b. Index Properties Tests. Index properties are used to classify
soils, to group soils in major strata, to obtain estimates of structural
properties (see correlations in this Chapter), and to correlate the results
of structural properties tests on one portion of a stratum with other
portions of that stratum or other similar deposits where only index test
data are available. Procedures for most index tests are standardized (Table
1). Either representative disturbed or undisturbed samples are utilized.
Tests are assigned after review of boring data and visual identification of
samples recovered. For a simple project with 4 to 6 borings, at least 3
gradation and/or Atterberg tests should be made per significant stratum (5
to 15 feet thick). For complex soil conditions, thick strata, or larger
sites with more borings, additional tests should be made. Moisture content
tests should be made liberally on samples of fine-grained soil. In general,
the test program should be planned so that soil properties and their
variation can be defined adequately for the lateral and vertical extent of
the project concerned.
c. Tests for Corrosivity. The likelihood of soil adversely affecting
foundation elements or utilities (concrete and metal elements) can be
evaluated on a preliminary basis from the results of the tests referenced in
Table 1. The tests should be run on samples of soil which will be in
contact with the foundations and/or utilities in question; typically these
will be only near-surface materials. For a simple project with uniform
conditions, three sets of tests may be adequate. Usually the chemical tests
are run only if there is reason to suspect the presence of those ions. (See
DM-5.7 for application of test results and possible mitigating measures.)
d. Structural Properties Tests. These must be planned for particular
design problems. Rigid standardization of test programs is inappropriate.
Perform tests only on undisturbed samples obtained as specified in Chapter 2
or on compacted specimens prepared by standard procedures. In certain
cases, completely remolded samples are utilized to estimate the effect of
disturance. Plan tests to determine typical properties of major strata
rather than arbitrarily distributing tests in proportion to the number of
undisturbed samples obtained. A limited number of high quality tests on
carefully selected representative undisturbed samples is preferred. In
general, selecting design values requires at least three test values for
simple situations of limited areal extent; larger and more complex
conditions require several times these numbers.
Where instantaneous deformation characteristics of soils are to be
evaluated, constitutive relationships of the materials in question must also
be established. For initial estimates of Young's modulus, E+s,, see Chapter
5, and for K+o, value, see DM-7.2, Chapter 3.
e. Dynamic Tests. Dynamic testing of soil and rock involves three
ranges: low frequency (generally less than 10 hertz) cyclic testing,
resonant column high frequency testing, and ultrasonic pulse testing. The
dynamic tests are used to evaluate foundation support characteristics under
repeated loadings such as a drop forge, traffic, or earthquake; a primary
concern is often liquefaction. Young's modulus (E+s,), shear modulus (G),
and damping characteristics are determined by cyclic triaxial and simple
shear tests. Resonant column can be used to determine E+s,, G, and damping.