Design of Rigid Inclusions for Embankment Support considering Load Transfer and Installation Effects
Rigid inclusions are grouted or cemented columns
used to improve soft soils. They have
been increasingly used in practice in the United States, mostly for embankment
support in transportation applications.
There are several types of equipment available in the market to install
rigid inclusions with different trade names (e.g., controlled modulus columns,
grouted impact piers, cast-in-place ground improvement elements, and augered
pressure grout columns). Installation of
some of these columns causes full displacement of their surrounding soils,
while others result in partial displacement. Installation procedures for rigid inclusions
and their effects on soils depend on the type of equipment and the type of soil
and are therefore different. Rigid
inclusions are often installed under a load transfer platform to support
embankment loads. Different equipment
and installation procedures may cause ground subsidence and/or heave as well as
lateral displacement; change the properties of the surrounding soils at
different distances and depths; and affect load transfer of rigid inclusions in
these soils. Downdrag forces often exist
within the upper portion of rigid inclusions under embankments. The distribution of the downdrag forces is
hard to determine. Rigid inclusions
under the slopes of embankments are subjected to lateral thrust in addition to
axial and downdrag forces. Bending
resistance of rigid inclusions is one of the design issues. Unfortunately, no well-accepted design
methods are available to consider load transfer in rigid inclusions subjected
to vertical and/or lateral loads and installation effects on their surrounding
soils. No well-established design
guidelines are available for the thickness of the load transfer platform and the
engineering properties of platform fill.
Research is needed to quantify installation effects from different
equipment on different soil types and develop design methods considering their
effects in load transfer analysis of rigid inclusions in soils.
The main objective of the proposed research is to
quantify installation effects of different equipment on different soil types
and develop a design method considering their effects in load transfer analysis
of rigid inclusions in soils subjected to vertical and lateral loads from
embankments. The design method will take
into consideration ground movement during installation, changed properties of
the surrounding soils after installation, load distribution along rigid
inclusions, including toe and side resistance including downdrag forces, lateral
resistance of rigid inclusions in slope stability analyses, and the effect of
the load transfer platform.
benefits of developing the design method for rigid inclusions for embankment
appropriate means to quantify ground movement during installation by different
equipment in different soils
improved properties of the surrounding soil to create a more economical
safety through comprehensive and consistent design considerations (e.g.,
downdrag force and bending resistance) using rigid inclusions
Basu et al. (2010) presented the common practice
and design of drilled displacement piles.
Simon (2012) provided a brief summary of definition, functions,
installation techniques, advantages and drawbacks, load transfer mechanisms,
design considerations, and points requiring further research for rigid
inclusions*. *ASIRI (2013) developed recommendations for
the design, construction, and control of rigid inclusion ground improvements,
mainly for building applications. BS
8006-1: 2010 (2010) developed a detailed procedure for designing load transfer
platforms over rigid inclusions considering underlying voids, which is very
conservative. This RNS calls for the
development of a similar document for rigid inclusions for transportation
proposed research consists of the following tasks:
1: Review Literature and Assess Current Practices
task includes a comprehensive review of national and international practices
for use of rigid inclusions in building applications and transportation
earthworks, categorizes different installation equipment and methods, and
identifies gaps in understanding of installation effects and load transfer and
design of rigid inclusions for embankment support.
2: Evaluate Installation Effects on
appropriate studies to evaluate installation effects of rigid inclusions by
different equipment and installation methods on different soils (clay and sand). The studies can be physical model tests,
field tests, and/or numerical analysis.
The evaluation should include but not be limited to ground movement
at different distances and depths and changed properties (e.g., density,
strength, and modulus).
3: Evaluate load transfer of rigid inclusions under embankments
appropriate studies to evaluate load distributions along rigid inclusions in
soils after installation subjected to vertical and lateral loads. The studies should include but not be
limited to toe resistance, side friction (including downdrag force), axial
capacity, bending resistance of rigid inclusions, and effects of load transfer
platforms on load transfer. Field
monitoring of a constructed embankment on rigid inclusions is desired.
4: Develop a design method for rigid inclusions under embankments
Develop a comprehensive design method for use of rigid inclusions in
soils for embankment support. The design
method should include but not limited to ground movement during
installation, changed properties of surrounding soils after installation, layout
and length of rigid inclusions, load distribution, axial capacity, bending
resistance of rigid inclusions, and settlement and stability of embankments.
A budget of $450,000 is estimated.
This research will serve as a basis for
development of an implementation plan to be included in FHWA GEC 13 Ground
Modification Methods - Reference Manual and design and construction guidance to
be included in the AASHTO Bridge Specifications.
Federal and State DOTs, Researchers; representatives from the following departments have indicated this RNS is a critical need: Louisiana Department of Transportation and Development, Ohio Department of Transportation, New Mexico Department of Transportation, Illinois Department of Transportation, and Minnesota Department of Transportation.
|Sponsoring Committee:||AFS10, Transportation Earthworks
|Research Period:||Longer than 36 months|
|RNS Developer:||Jie Han, University of Kansas; Antonio Marinucci, V2C Strategists, LLC; Jesse Rauser, Louisiana Department of Transportation and Development|
|Source Info:||Cosponsoring Committees|
AFS20 Standing Committee on Geotechnical Instrumentation and Modeling
AFS30 Standing Committee on Foundations of Bridges and Other Structures
AFS40 Standing Committee on Subsurface Soil-Structure Interaction
|Index Terms:||Embankments, Soil structure interaction, Load transfer, Installation, Columns, |
|Cosponsoring Committees:||AFS20, Geotechnical Instrumentation and Modeling; AFS30, Foundations of Bridges and Other Structures; AFS40, Subsurface Soil-Structure Interaction|
Bridges and other structures