Geoscience Reference
In-Depth Information
deformation should be analyzed separately by using procedures based on the sliding
block model to estimate deviatoric-induced displacements and using other procedures
(e.g., Tokimatsu and Seed, 1987) toestimate volumetric-induced seismic displacements.
The calculated seismic displacement from Newmark-type procedures, whether the pro-
cedure is simplified or advanced, is viewed appropriately as an index of seismic perfor-
mance. Seismic displacement estimates will always be approximate in nature due to the
complexities of the dynamic response of the earth/waste materials involved and the vari-
ability of the earthquake ground motion. However, when viewed as an index of potential
seismic performance, the calculated seismic displacement can and has been used effec-
tively in practice to evaluate earth/waste structuredesigns.
3. Components of a seismic displacement analysis
3.1. GENERAL
The critical components of a seismic displacement analysis are: (1) earthquake ground
motion,(2)dynamicresistanceofthestructure,and(3)dynamicresponseofthepotential
sliding mass. The earthquake ground motion is the most important of these components
intermsofitscontributiontothecalculationoftheamountofseismicdisplacement.The
variability in calculated seismic displacement is primarily controlled by the significant
variability in the earthquake ground motion, and it is relatively less affected by the vari-
ability in the earth slope properties (e.g., Yegian et al., 1991b; Kim and Sitar, 2003).
The dynamic resistance of the earth/waste structure is the next key component, and the
dynamic response of the potential sliding mass is generally third in importance. Other
factors, such as the method of analysis, topographic effects, etc., can be important for
somecases.However,thesethreecomponentsaremostimportantforamajorityofcases.
In critiquing various simplified seismic displacement procedures it is useful to compare
how each method characterizes the earthquake ground motion and the earth/waste struc-
ture's dynamic resistanceand dynamic response.
3.2. EARTHQUAKE GROUND MOTION
An acceleration-time history provides a complete definition of one of the many possi-
ble earthquake ground motions at a site. Simplified parameters such as the peak ground
acceleration (
PGA
), mean period
maybeused
in simplified procedures to characterize the intensity, frequency content, and duration,
respectively, of an acceleration-time history. Preferably, all three, and at least two, of
thesesimplifiedgroundmotionparametersshouldbeused.Itisoverlysimplistictochar-
acterize an earthquake ground motion by just its
PGA
, because ground motions with
identical
PGA
values can vary significantly in terms of frequency content and duration,
and most importantly in terms of its effects on slope instability. Hence,
PGA
is typi-
cally supplemented by additional parameters characterizing the frequency content and
duration of the ground motion. For example, Makdisi and Seed (1978) use earthquake
(
T
m
)
, and significant duration
(
D
5
-
95
)
