Location

San Diego, California

Session Start Date

5-24-2010

Session End Date

5-29-2010

Abstract

This paper is an attempt to clarify a possible confusion regarding which maximum ground acceleration (amax) should be used when performing a site-specific liquefaction analysis. Usually, one-dimensional free-field site response analysis is performed to estimate amax at the foundation elevation and the strain-compatible soil parameters within the soil profile. From the soil-structure interaction (SSI) analysis perspective, this calculation is repeated for the best-estimate, lower-bound, and upper-bound soil profiles. For this, the shear moduli are adjusted using a coefficient of variation (cv) to account for the spatial variation in the soil properties and the uncertainties in SSI calculations. The procedure is explained in ASCE 4-98. On the other hand, establishing a design amax is open to interpretation in current guidelines and procedures that discuss the liquefaction analysis. The simplified cyclic stress ratio (CSR) procedure is an empirical method that uses a depth dependent stress reduction factor (rd). In the CSR procedure, amax corresponds to the magnitude of an earthquake that is assumed to occur at the site. The question is, should the amax from the one-dimensional response analysis using the best estimate (or representative) soil profile be used in liquefaction analysis? Or, should the average or possibly the least favorable amax be used? If the least favorable amax is used, then the corresponding soil profile should also be used in liquefaction analyses. Historically, rd values are based on studies done using different earthquake time histories and average soil profiles. In this study, a small scale parametric study is conducted to show that the average amax from the one-dimensional response analyses with best estimate soil profile is appropriate to use in simplified liquefaction analyses.

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

Selection of an Appropriate amax for Liquefaction Analyses from One-Dimensional Site Response Analyses

San Diego, California

This paper is an attempt to clarify a possible confusion regarding which maximum ground acceleration (amax) should be used when performing a site-specific liquefaction analysis. Usually, one-dimensional free-field site response analysis is performed to estimate amax at the foundation elevation and the strain-compatible soil parameters within the soil profile. From the soil-structure interaction (SSI) analysis perspective, this calculation is repeated for the best-estimate, lower-bound, and upper-bound soil profiles. For this, the shear moduli are adjusted using a coefficient of variation (cv) to account for the spatial variation in the soil properties and the uncertainties in SSI calculations. The procedure is explained in ASCE 4-98. On the other hand, establishing a design amax is open to interpretation in current guidelines and procedures that discuss the liquefaction analysis. The simplified cyclic stress ratio (CSR) procedure is an empirical method that uses a depth dependent stress reduction factor (rd). In the CSR procedure, amax corresponds to the magnitude of an earthquake that is assumed to occur at the site. The question is, should the amax from the one-dimensional response analysis using the best estimate (or representative) soil profile be used in liquefaction analysis? Or, should the average or possibly the least favorable amax be used? If the least favorable amax is used, then the corresponding soil profile should also be used in liquefaction analyses. Historically, rd values are based on studies done using different earthquake time histories and average soil profiles. In this study, a small scale parametric study is conducted to show that the average amax from the one-dimensional response analyses with best estimate soil profile is appropriate to use in simplified liquefaction analyses.