for the test rigid inclusion based
on installation data
* Correlation of resistance index to
CPT data and load test data
* Use of the resistance index plot of
the test elements as baseline for
comparison to the resistance index
of production rigid inclusions
This procedure is useful for assessment
of installed rigid inclusions, and
less qualitative than examining large
quantities of installation logs visually.
The combined use of CPT, load testing
and MWD data provides a quantitative
way to detect potential variations in
rigid inclusion installation that may be
a concern.
It is important to note that only
trends are important when treating
large areas. One anomalous rigid
inclusion will not have a significant
effect on the quality of the treatment.
However, a pattern of significantly lower
resistance index values within an area
encompassing a number of rigid inclusions
may be an indication that additional
attention should be placed on that
area. Similarly, a pattern of significantly
higher resistance index values could
justify reducing the length of rigid
inclusions going forward in that area.
DEEP FOUNDATIONS * MAY/JUNE 2023 * 83

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
May/June 2023 - 4
May/June 2023 - 5
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