Department of Civil Engineering

National Institute of Technology Calicut

SEMINAR

THE SEISMIC RESPONSE OF BRIDGE PILE FOUNDATIONS

TO LIQUEFACTION INDUCED LATERAL SPREADING

Abstract

Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by

seismicity or other rapid loading. During liquefaction, the saturated and unconsolidated soil

behaves like a liquid of negligible shear strength. The failure mechanisms during liquefaction

include lateral spreading, loss of bearing capacity, settlement of abutments, ground oscillations

and flow failure.

The liquefaction-induced lateral spreading has caused major damage to bridge structures

during past earthquakes. Lateral spreading consists of the displacement of ground down the gentle

slopes or towards an incised channel due to dynamic or gravitational forces, as a result of

liquefaction of underlying soils. Lateral spreading cause large lateral deformations at the

abutments ranging from a few centimeters to several meters, which may induce enormous forces

in the foundation, superstructure, and connections, leading to severe damage or even the collapse

of bridge structures.

The most influential parameters of lateral spreading are dynamic histories of acceleration

of the sliding soil mass, pore water pressure and pile bending moments. Earthquake-induced

deformation of piled bridge abutments in approach embankments underlain by liquefied soils may

be reduced by restraining the forces provided by the piles and bridge superstructure, i.e., by pile

pinning techniques. Other liquefaction mitigation techniques at existing bridges include

densification, cementation, reinforcement and containment, in-situ stress enhancement, and

drainage.

The possible failure modes that may occur in pile foundations, depends on the conditions

of fixity, pile reinforcement and ductility. Generally, if concrete piles were well embedded in the

pile caps, shear or flexural cracks occurred at pile heads, often leading to failure; if steel pipe piles

were fixed tightly in the pile caps, failure was at the connection or pile cap; or if the pile heads

were loosely connected to the pile caps, they either rotated or were detached.

Well-documented case studies are presented in detail to illustrate the performance of

bridges and their typical damage associated with lateral spreading. Design examples of several

bridges supported by various types of pile foundations are also presented and the pile response in

terms of plastic hinge development, pile ductility ratio and pile curvature response are studied.

The mechanisms of pile pinning and pile ductility fundamentally alter the design

methodologies for the earthquake response of bridge pile foundations to liquefaction induced

lateral spreading. The role of pile pinning in potentially reducing the displacement demands on the

bridge foundation is significant and pile ductility allows the pile to undergo greater displacement

without structural collapse. Pile plastic curvature capacity specific to a pile type can be evaluated

using accepted modeling procedures. By allowing the piles to form a plastic hinge and to mobilize

ductility, less earthquake displacement demand is transferred up to the bridge columns and

superstructure.

References

1) Zhang, J., Huo, Y., Brandenberg, S., and Kashighandi, P. (2008). "Effects of structural

characterizations on fragility functions of bridges subject to seismic shaking and lateral

spreading." Earthquake Engineering and Engineering Vibration, 10.1007/s11803-008-

1009-2, 369-382.

2) Armstrong, R., Boulanger, R., and Beaty, M. (2012). "Liquefaction Effects on Piled Bridge

Abutments: Centrifuge Tests and Numerical Analyses." Journal of Geotechnical and

Geoenvironmental Engineering, 10.1061/ (ASCE) GT.1943-5606.0000780, 433-443.

Submitted by,

ANJU B SUNIL

B120732CE

A BATCH, VIIth Semester