(1) Sampling and laboratory testing. For

with respect to the external surface geometry and the

foundation soils, relatively undisturbed samples

distribution of materials in the embankment and

should be obtained. For embankment or backfill

underlying foundation. Additionally, the mesh should

materials, laboratory compacted specimens can be

reflect the configuration of any excavations or filling

prepared. In either case, the specimens should be

operations performed as part of construction. Most

tested in the laboratory in an appropriate manner to

embankment construction problems are either 2-D

obtain the necessary parameter values for the

plane-strain or 3-D type analyses. Levees or

material model that will be used. Typical

embankment dams constructed across broad alluvial

laboratory tests for obtaining these values are 1-D

valleys are good candidates for 2-D plane strain

consolidation tests, isotropic consolidation tests,

analysis, whereas embankment dams constructed

triaxial compression tests, and direct simple shear

within narrow canyons are good candidates for a 3-D

tests.

finite element analysis. The mesh should also extend

beyond the area of interest until a known boundary

(2) Field testing. Some *in situ *tests, e.g., the

condition is encountered (e.g., bedrock can often be

borehole pressuremeter tests can be performed to

represented as a fixed boundary condition) or for a

obtain material property values.

sufficient distance that conditions at the boundary do

not significantly influence the calculated stresses and

(3) Correlations with index property values.

deformations in the area of interest.

Stress-strain material property values for several

soils have been published together with index

property values for the same soils, e.g., Duncan et

model the construction sequence in embankment

al. (1980). These published values, together with

problems for two reasons:

judgment and experience, can be used to estimate

appropriate stress-strain material property values

(1) Soil response is nonlinear.

based on index property test results for the soils of

interest.

(2) Geometry can change during construction,

e.g., fill placement.

(4) Calibration studies. In many cases, designers

have experience with local soils and are skilled at

Because the nonlinear stress-strain behavior of soils

calculating 1-D consolidation settlements using

depends on the confining pressure, it is almost always

conventional procedures. It is good practice in such

necessary to first calculate the initial *in situ *stresses in

cases to develop a 1-D column of finite elements that

the foundation materials. Perhaps the only exception

models the soil profile at the site of interest. The 1-D

occurs when a rock foundation is being modeled as

column can be loaded and the resulting settlements

linear elastic. In addition, it is necessary to model the

compared to those calculated using conventional

following types of construction operations in steps:

procedures. The material property values for the finite

excavation, fill placement, placement and removal of

elment analyses can be adjusted until a match is

structural components, and application of loads and

obtained. Similarly, if an independent estimate of the

pressures. The construction steps should be modeled

lateral load response, i.e., the Poisson effect, can be

in the actual order in which they are to be carried out.

made, the material property values can be adjusted

until the 1-D column results match the independent

estimate. Ideally, one set of material property values

seen from the foregoing, there are several factors that

would be found that provides a match to both the

must be carefully considered to develop a good finite

compressiblity and the lateral load response over the

element model of an embankment construction

range of applied loads in the problem to be analyzed.

problem. It is important to successful application of

The selection of a method to obtain material property

the method over the years to calibrate the entire

values depends, of course, on the type of information

process against instrumented case histories.

available. These methods are most effective when

Fortunately, several such comparisons have been

used in combination.

published. Several of these are listed among the

references in Chapter 4.

should reflect the geometry of the embankment, both

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