Modeling the Time-Dependent Behavior of Geosynthetically Reinforced Soil Structures with Cohesive Backfill - Reinforced Soil Engineering: Advances in Research and Practice - page 71

5 CHARACTERIZATION OF FOUNDATION SOIL
One advantage of reinforced soil structures over conventional ones is a tolerance
to deformations and stresses induced by yielding in the foundation. This allows
such structures to be constructed on less than ideal sites, with various types of
foundations. Depending on its stiffness, the foundation may have a significant
effect on the performance of the reinforced structure. When the foundation is soft,
the reinforcement will be affected by settlement of the underlying soil. If, on the
other hand, the foundation is quite stiff, its deformation will be negligible and
will not appreciably affect the behavior of the structure.
From the point of view of numerical analyses, a soft foundation has the
added potential of producing finite strains and rotations in the soil and
reinforcement. As a result, the analysis is complicated by the need to account for
not only material nonlinearities, but geometric ones as well. The associated
computational effort typically increases rather sharply.
6 SPATIAL DISCRETIZATION OF GEOSYNTHETIC
REINFORCEMENT
Since their inception, soil reinforcement techniques have employed many
different types of reinforcement. For the case of soil walls and embankments,
metal strips, geotextiles, and geogrids represent the primary types of
reinforcement. Such materials are quite thin and possess volume fractions
that, compared to the soil mass, are quite low. As a result, the bending
stiffness of the reinforcement is negligible; it is only the axial stiffness that
contributes to the behavior of a reinforced soil structure. In general,
geosynthetics are ductile materials; their strain at failure exceeds 10%.
Typically the reinforcement is modeled using one-dimensional bar (axial),
bending (axial-flexural), or large deformation “membrane” elements in which
transverse loading induces axial deformations. Nonlinearity of the stress-strain
behavior and yield can also be accounted for by making the element equations
functions of the stress or strain level.
In the case of mixed formulations, the reinforcement may also be used for
drainage. As such, the elements used to discretize the reinforcement must
complement displacements with pore pressure unknowns. The element
formulation can be semicoupled or uncoupled. In the former, the deformation
of the element affects the flow properties by reducing the area available for flow.
In the latter, the flow is independent of the element deformation.