March/April 2022 - 87

flight auger (CFA) piles that would have
been 2.6 ft (0.8 m) in diameter because
of a tight differential settlement criterium
of 1:550. Instead, it was successfully
founded on DSM columns.
DSM Use Decisions
Answering the appropriate use question
is essential not only to geotechnical
contractors, but to consultants, designers
and clients. The following
indicators may help identify the proper
DSM technology and its applicability:
Indicator 1: Soil type and water
Deep soil mixing for Warsaw residential building
bearing pressure under the foundation
ring of a 230 ft (70 m) high ash container.
To meet tight settlement and tilt criteria,
a two-step ground improvement
scheme was implemented.
Firstly, the sand layer, about 39 ft
(12 m) thick, was improved and homogenized
with bottom feed vibro compaction
to avoid differential settlements
resulting from a strongly variable
degree of initial compaction. Secondly,
DSM columns, 19.7 ft (6 m) long and 3.9 ft
(1.2 m) in diameter, were executed under
the foundation ring to increase
subsoil stiffness directly under the foundation
ring. This example also demonstrates
how easily different GI technologies
can be combined with DSM.
Finally, a large commercial center
PLAZA in Rybnik, comprising 205
heavily loaded pad foundations,
initially was designed on continuous
content. We have found that wet mixing
is rational if the moisture content is
below 120%. Good stabilization of sandy
and clayey soils is generally achievable.
With respect to organic soils, it is
well-known that the neutralization of
humic and fulvic acids leads to a
specific binder quantity that has to be
exceeded before the remaining binder
contributes to the strength increase.
Therefore we consider organic content
of 20% as a practical limit for a competitive
use of DM. However, we have
abandoned the application of DM in
case of thick deposits of organic soils.
Indicator 2: Exposure to aggressive
groundwater or soil. In this respect we
follow the recommendation of the
Eurocode and use specific binders
and/or reduced design column diameter
to mitigate or minimize potential
negative impacts.
Indicator 3: Comprises site-specific
conditions and is self-explanatory.
Indicator 4: The type of structure,
loading conditions and the design
requirements. This ending placement
might be surprising, but experience has
taught us that DSM can be safely applied
to a large variety of foundation problems.
Of course, we maintain a healthy
engineering judgement, and move to
new mixing applications with due care.
Summarizing, we can consider
idealized settlement versus foundation
pressure on a graph. For an exemplary
DSM design, marked with point 1, the
associated settlement corresponds to a
DSM use after sand compaction for ash container
DEEP FOUNDATIONS * MAR/APR 2022 * 87

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Table of Contents for the Digital Edition of March/April 2022

TOC
March/April 2022 - Intro
March/April 2022 - 1
March/April 2022 - 2
March/April 2022 - TOC
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