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Proceedings of the 8th US-Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures Against Liquefaction

 

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Working Group Reports

Design, Mitigation and Rehabilitation of Lifeline Systems Against Earthquakes

  1. Develop empirical Multi-Linear Regression (MLR) permanent ground deformation analysis for clays.
  2. Develop simplified seismic models for lifeline performance.
  3. Develop models for transverse soil/pipe interaction for large permanent ground deformation using a conservative bilinear spring model.
  4. Develop models for longitudinal soil/pipe interaction for large permanent ground deformation using a conservative bilinear spring model.
  5. Provide information transfer to end users and policy makers, using proceedings, user workshops and executive summaries.
  6. Encourage discussion of technical differences on needed research.
  7. Contrast and critique current standards of practice versus research findings.
  8. Research faulting effect on lifelines.
  9. Instrument pipes to monitor their response
  10. Develop simplified analysis of liquefaction stages for evaluating the effect to lifeline structures including the pre, post and transient phase and dynamic response.
  11. Improve capability for predicting small to moderate transient and permanent ground movement less than 2 m and their consequences.
  12. Perform current design analysis on lifeline foundations having successful performances under extreme seismic conditions.
  13. Integrate research knowledge from this and other workshops to improve lifeline system performance evaluations.
  14. Evaluate most recent lifeline design guidelines with recent research results.
  15. Develop design guidelines for fire following earthquakes.
  16. Expand invitation to future US/Japan Workshops to other disciplines.
  17. Incorporate performance based design in research activities where applicable.

Ll 01-20-03 REV 020203

Liquefaction, Lateral Spreads, Fault Ruptures, and Permanent Ground Deformation Effects on Structures

Reporters:
J. P. Bardet, S. Ashford, K. Konagai, and T. Sato

Participants:
J. Stewart, B. Kutter, T. Abdoun, Y. Takahashi, T. L. Holzer, I. M. Idriss, K. Wakamatsu, O. Aydan

During the 8th US-Japan workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures against Liquefaction, a two-hour session was convened on December 18, 2003 on the topic of “Liquefaction, lateral spread, fault rupture, and permanent ground deformation effects on structures.” The session was attended by 12 workshop participants, including 4 reporters. The main objective of the session was to identify major research issues and needs on liquefaction and surface faulting and their effects on civil infrastructures. The session focused on three major topics:

  • Post-earthquake field surveys
  • Damage assessment due to liquefaction
  • Faulting and its effects on civil infrastructures

Post-earthquake field surveys
Earthquakes provide unique learning opportunities for earthquake engineers. Engineers tend to emphasize investigations of domestic earthquakes because their primary need is to evaluate the performance of structures built to standards and according to practices developed in their own country. Foreign earthquakes, however, often provide special opportunities to validate models and to learn about the performance of specific aspects of the built and natural environments that have implications for risk mitigation in their home country. The workshop recognized that a protocol is needed to facilitate post-earthquake investigations of earthquakes in the United States and Japan by investigators from the non-impacted country. Currently, most visits rely heavily on pre-established personal and professional relationships. The United States National Earthquake Hazards Reduction Program recently has established a plan to coordinate post-earthquake investigations (Holzer et al. 2003). The plan includes a process to accommodate visits by foreign scientists and engineers. The Workshop recommends that NSF remind investigating parties that it supports to follow this process. While the plan emphasizes coordination of investigations of domestic earthquakes, it presents a limited process for coordination of investigations of foreign earthquakes by U.S. investigators. The workshop recommends that NEHRP agencies that support investigations of foreign earthquakes review the process by which they provide support for the purpose of better coordinating their investigations and enhancing the availability of data collected by their investigators. This review should include consideration of the feasibility of making products from U.S. military resources available to investigators.

Post-earthquake investigations yield critical information for improving building codes. Until now, the information collected from post-earthquake surveys has been largely qualitative, with limited quantitative measurements. In view of the advances in remote sensing technologies and portable computers, post-earthquake surveys will yield even more valuable information to research and engineering practice if they were complemented with quantitative measurements performed in the days and weeks after the events. Post-earthquake measurements have become tractable thanks to the development of modern technologies, e.g., accurate global positioning systems (GPS) devices and portable electronic equipments.

