Environmental Engineering Reference
In-Depth Information
Figure 12.13.
Contractive (a) and dilatent (b) soils in undrained static and cyclic loading.
using S
us
in the liquefied soil. If it is significantly less than 1.0, large, rapid deformations
will occur based simply on the momentum effects.
12.4.1.3
Suggested flow chart for evaluation of soil liquefaction
Robertson (1994) and Robertson and Wride (1997) suggest that the flow chart shown in
Figure 12.14
be used for the evaluation of soil liquefaction. The following summary of the
conditions for flow liquefaction, cyclic liquefaction and cyclic mobility is taken from
those papers:
(a)
Flow liquefaction
- Applies to strain softening soils only;
- Requires a strain softening response in undrained loading resulting in constant
shear stress and effective stress;
- Requires in-situ shear stresses greater than the ultimate or minimum undrained
shear strength, as illustrated in Figure 12.13;
- Either monotonic or cyclic loading can trigger flow liquefaction;
- For failure of a soil structure to occur, such as a slope, a sufficient volume of mate-
rial must strain soften. The resulting failure can be a slide or a flow depending on
the material characteristics and ground geometry. The resulting movements are due
to internal causes and can occur after the trigger mechanism occurs;
- Can occur in any metastable saturated soil, such as very loose granular deposits,
very sensitive clays, and loess (silt) deposits.
