This dissertation evaluates the behavior of Geosynthetic-Reinforced Soil (GRS)
retaining structures under various soil stress states, with specific interest in the
development and distribution of soil and reinforcement stresses within these structures.
The stress distribution within the GRS structures is the basis of much of the industry’s
current design. Unfortunately, the stress information is often not directly accessible
through most of current physical testing and full-scale monitoring methods. Numerical
simulations like the finite element method have provided good predictions of
conservatively designed GRS structures under working stress conditions. They have provided little insight, however, into the stress information under large soil strain
conditions. This is because in most soil constitutive models the post-peak behavior of
soils is not well represented. Also, appropriate numerical procedures are not generally
available in finite element codes, the codes used in geotechnical applications. Such
procedures are crucial to properly evaluating comparatively flexible structures like GRS
structures. Consequently, this study tries to integrate newly developed numerical procedures
to improve the prediction of performance of GRS structures under large soil strain
conditions. There are three specific objectives: 1) to develop a new softening soil model
for modeling the soil’s post-peak behavior; 2) to implement a stress integration algorithm,
modified forward Euler method with error control, for obtaining better stress integration
results; and 3) to implement a nonlinear reinforcement model for representing the
nonlinear behavior of reinforcements under large strains. The numerical implementations
were made into a finite element research code, named Nonlinear Analysis of
Geotechnical Problems (ANLOG). The updated finite element model was validated
against actual measurement data from centrifuge testing on GRS slopes (under both
working stress and failure conditions).
Examined here is the soil and reinforcement stress information. This information
was obtained from validated finite element simulations under various stress conditions.
An understanding of the actual developed soil and reinforcement stresses offers important
insights into the basis of design (e.g., examining in current design guidelines the design
methods of internal stability). Such understanding also clarifies some controversial
issues in current design. This dissertation specifically addresses the following issues: 1)
the evolution of stresses and strains along failure surface; 2) soil strength properties (e.g.,
peak or residual shear strength) that govern the stability of GRS structures; 3) the
mobilization of reinforcement tensions.
The numerical result describes the stress response by evaluating the development
of soil stress level S. This level is defined as the ratio of the current mobilized soil shear
strength to the peak soil shear strength. As loading increases, areas of high stress levels
are developed and propagated along the potential failure surface. After the stress levels
reach unity (i.e., soil reaches its peak strength), the beginning of softening of soil strength is observed at both the top and toe of the slope. Afterward, the zones undergoing soil
softening are linked, forming a band through the entire structure (i.e., a fully developed
failure surface). Once the band has formed and there are a few loading increments, the
system soon reaches, depending on the tensile strength of the reinforcements, instability.
The numerical results also show that the failure surface corresponds to the locus of
intense soil strains and the peak reinforcement strain at each reinforcement layer. What
dominates the stability of GRS structures is the soil peak strength before the completed
linkage of soil-softening regions. Afterward, the stability of GRS structures is mainly
sustained by the soil shear strength in the post-peak region and the tensile strength of
reinforcements. It was also observed that the mobilization of reinforcement tensions is
disproportional to the mobilization of soil strength. Tension in the reinforcements is
barely mobilized before soil along the failure surface first reaches its peak shear strength.
When the average mobilization of soil shear strength along the potential failure surface
exceeds approximately 95% of its peak strength, the reinforcement tensions start to be
rapidly mobilized. Even so, when the average mobilization of soil strength reaches 100%
of its peak shear strength, still over 30% of average reinforcement strength has not yet
been mobilized. The results were used to explain important aspects of the current design
methods (i.e., earth pressure method and limit equilibrium analysis) that result in conservatively designed GRS structures. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/6659 |
| Date | 23 October 2009 |
| Creators | Yang, Kuo-hsin |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Format | electronic |
| Rights | Copyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works. |
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