Geoscience Reference
In-Depth Information
Fig. 12.19. Compatibility between the computed embankment slide massdisplacements
and the equivalent constant restrainingforce from the pile foundation
These and other results suggest that the recommended pinning analysis procedures pro-
vide a reasonable design approach for estimating the relative effect that pinning forces
can have on embankment displacements. Despite the approximations and uncertainties
involved,themethodologycanbeusedtobrackettherangeoflikelypinningeffectswith
sufficient accuracy for decision making in many situations. In other situations, dynamic
numericalanalysesmayprovideinsightsintothesystemresponsecharacteristicsthatare
valuable enough to warrant the additional engineering costs. For either analysis method,
the final design must account for the significant uncertainties involved in predicting
liquefaction-induced ground displacements, as previously discussed forlateral spreads.
4. Other issues and considerations
The response of the global bridge system for the liquefaction case needs to be evalu-
ated after the individual bents and abutments have been evaluated as local systems. A
dynamic analysis of the global bridge system is often performed for the nonliquefac-
tion case (e.g., Caltrans, 2006), in which the soil is often represented by spring elements
attached to the structure model. A dynamic analysis of the global bridge system for the
liquefaction case is far more complicated because the inclusion of dynamic ground dis-
placements requires some type of continuum modeling for the soil profile. Alternatively,
an equivalent static analysis of the global bridge system for the liquefaction case may be
performed wherein a number of different possible loading combinations would need to
be considered; for example, liquefaction effects at one or more locations in combination
withinertiademandsindifferentdirections.Thedevelopmentofimprovedguidelinesfor
analysesofglobalbridgesystemsfortheliquefactioncaseisanareaofongoingresearch.
