TM 5-818-1 / AFM 88-3, Chap. 7
c. Permeability of rock.
Intact rock is
test results may also be plotted as change in volume
versus effective vertical stress. Typical examples of
generally impermeable, but completely intact rock
pressure - void ratio curves for insensitive and sensitive,
masses rarely occur. The permeability of rock masses is
normally loaded clays, and preconsolidated clays are
controlled by discontinuities (fissures, joints, cracks,
shown in figure 3-7.
etc.), and flow may be either laminar (Darcy's law
applies) or turbulent,
depending on the hydraulic
b. Preconsolidation
pressure.
The
gradient, size of flow path, channel roughness, and other
factors. Methods for determining the in situ permeability
preconsolidation stress, pc, is the maximum effective
of rock are presented in chapter 4.
stress to which the soil has been exposed and may
result from loading or drying. Geological evidence of
past loadings should be used to estimate the order of
3-5.
Consolidation. Consolidation is a time-de-
magnitude of preconsolidation stresses before laboratory
pendent phenomenon, which relates change that occurs
tests are performed.
The Casagrande method of
in the soil mass to the applied load.
obtaining
the
preconsolidation
pressure
from
consolidation tests is shown in figure 3-7. Determining
a. Consolidation test data. Consolidation or
the point of greatest curvature
one-dimensional compression tests are made in
accordance with accepted standards. Results of tests
(fig 3-6) are presented in terms of time-consolidation
curves and pressure-void ratio curves. The relationship
between void ratio and effective vertical stress, p, is
shown on a semilogarithmic diagram in figure 3-6. The
NOTE:
THE MINIMUM VOID RATIOS WERE OBTAINED FROM SIMPLE SHEAR TESTS. CURVES ARE
ONLY VALID FOR CLEAN SANDS WITH NORMAL TO MODERATELY SKEWED GRAIN-SIZED
DISTRIBUTIONS.
(Modified from ASTM STP 523 (pp 98-112). Copyright ASTM, 1916 Race St.,
Philadelphia, PA. 19103. Reprinted/adapted with permission.)
Figure 3-4. Generalized curves for estimating emax, and emin from gradational and particle shape characteristics.
3-5
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