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4.4.3 EPOLLS Model for Lateral Spread Displacement
The most recent model for estimating horizontal displacements is termed EPOLLS – Empirical
Prediction of Liquefaction-Induced Lateral Spreading (Rauch and Martin 2000). The model was
developed from a database of 71 historical lateral spreads using statistical regression techniques.
The model can be used to estimate the average horizontal displacement given site-specific
seismological, topographical, and geological parameters. The model has been formulated in three
complementary parts: (1) the Regional-EPOLLS component, designed for seismic hazard
surveys of geographic regions; (2) the Site-EPOLLS component, which gives improved
predictions for site-specific studies; and (3) the Geotechnical-EPOLLS component, which uses
additional data from subsurface explorations, thereby reducing uncertainty in the estimated
lateral spread displacement. An overview of the EPOLLS model and the predictive equations
used are shown in Figure 4.8. As with the method by Youd and others, this model should not be
applied for scenarios that are significantly different from those cases used to develop the
predictive equation.
4.5 ANALYTICAL METHODS FOR ESTIMATING LATERAL SPREAD
DISPLACEMENT
The empirical methods for estimating lateral spread displacement are straightforward tools for
preliminary hazard screening at bridge sites. Also, the empirical basis for the displacement
estimates provides credibility to these methods. The methods are, however, limited in their
application to the specific range of earthquakes, source-to-site distances, geological and
geotechnical conditions, and topographies from the cases studies employed in the development
of the predictive relationships. Most of the lateral spreads were evaluated at free-field sites.
These conditions severely limit the application of the empirical methods for bridge sites with
embankments and site-specific configurations. In these cases, the empirical approaches can be
used only as approximate indicators of lateral spread hazard, and supplementary analysis
procedures are required. Common methods of analysis include rigid body mechanics (i.e., the
sliding-block methods) and numerical effective stress modeling.
4.5.1 Newmark Sliding Block Model
In most applications involving waterfront slopes and embankments, it is necessary to estimate
the permanent slope deformations that may occur in response to the cyclic loading. Allowable
deformation limits for slopes will reflect the sensitivity of adjacent structures, foundations and
other facilities to these soil movements. Enhancements to traditional pseudostatic limit
equilibrium methods of embankment analysis have been developed to estimate deformations for
soils that do not lose appreciable strength during earthquake shaking (Makdisi and Seed 1978;
Ambraseys and Menu 1988; Jibson 1993). These methods are not appropriate for modeling flowtype
failures that can be associated with very loose saturated sands (N = 3-5 blows/ft).
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