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