Geoscience Reference
In-Depth Information
Fig. 12.17. Transverse section of an abutment showing theequivalent tributarywidth
that isassumed to interact withtherestrainingforces from the pile foundation and
bridge superstructure
3.2.2. Estimating pile/bridge restraining forces for a range of displacements
The restraining forces from the pile foundation and bridge superstructure are estimated
for a range of possible embankment displacements. Inertia from the bridge structure
will alternate between causing an increase and decrease in the restraining force on the
embankment.Theequivalentstaticrepresentationofrestrainingforcesfromthepilefoun-
dation and bridge superstructureneglects thetransient influence of bridge inertiaforces.
The restraining force from the pile foundation is determined using an equivalent sta-
tic BNWF SD pushover analysis. In this analysis, the imposed soil displacements are
progressively increased and the shear forces and bending moments in the piles at the
location of the slope stability failure surface are determined. The ultimate shear force
that can develop will be limited by plastic hinging in the piles. The moment capacity of
the piles, and hence their shear resistance, may be further reduced by geometric effects
(i.e., P-
or buckling) as the abutment displacements become significant (Martin et al.,
2002).
The development of restraining forces from the bridge superstructure with increasing
embankmentdisplacementdependsonthestructuralconfigurationanddetails(e.g.,bear-
ings, expansion joints, shear capacity of seat abutment back wall) and the characteristics
of the embankment soils (e.g., passive resistance against an abutment back wall that is
designedtobreakawayduringdesignloading).Therestrainingforcethatdevelopsatthe
abutmentmustbetransferredtoeithertheintermediatebentsortotheoppositeabutment.
