March/April 2022 - 86

A2 Remediation with Piling
Two short comments on the design
practice in Poland. Unlike other countries,
we distinguish between two
classes of DSM application, and allow for
two different confidence levels while
determining the characteristic compressive
strength of soil mixes based on
the log-normal distribution. This approach
allows use of slightly higher
characteristic compressive strength (fck)
values
f class B applications, associor
ated
with settlement reduction only.
Based on our experience with
were not sufficient to stop further
heave. In parallel, intensive analyses
were conducted to find out the real
cause of the observed anomaly.
We knew from the site investigation
report that the clay contained gypsum
crystals, but were not aware that
ettringite formation could occur in
connection with DSM works. Ettringite
forms from a reaction between calcium,
alumina, sulphate and water. These
materials are provided as follows:
* calcium is contained in cement
* alumina is present in cement and
also in clay minerals
* sulphates were profusely present in
the soil as gypsum or anhydrite
* water was in the ground and also in
the slurry
The formation process may include not
only new ettringite building, but also a
conversion of the existing ettringite,
both leading to a significant volumetric
expansion.
A similar case from southern
Germany has been reported by Rolf
Katzenbach, Prof. Dr.-Ing., and his coworkers
at TU Darmstadt, although
associated with jet grouting works (see
Deep Mixing Conference 2021 paper
PID 1232052). Follow-up research has
revealed that the influence of type and
number of clay minerals is important,
but several other conditions help
initiate development of the delayed
ettringite mechanism. Consequently,
further research is needed on the
formation of ettringite in binderstabilized
soils.
Finally, once the real enemy was
identified, it was decided to remove all
pad foundations and the treated ground
in between. The new foundations were
supported on steel micropiles designed
to carry compressive as well as tensile
forces.
typical Polish soils, we also utilize in
the design the characteristic compressive
strength determined for 60
days of curing. Based on many tests,
we assume that the
f at 60 days is
ck
typically 1.25 times higher than after
28 days. Furthermore, we also allow
for QC to use a factor of 0.8 when
testing specimens which have cured
for 28 days.
The following comprise selected
national project examples:
Residential buildings often require
piling because of heavily loaded pillars
and walls. In the 19-floor part of a
building in Warsaw, the structure was
founded on 193 DSM columns. The red
numbers represent concentrated load
in kN on a particular pillar, and the
green numbers, line loads in kN/m.
Using DSM was cost effective compared
to piling. This demonstrates that
DSM can carry very high and concentrated
loads, maintaining all the
design criteria.
Another project includes high loads,
equivalent to 162 4 si (1 12 M a)
. p
.
P
PAT Library
86 * DEEP FOUNDATIONS * MAR/APR 2022
March/April 2022

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