DFI Magazine May/June 2020 - 55

Research for Updated Guide to
Support Fluids for Deep Foundations
DFI previously highlighted the work that
the EFFC and DFI undertook to reduce the
quality issues encountered by using tremie
concrete in drilled shafts and diaphragm
walls, which led to the publication of the
second edition of the EFFC/DFI Guide to
Tremie Concrete for Deep Foundations. Given
the clear linkage between tremie concrete
and support fluid in both foundation
elements, the EFFC and DFI Concrete Task
Group identified the need for a greater
review of the characteristics, testing and
management of support fluids. This focus
subsequently resulted in the publication of
the first edition of the Guide to Support
Fluids for Deep Foundations in March 2019.
This guide was groundbreaking in
many ways, and will serve as a valuable
reference in the future. It was the first time
that the collective knowledge pool of good
practice from around the world was
brought together into a single authoritative
publication. A second edition is already
planned, which will be based on an
extensive field research study that is being
funded by EFFC, DFI, contractors,
consultants and suppliers. It is also hoped
that the study will forge links with
academics working on support fluids,
which already includes numerical
modelling, polymer fluids testing, trench
stability investigations, influence of fluid
type on side friction, and the influence of a
support fluid on the bond strength
between a reinforcement and concrete cast
in a support fluid.
The research to develop the upcoming
edition has been divided into two parts.
The first is focused on obtaining contractors' standard fluid test data from sites
in North America and Europe; second,
other data is being obtained from the study,
which is being led by two independent
specialists. These specialists are spending
three to four days each on a total of 20
different project sites that were proposed
for inclusion by contractors in the U.S. and
Europe. The study involves a series of
nonstandard tests, new procedures and test

equipment to improve support fluid management and develop a better comprehension of support fluid behaviour.
The study will run until mid-2021 and
has the following primary objectives:
* Record properties of fresh, excavation
and recycled/cleaned fluid
* Establish a property/depth profile for
the excavation fluid
* Compare excavation base hardness
methods and tools
* Compare commonly used fluid
samplers
* Investigate the accuracy of concrete
depth indicators
* Record concrete levels during casting
inside and outside the cage
* Obtain and test fresh and hardened
samples from the interface layer
* Test fresh concrete properties
The project stakeholders are grateful to the
contractors that have so far volunteered to
give access to their projects, so that
independent specialists can implement the
study. This has been designed specifically
to limit possible production time losses on
site. Before access onto a site, a detailed
planning discussion is held with the site
team and any necessary inductions are
carried out. All information obtained
during site visits is treated as strictly
confidential by the specialists and is only
disclosed to members of the Task Group
who have signed a detailed confidentiality/
nondisclosure agreement. Contractors who
have allowed testing on their site will be
allowed to check and approve the draft of
the second edition before publication.
The site testing involves performing
standard tests on the fluid at different stages
(fresh, during excavation, after cleaning
and prior to concreting). Alternative
procedures to measure the fluid density
will be evaluated, as the Task Group
identified a limitation in the accuracy of the

standard mud balance for measuring fluid
density (especially polymer-based support
fluid); the target is to increase the
measurement accuracy from 0.01 g/ml to
0.005 g/ml. Other nonstandard tests will be
carried out that are aimed at measuring the
fluid rheological parameters such as
apparent viscosity, gel strength and fine
content in polymer support fluids.
Data acquired to date is proving
invaluable and the Task Group is optimistic
that, as more sites are visited, the quality
and volume of data will enable good
practice and procedures to be 'fine-tuned'
in the second edition. Of course, more sites
are required, and DFI would be interested
in hearing from anyone that may wish to
contribute to the study and ultimately to
the findings that will define the content of
the latest edition of the EFFC/DFI Guide to
Support Fluids for Deep Foundations. For
more information, contact Peter Faust at
pfaust@malcolmdrilling.com or Mary
Ellen Bruce Large, DFI director of technical
activities, at melarge@dfi.org.
If all goes according to plan, the second
edition of the Guide to Support Fluids for
Deep Foundations will be published in
2021/2022. But in the meantime, the first
edition is available for free download at
www.dfi.org or www.effc.org.

This article was written by Peter Faust, vice president of business development, Malcom Drilling.

DEEP FOUNDATIONS * MAY/JUNE 2020 * 55

DFI Magazine May/June 2020

Table of Contents for the Digital Edition of DFI Magazine May/June 2020