Location

San Diego, California

Session Start Date

5-24-2010

Session End Date

5-29-2010

Abstract

Although there exist some consensus regarding seismic soil liquefaction triggering assessment of free field soil sites, estimating the liquefaction triggering potential beneath building foundations still stays as a controversial and a difficult issue. Assessing liquefaction triggering potential under building foundations requires the estimation of cyclic and static stress state of the soil medium. In the recent studies (e.g. Unutmaz 2008), the cyclic stress ratio corrected for Kα and Kσ effects under and adjacent to building foundations subjected to cyclic loading are to be estimated with the help of a series of 2-D and 3-D numerical simulations for different generic cases. A representative and a maximum cyclic stress ratio terms of the soil-structure-earthquake interaction system, denoted as CSRSSEI,rep and CSRSSEI,max respectively was defined as a function of i) ratio of the pre-earthquake fundamental period of the structure and soil (σ), ii) free field spectral acceleration at the fixed-base period of the structure(SA), iii) the peak ground acceleration of the free field soil sites (PGA), and iv) aspect ratio of the structure (h/B). In this paper, the results of the previously mentioned numerical findings have been verified by using case histories documented after 1999 Kocaeli Earthquake, where significant foundation displacements were observed due to liquefaction of the underlying foundation soils. The foundation soil profiles of these case histories generally consist of silty soils, sand-silt mixtures and silt-clay mixtures. Overburden and procedure corrected SPT-N values vary in the range of 2 to 5 blows/30 cm in the upper 5 meters and gradually increases up to a maximum value of 25 blows/30 cm beyond depths of 5 to 8 m’s. Overlying structures are mainly 3 to 4 storey, residential buildings with no basements. As the concluding remark, the proposed simplified procedures are shown to predict cyclically-induced foundation settlements accurately within an accuracy factor of two (i.e.: predictions fall within 1:2 and 2:1 limits of the measured settlements).

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics

Meeting Name

Fifth Conference

Publisher

Missouri University of Science and Technology

Publication Date

5-24-2010

Document Version

Final Version

Rights

© 2010 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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May 24th, 12:00 AM May 29th, 12:00 AM

Assessment of Liquefaction-Induced Foundation Soil Deformations

San Diego, California

Although there exist some consensus regarding seismic soil liquefaction triggering assessment of free field soil sites, estimating the liquefaction triggering potential beneath building foundations still stays as a controversial and a difficult issue. Assessing liquefaction triggering potential under building foundations requires the estimation of cyclic and static stress state of the soil medium. In the recent studies (e.g. Unutmaz 2008), the cyclic stress ratio corrected for Kα and Kσ effects under and adjacent to building foundations subjected to cyclic loading are to be estimated with the help of a series of 2-D and 3-D numerical simulations for different generic cases. A representative and a maximum cyclic stress ratio terms of the soil-structure-earthquake interaction system, denoted as CSRSSEI,rep and CSRSSEI,max respectively was defined as a function of i) ratio of the pre-earthquake fundamental period of the structure and soil (σ), ii) free field spectral acceleration at the fixed-base period of the structure(SA), iii) the peak ground acceleration of the free field soil sites (PGA), and iv) aspect ratio of the structure (h/B). In this paper, the results of the previously mentioned numerical findings have been verified by using case histories documented after 1999 Kocaeli Earthquake, where significant foundation displacements were observed due to liquefaction of the underlying foundation soils. The foundation soil profiles of these case histories generally consist of silty soils, sand-silt mixtures and silt-clay mixtures. Overburden and procedure corrected SPT-N values vary in the range of 2 to 5 blows/30 cm in the upper 5 meters and gradually increases up to a maximum value of 25 blows/30 cm beyond depths of 5 to 8 m’s. Overlying structures are mainly 3 to 4 storey, residential buildings with no basements. As the concluding remark, the proposed simplified procedures are shown to predict cyclically-induced foundation settlements accurately within an accuracy factor of two (i.e.: predictions fall within 1:2 and 2:1 limits of the measured settlements).