Liquefaction Effects

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Participants

		PhD Student Researcher Shideh Dashti BS Civil Engineering, Cornell University MS GeoEngineering, UC Berkeley

		Principal Investigator Professor Jonathan D. Bray Professor of GeoEngineering, UC Berkeley

		UC Berkeley Technical Staff Dr. Michael F. Riemer Associate Adjunct Professor, UC Berkeley

		UC Davis Technical Staff Dr. Dan Wilson Research Engineer, UC Davis UC Davis Center for Geotechnical Modeling Facility Manager

		Undergraduate Assistant Wing Shun Kwan UC Berkeley

		Sponsor National Science Foundation (NSF)
Papers: NEES 5th Annual Conference in Snowbird, Utah, June 2007 "This material is based upon work supported by the National Science Foundation under Grant No. CMS-0530714. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. This project was also partially supported by the NSF through the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES)."

Background

Recent earthquakes such as the August 17, 1999 Kocaeli Earthquake, have provided countless examples of the damaging effects of liquefaction. Observations of building performance include punching/settlement, bearing failure, and lateral shifting of buildings. Many of these structures were affected by ground failure due to liquefaction of shallow silt deposits where the occurrence of structural damage was found to be related to the occurrence of ground failure.

99 Kocaeli
Source: Bray et al. 2004

Source: Sancio & Bray 2004

Source: GEER

Soil-foundation-structure-interaction(SFSI) plays a significant role in soil response and structure performance when ground softening occurs. Detailed documentation of the sequence of liquefaction, ground failure, and the resulting impacts on the performance of the structures is generally not available at key sites that have been affected by ground softening. Therefore, the connections between ground response and building response are not well understood. This is a necessary yet missing step in the development of advanced soil response models and building performance analytical procedures.

Research Objectives

Although much can be learned through investigating field case histories, advancements are often hampered due to the significant uncertainties involved. Properly scaled centrifuge model experiments under controlled laboratory conditions that mimic those in heavily damaged areas provide an excellent opportunity to observe the effects of soil liquefaction on building performance.

RESEARCH GOALS:

To move past the prediction of free field liquefaction to the next level: the ability to predict deformations for structures by considering the timing, sequence, and location of soil strength loss near constructed facilities.
To explore the relative importance of the thickness of the liquefiable soil layer and its void ratio, while examining the interacting effects of different buildings and foundation conditions on the response of the liquefiable soils and building performance.
To investigate the relation of ground failure due to silt compared to that for clean sand, which is relatively better understood.
To obtain illustrative model studies which will offer emergency managers and teachers a dramatic alternative to currently existing static pictures of tilted buildings.

MEANS:

Generation of 12 well-documented "case histories" of building response on liquefied ground, using the UC Davis large centrifuge. In the small-scale centrifuge test series, the input motion, surface motion, ground conditions, ground response, and structural response are carefully documented.
Numerical analyses to back-analyze the results of the centrifuge tests (using the fully-nonlinear SFSI program OpenSee), which will enhance our understanding of ground failure and its resulting impacts on structures.