Environmental Engineering Reference
In-Depth Information
Load vs. Compression Characteristics
Under normal loading conditions, compression in quartz sands is essentially plastic and
results from void closure. Compression of individual grains is insignificant except for
sands composed of soft materials such as shell fragments, gypsum, or lightly cemented
calcareous sands.
Compression magnitude in quartz sands is related to
D
R
, gradation characteristics, and
the magnitude of applied static load or the characteristics of dynamic loadings. A family
of curves representing pressure vs. void ratio for various values of
D
R
obtained by testing
reconstituted samples in a consolidometer, is given in
Figure 3.85.
Compression vs. Time
Compression under applied load results in the immediate closure of the voids as the
grains compact, although in saturated silty soils some time delay will occur as pore pres-
sures dissipate. The normal process of consolidation, however, does not occur. Swiger
(1974) reports a case where primary settlements occurred within 1 h of load application
during large-scale field load tests, but secondary compression, ultimately as large as pri-
mary compression, continued over a period of several years (see
Section 3.5.5)
.
Pressuremeter Testing
General
Pressuremeters are used for
in situ
measurements of deformation moduli and strength.
There are several types:
Menard pressuremeter for soils and soft rock (ASTM D4719)
●
Camkometer for soils
●
Dynamometer and Goodman jack for rock (see
Section 3.5.3)
●
Menard Pressuremeter
See Menard (1963, 1965, 1975), CGS (1978), and Terzaghi et al. (1996).
0
Interpolated compression by
relative density relations
0.9
Loose
28
0.8
Primary
loading
4
45
Unloading
47
0.7
6
70
6
70
0.6
FIGURE 3.85
Pressure-void ratio curves and relative
density relationships for a “coarse to fine
sand, little silt.” (From Burmister, D. M.,
ASTM, Vol. 48, Philadelphia, PA, 1948.
Reprinted with permission of the
American Society for Testing and
Materials.)
8
86
9
91
0.5
9
100
105
100
Dense
100
0
1/41/2
1
2
3
4
Consolidation pressure, in tons per sq. ft.
