Measurement of Properties - Geotechnical Engineering Investigation - page 250

Embankment Tests
Embankments are constructed to obtain information on the compressibility of loose fills,
or thick deposits of soft clays and weak organic soils, and are often designed to preload
weak soils. An embankment with height and width, adequate to stress the weak soils to a
substantial depth, is constructed with earth fill. Instrumentation is installed to monitor
deflections and pore pressures as functions of time (see Section 4.5.2). Interpretation of the
field data and correlations with laboratory test data provide information on the magnitude
and time rate of settlements to be anticipated, as well as on the height limitations during
actual construction required to avoid shear failures. This is the most reliable procedure for
evaluating the characteristics of weak organic deposits.

3.5.5 Dynamic Deformation Moduli (Soils)

Methods Summarized
Laboratory Methods
Dynamic deformation moduli are measured in the laboratory in the cyclic triaxial and
cyclic simple shear (see Section 3.4.4) , and cyclic torsion, ultrasonic, and resonant column
devices as summarized in Table 3.33.
To date, the shaking table test has been used primarily in university research studies and
is described in Novacs et al. (1971) and De Alba et al. (1976). Dynamic testing procedures
are described in detail in USAEC (1972).

In Situ Methods
Dynamic moduli are measured in the field by seismic direct methods and steady-state
vibration methods. Vibration monitors obtain data on ground motion (see Section 4.2.5).

Resonant Column Devices
Apparatus
Several types are in use as described in USAEC (1972).

Procedure
The specimen is placed in a chamber, subjected to a confining pressure stimulating over-
burden pressure, vibrated first in the torsional mode and then in the longitudinal mode,
while end displacements are monitored.
Shear-wave velocity is computed from the torsional test results and the compression-
wave velocity from the longitudinal test results as functions of specimen and end dis-
placements. Dynamic Young's modulus E d and dynamic shear modulus G d are computed
from equations given in Table 3.27. When applicable, factors are applied to include the
effects of damping and end conditions during test.
See also ASTM D4015-92(2000).

Seismic Direct Methods
Purpose
As described in Section 2.3.2, seismic direct methods are used to obtain values of E d and
G d , and have been used for estimating values of E s in medium-dense to dense sands for
settlement computations where small strains are critical.