Soil Behavior: Dynamic Soil-Structure Interactions - Dynamic Behavior of Concrete and Seismic Engineering - page 131

Figure 4.4. Volume variations under cyclic loading

4.2. Modeling soil behavior

An exhaustive description of soil behavior can be obtained from a state of
balance, characterized by a stress field V and a strain state (characterized by tensor
H

), if it is possible to determine the stress field (or the new strain state)

corresponding to the new state of balance after applying strain increment d H (or
respectively of a stress increment d V ). In most cases, time also plays a part in the
expression of behavior law, but as a rule, for most soils, this parameter can be
neglected. Establishing the behavior law is the ultimate goal of the description of the
soil behavior. Nevertheless, because of the complexity of the experimental behavior
of the soil, establishing a true behavior law is both delicate and costly. At present, no
universal behavior law exists: each law available in literature has advantages as well
as drawbacks and limitations.

When confronted with these difficulties, geotechnicians often prefer to use
procedures commonly employed in soil mechanics, which involve anticipating the
stress mode to which an element isolated inside the soil layer will be subjected and
reproducing the corresponding loading path, either inside a sample or in situ . The
parameters measured during the test can then be used directly for the calculations.
For example, a similar approach is used in soil mechanics to study the subsidence of
a compressible clay layer due to the weight of a backfill, the extension of which is
important relative to the layer thickness: the test used would be an oedometric test
with no radial strain.

We have to realize that such an approach is not the same as determining a
behavior law, even if the stress-strain curves obtained are represented by
mathematical equations. This modeling of soil behavior is only valid for loading