Environmental Engineering Reference
In-Depth Information
2.0
1.5
∆
u
13
95
13
1
CYCLE
21
17
1.0
0.5
0
1.0
2.0
3.0
4.0
5.0
6.0
0.5
p, kg/cm
2
1.0
1.5
2.0
Figure 12.10.
Example of effective and total stress paths leading to cyclic liquefaction for isotropically
consolidated fine sand in a cyclic triaxial test (Hedberg, 1977; USNRC, 1985).
1.00
1000
300
3000
0.75
CYCLE No. 8900
0.50
0.25
0
0
0.5
1.0
1.5
2.0
2.5
p, kg/cm
2
Figure 12.11.
Example of effective and total stress paths leading to cyclic mobility on anisotropically
consolidated fine sand during cyclic triaxial compression test (Hedberg, 1977; USNRC,
1985).
If the sample is subjected to anisotropic consolidation, or to a constant shear stress
over and above the cycled stress, the stress paths are altered significantly, as shown in
Figure 12.11.
Here the cycling takes the sample from the failure line (compression side) away to a non-
failure condition so, while the soil will continue to strain, the continuous
0 condition
is not reached. This would be a cyclic mobility condition.
Laboratory tests show that the number of cycles to cause initial liquefaction is depend-
ent on the cyclic stress ratio
o
, the relative density (or void ratio related to the ultimate
state void ratio) soil particle size and fabric, the stress conditions, and stress path.
Figure
12.12
shows some tests on sand showing the effect of relative density and cyclic stress
ratio.
It will be noted that for a given cyclic stress ratio, soils at lower relative density require
fewer cycles of loading to achieve initial liquefaction.
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