Environmental Engineering Reference
In-Depth Information
NX drill hole with
REX-7P
Mortar pad
To pressure
apparatus
Pressure gage
Aluminum
bearing plate
REX - 7P cable
10" aluminum
tubing (25.4 cm)
Spacer plate
Center extensometer
Dial gage (Two-way
movement)
REX - 7P cable
FIGURE 3.71
Arrangement for uniaxial jacking test in
an adit. (From Wallace, B. et al., STP 477,
American Society for Testing &
Materials, Philadelphia, PA, 1970,
pp. 3-26. Reprinted with permission of
the American Society for Testing and
Materials.)
Adjustable screw
To pressure
recorder-
controller
To pressure
apparatus
Freyssi float jack
NX drill hole with REX - 7P
be used to determine stress distributions. The values for the modulus
E
are given in terms
of the test geometry, the applied pressure, the deflection, and Poisson's ratio.
Static moduli
are determined from plate-jack tests, radial jacking and pressure tunnel
tests, flat-jack tests, borehole tests (dynamometer and Goodman jack), and triaxial com-
pression tests.
Dynamic moduli
are determined from seismic direct velocity tests (see
Section 2.3.2)
and
the 3-D velocity probe (sonic logger) (see
Section 2.3.6).
Relationships between seismic
velocities and dynamic moduli are given in
Table 3.27
.
In moduli computations, the shear
wave velocity
V
s
is used rather than the compression-wave velocity
V
p
because water in
rock fractures does not affect
V
s
, whereas it couples the seismic energy across joint open-
ings, allowing much shorter travel times for P waves than if an air gap existed. Dynamic
moduli are always higher than static moduli because the seismic pulse is of short duration
and very low stress level, although the ratio of
E
static
to
E
d
will normally approach unity as
rock-mass quality approaches sound, intact rock.
E
d
as determined from field testing is
often referred to as
E
seis
and is correlated with other field and laboratory data to obtain a
design modulus, as will be discussed.
Plate-Jack Test (In Situ Compression Test)
Performance
A load is applied with hydraulic jacks to a plate in contact with the rock mass using the
roof of an adit as a reaction, as illustrated in Figure 3.71.
When the tests are set up, areas representative of rock-mass conditions are selected,
and the size of the loaded area is scaled to the structural elements of the rock. (Depending
on mass-defect spacings, the larger the loaded area the more representative are the
results). Borehole extensometers (see
Section 4.3.4)
are grouted into the rock mass for
