ETL 1110-2-544
31 Jul 95
embankment-foundation system based on data
Chapter 3
collected from settlement gages, slope indicators,
Embankment Construction Problems
pore pressure transducers, etc.
3-2. Important Features of Embankment
The analysis of embankment construction involves the
Construction Analysis
estimation of stresses and movements in embank-
ments and their foundations both during and after
The following paragraphs describe several items and
construction. The construction of embankments
considerations necessary for the performace of a good
generally involves both excavation and filling in
finite element model for embankment construction:
some specified order. The finite element method
offers an ideal way to perform such an analysis
a. Material behavior models. Soil is the
because of its ability to handle complex geometries,
primary material of construction in embankment
construction sequences, and nonlinear soil behavior.
construction problems. As described in the
Some examples of embankment construction
introduction of this ETL, the stress-strain behavior
problems include those in embankment dams,
of soil is nonlinear and inelastic. For all cases
levees, and highway embankments. Additionally, a
except saturated soil under undrained conditions,
static finite element analysis is often performed as
the stress-strain behavior of soil is dependent on
part of the evaluation of liquefaction potential of
confining pressure. These aspects of soil behavior
foundation soils beneath an embankment as the
are encountered in most geotechnical engineering
cyclic strength of soil depends on the state of stress
projects, including projects involving the
in the soil (Wahl et al. 1987).
construction of embankments. Consequently, it is
important that the material model be capable of
tracking these aspects of soil behavior. Many
3-1. Results and Use of Embankment
material models, such as the hyperbolic model of
Construction Analysis
Duncan and Chang (1970) and the Cam-Clay model
(Roscoe and Burland 1968), do capture these
a. Embankment and foundation system. The
characteristics of soils. The hyperbolic model uses
stresses and movements obtained from the analysis
a confining pressure-dependent, nonlinear elastic
can be used to evaluate the expected performance of
formulation, with an inelastic component
the embankment-foundation system against pre
introduced, because the value of the unload-reload
determined performance standards. The finite
modulus is larger than the value of the virgin
element analysis should be used in conjunction with
loading modulus. The Cam-Clay model uses a
a conventional slope stability stability program to
plasticity formulation that also yields reduced
ensure that both give the same results with respect
modulus values as the soil strength becomes
to the stability of the system.
mobilized and increased modulus values as the
confining pressure increases. One of the key
b. Finite element analysis. The finite element
benefits of plasticity is that it can model plastic
analysis can be a useful tool during the design
strains that occur in directions other than the
process of an embankment. Parametric studies can
direction of the applied stress increment. This
be performed for the purpose of dealing with
feature becomes especially important when a soil
uncertainty in the foundation conditions and
mass is near failure. In such a case, the application
material properties. The results of these studies can
of a load increment in one direction can cause large
provide a range of values for stresses and
displacements of the soil in another direction if
movements which can be compared with allowable
large forces had been previously applied in that
values to help ensure the adequacy of the design.
other direction. For well-designed structures, in
which failure of large masses of soil is not
c. Construction process. The finite element
imminent, modeling this aspect of failure can
analysis of an embankment can also be useful in the
become less important.
construction process, since it can serve as an aid in
the selection of the types and locations of in-
b. Stress-strain material properties values.
stumentation systems that monitor performance both
Selection of appropriate stress-strain material
during and after construction. This type of analysis
property values is often the most important step in
can also provide insight into the interpretation of
performing SSI analyses. There are four methods
movements and distribution of stress in the
to obtain material property values:
A-15
Previous Page
