September/October 2021 - 102

www.geoinstitute.org/geotechtools/
(the recent login accessible home for the
FHWA manual content that was at
www.geotechtools.org). However,
acceptance criteria should be project
and purpose specific to meet individual
project requirements and deep mixing
quality goals.
We note however, that it is now
Japanese engineers were keen to share DM knowledge during a 2004 Tokyo technical visit
Poland, in 2020. Conferences and
workshops in Japan and Scandinavia
have also been excellent opportunities
to share experiences and learn from the
original developers of the methods.
It is, however, timely to reevaluate
certain aspects of the deep mixing
industry, as the authors did recently
with colleague David S. Yang, Ph.D.,
while presenting much of this paper as
a keynote for DFI's online Deep Mixing
Conference in June. In particular, the
authors have developed strong views
on deep mixing specifications and
quality assessment based on recent
experiences on major projects such as
LPV111 in Louisiana, and Herbert
Hoover Dike in Florida. In certain ways,
these issues are magnified in myriad
smaller projects located primarily on
the Eastern and Western seaboards.
Standards And Specifications
It remains difficult to fully standardize
design and acceptance criteria across
the U.S. market, given its great geographical,
technical and application
diversity. Guide specifications are
given in the Federal Highway Administration
Design Manual: Deep Mixing for
Embankment and Foundation Support,
(FHWA-HRT-13-046, 2013) and at
typical for specified performance
criteria to exceed the design demand; we
speculate that this arises from misunderstanding
the long-term performance
goals of the final deep mixing
product. DMM have been widely used
worldwide for only about 50 years -
barely the life expectancy of most
projects, with little published research
on the long-term durability of older DM
installations. For example, the generally
adopted criterion for maximum permeability
(1x10 cm/s) and minimum
unconfined compressive strength of
100 psi (0.7 MPa) specified for seepage
barrier walls should be justified as
specific design requirements. These
values are often used as default criteria,
but are adopted from prior projects
without sound technical reasons.
-6
Quality Assessment
Depending on the DM application, and
the specified acceptance criteria, some
or all of the following factors are
evaluated on each project:
* Verticality of individual elements
* Compressive strength and permeability
of the treated ground
* Locations and dimensions of the
elements
* Homogeneity of the treated soil
material and continuity (overlap) of
adjacent elements
Site of LVP111, the largest U.S. deep mixing levee project
102 * DEEP FOUNDATIONS * SEPT/OCT 2021
Compressive Strength: As noted above,
100 psi (0.7 MPa) is commonly specified
for the unconfined compressive
strength (UCS) of deep mixing seepage
barriers for dams and levees. Deep
mixing elements used for foundation
support or embankment reinforcement
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September/October 2021

Table of Contents for the Digital Edition of September/October 2021