Many damage survey technologies that have originated in the military sector may greatly benefit to post-earthquake reconnaissances. For instance, the remote sensing of structural damage, initially developed for assessing weapon impacts, could be useful to estimate rapidly the extent and location of earthquake damage in urbanized areas. It is recommended to establish communication channels with the U.S. Department of Defense to identify the military satellite technologies that are likely to improve rapid damage assessment after having migrated into the civilian sector.

The success of post-earthquake surveys depends on the availability of relevant support data, e.g. high-resolution topographic maps and aerial photographs. At the present, the collection and compilation of relevant maps and aerial photographs are usually performed just after the earthquakes by independent reconnaissance teams. It is recommended to create support websites that identify the sources of maps and aerial photographs in seismic prone areas before the events actually occur. Maps should be available digitally in geographic information systems (GIS) compatible format for easily reporting GPS observations.

Post-earthquake surveys document the evidences rapidly erased by man-made interventions (e.g. cleanup of rubbles and debris, and repair to damaged structures) and natural events (e.g., sand boils erased by rain). Post-earthquake surveys identify new study areas, which need to be later investigated in greater details through follow-up studies in the months after the earthquakes. A successful example of post-event studies is ROSRINE, which stands for ResOlution of Site Response Investigation from the Northridge Earthquake. Post-earthquake surveys only benefit to research and engineering practice if they are complemented with additional in-depth follow-up investigations aimed at implementing our new findings into engineering practice and building codes.

Surveys of damage assessment due to liquefaction
Post-earthquake surveys have identified liquefaction-induced ground deformation as a major source of earthquake damage. Post-earthquake measurements of liquefaction-induced ground deformation are desirable to understand better the relations between ground deformation and damage to civil infrastructure, and to construct fragility curves for a probabilistic assessment of liquefaction hazards. It is recommended to develop guidelines for post earthquake reconnaissance that document the utilization of modern portable GPS technologies and quantitative field survey GIS database.

Most of the case histories of liquefaction-induced ground deformation have been documented using aerial photographs before and after the events, which have typically yielded ground displacement accurate to 50 cm. The main limitation in processing aerial photographs is the availability of photographs prior to the earthquakes. It is recommended to document a few selected sites using high-resolution low-altitude aerial photographs and laser altimetry (e.g., LIDAR). It is also recommended to complement these remote sensing measurements with field measurements. To this effect, sites of interest need to be instrumented with monuments and inclinometers before the events. A possible way to characterize the extents and severity of liquefaction is to identify changes in fundamental site period using deployable seismic instruments, shortly after the earthquakes. Post-earthquake surveys should not only focus on the sites that display evidence of ground deformation, but should also identify areas with no perceptible ground deformation. There is a lot to learn by comparing the areas that liquefied and did not liquefy.

Faulting and its effects on the built environment
In the aftermath of earthquakes, the surface expressions of faults that ruptured at depth are usually mapped by geologists to understand the mechanisms of fault ruptures. This mapping has yielded valuable information on the rupture types (e.g., strike slip, thrust, and step-over), slip rates and recurrences of earthquakes. The devastating effects of surface faulting was recognized in the past 1971 San Fernando, and prompted the Alquist-Priolo Act which requires all inhabitable structures in California to be built at some distance away from active faults. The 1999 earthquakes in Turkey and Taiwan have shown that surface faulting threaten not only distributed lifeline networks but also buildings and structures, e.g. bridges. There are still unanswered questions about the relation between diffused ground strains and concentrated displacements where surface faulting display complicated geometries, e.g., stepovers. It is recommended to map surface faulting more quantitatively with measurement of distributed and localized ground deformations. From the point of view of solid mechanics, surface faulting may be difficult to describe deterministically because it is governed by material instability in soil deposits, the material properties and geometries of which are not well characterized. From an engineering point of view, it is recommended that future investigations establish databases of ground deformation and surface faulting with the intent of developing statistical models of ground deformation induced by surface faulting.

References

Holzer, T.L., Borcherdt, R.D., Comartin, C.D., Hanson, R.D., Scawthorn, C.R., Tierney, K, Youd, T.L., 2003, “The plan to coordinate NEHRP post-earthquake investigations,” U.S. Geological Survey Circular 1242, 16 p.

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