MCEER HIGHWAY PROJECT
FHWA CONTRACT DTFH61-98-C-00094

Seismic Vulnerability of the Highway System

Task E1-2: Foundation Design for Liquefaction-Induced Lateral Displacements

Subject Area: Geotechnical and Foundation Engineering 
Research Year 2

Principal Investigator(s) and Institution(s)

Geoffrey R. Martin, University of Southern California

Objective

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 spreads.

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.

Approach

In Research Year 1, the following subtasks were accomplished:

  1. A 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 database.

  2. 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.

  3. 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.

  4. 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:

  1. 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.

  2. 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.

  3. 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.
  

Products

08/01 Report describing analysis results and design guidelines describing analysis approaches to assess pile foundation performance under lateral spread displacement demands.

8/14/01

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