|Principal Investigator(s) and Institution(s)
Geoffrey R. Martin, University of Southern California
The vulnerability of bridges to earthquake-induced liquefaction lateral
ground deformation (or spread) has been clearly demonstrated in past
earthquakes. Liquefaction mitigation options through soil remediation
have been addressee in several tasks previously conducted under the FHWA/MCEER
Highway Project DTFH61-92-C-00106. However, further research is needed
on mitigation options related to foundation design or retrofit as
current methods of soil improvement are very costly and time-consuming
to implement. A number of case histories and a limited number of
analyses have indicated that, with appropriate design, foundations can
accommodate relatively large ground deformation demands from lateral
The results from this study will establish: (1) practical
analysis approaches to evaluate the ability of foundation systems
normally associated with short to medium span bridges (pile footings and
drilled shafts) to accommodate displacement demands arising from lateral
spreads; (2) a case study database (including verification studies using
the above analysis approach) which will document field observations in
past earthquakes and results of centrifuge modeling simulations; and (3)
general design guidelines on conditions suitable for structural retrofit
or a structural mitigation option versus ground remediation solutions.
In Research Year 1, the following subtasks were accomplished:
comprehensive database was compiled documenting field case histories
where foundation systems had been subjected to lateral spreads, with
specific details on damage/no damage information. Test data and pile
performance arising from centrifuge model tests simulating the effects
of lateral spreads on pile foundations was also documented in the
- A summary report was prepared of analysis methodologies
presently available for evaluating the effects of soil-pile interaction
during liquefaction induced lateral spread. Most methods use p-y
interface spring models.
- The one-dimensional DESRA-MUSC nonlinear site
response computer program was modified to provide analysis tool for
determining the magnitude and distribution of earthquake induced
downslope permanent displacements in the time domain.
- A preliminary
evaluation of the use of the 3-D FLAC code (purchased as part of Task
C2-2) for studying soil-pile interaction during lateral spreads and for
calibrating simpler p-y interface models, was undertaken.
The scope of
the Year 2 research program is as follows:
- Emphasis will be placed on
developing a design oriented analytical model capable of simulating
soil-pile-structure interaction (and related impact on foundations and
the superstructure) during lateral spreads seated in a weak subsoil
layer. The model will be capable of including either drilled shaft or
pile group interaction (including a pile cap embedded in a soil crust),
the development of plastic hinges in pile members
or cap connections, and restraint arising from the bridge
superstructure. The latter effects have been shown to be important form
field case studies and centrifuge test results.
- To guide the
development of the analytical model, the 3D-FLAC program will be used to
study the mechanics of the problem (including pile group effects) and to
evaluate selected case histories. The case history evaluation will
initially focus on the 1987 Edgecumbe, NZ earthquake and the Landing
Road Bridge performance, together with existing RPI centrifuge test
data. Close collaboration will be maintained with the proposed new RPI
test program, which would provide valuable new insights on pile group
behavior at close pile spacing and on pile cap-crust interaction.
- Based on the FLAC results and the results of parameter studies using the
analytical model, recommendations will be made for design guidelines.
The model most likely will be based on the use of non-linear interface
springs for soil-foundation interaction simulation.
This model will then
form the basis for possible future studies encompassing large pile
groups (under the long-span bridge program) and possible future
parametric studies using structural codes to better accommodate the
structure-foundation interaction and to more closely simulate structural
vulnerability due to displacement demands.
08/01 Report describing analysis results and design guidelines
describing analysis approaches to assess pile foundation performance
under lateral spread displacement demands.