Environmental Engineering Reference
In-Depth Information
Measurement of Values
Laboratory tests are used to measure the variation in shear modulus and damping as a
function of stress-strain amplitude up to levels of strong motion interest (see Sections 3.4.4
and 3.5.5).
In situ or field tests (see Section 3.5.5) take the form of direct-wave seismic surveys (see
Section 2.3.2), which provide compression and shear-wave velocities from which G and
other dynamic properties are computed. Because the moduli are obtained at lower ampli-
tudes than those imposed by earthquakes, they are likely to be somewhat higher than real-
ity. Values obtained from in situ testing are scaled down by comparing the results with
those obtained for the same soils from laboratory testing. Approximate strain ranges for
earthquake laboratory and field tests are compared in Figure 11.32.
A recent discussion of dynamic soil behavior and testing is found in Brandes (2003).
Evaluation of Data
The evaluation of shear modulus and damping ratio data is described in USAEC (1972)
and Hardin and Drenvich (1972a, 1972b).
Applications to soil-structure interaction (SSI) problems are discussed in Section 11.4.5.
Geophysical
Surface vibrator
Vibratory
plate bearing
Static
plate bearing
SM-EQ a
Earthquakes a
10 5
10 4
10 3
10 2
10 1
1
10
Shear strain
(%)
(a)
Cyclic triaxial
Cyclic simple shear
Torsional shear
Resonant column
S hake
table
SM-EQ a
Earthquakes a
10 5
10 4
10 3
10 2
10 1
1
10
Shear strain (%)
(b)
FIGURE 11.32
Comparison of approximate strain ranges for earthquakes, field and laboratory testing: (a) field tests and
(b) laboratory tests. (From USAEC, Soil Behavior Under Earthquake Loading Conditions, National Technical
Information Service TID-25953, U.S. Department of Commerce, Oak Ridge National Laboratory, Oak Ridge,
Tennesse, January 1972.)
a Range of shear strain denoted as “earthquake” represents an extreme range for most earthquakes. “SM-EQ”
denotes strains induced by strong-motion earthquakes.
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