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A second, and more elegant, way of analyzing such problems is to look at
the domains in their entirety. More precisely, the portion of the domain in which
the response is of interest is discretized using standard finite elements. Along the
boundary, the domain is represented by so-called 'infinite' elements, which were
first proposed by Bettess (1977). During the last 20 years, a number of authors
have refined this element type (Bettess, 1980; Curnier, 1983; Zienkiewicz et al.,
1983; Marques and Owen, 1984; El-Esnawy et al., 1995), so that today analysts
can make use of this procedure for static and dynamic analyses in a
straightforward manner. One big advantage of this method is that it merely
implies an addition to the element library of the finite-element code being used
and yet allows for an accurate representation of semi-infinite half-spaces. The
application of “infinite” elements to the modeling and analysis of geotechnical
problems was recently studied by Fuchs (1999) and Dechasakulsom (2000), who
critically assessed the advantages and drawbacks of such an approach.
4 CHARACTERIZATION OF COHESIVE BACKFILL
In mathematically modeling the cohesive soil retained by the geosynthetically
reinforced soil structure, it is important to account for its time dependence. This is
best realized by characterizing the soil as an elasto-viscoplastic continuum. From
a practical point of view, the analysis is complicated by the need to account for
material nonlinearities.
Many constitutive models have been proposed that can provide a time-
dependent material characterization. The two general types of models are
elastic-viscoplastic (Adachi and Oka, 1982; Nova, 1982; Sekiguchi, 1984;
Borja and Kavazanjian, 1985; Oka, 1985) and coupled elastoplastic-
viscoplastic (Kaliakin and Dafalias, 1990) based formulations. Further details
pertaining to such models are beyond the scope of this paper. The interested
reader is directed to the above references and to the state-of-the-art review of
Adachi et al. (Adachi et al., 1996).
While there is no question that modeling cohesive soils in a time-dependent
manner is a correct and rational approach, it is timely to note that a rather large
number of past analyses of geosynthetically reinforced soil structures involving
such soils has instead employed time-independent models. These have typically
been variants of the quasi-linear elastic (“hyperbolic”) idealization of Duncan
and Chang (1970). While such models are quite easy to implement, recent
numerical studies (Dechasakulsom, 2000) have shown their use to be quite
inaccurate at best.
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