Location

San Diego, California

Session Start Date

5-24-2010

Session End Date

5-29-2010

Abstract

The purpose of this study is to identify and analyze the differences between the various methods of slope stability analysis with respect to the height of the water table, and earthquake excitation. This was achieved through analysis of a cross section of the 2005 Bluebird Canyon Landslide in Laguna Beach, California. The profile was analyzed with the slope stability analysis software Rocscience Slide, using eight different methods, varying the water table in two meter increments and the seismic coefficient in increments of one tenth. A total of 15 different water tables were used with 10 different seismic loadings, yielding a relatively large set of data. Additionally, spreadsheets were constructed for analysis using Bishop’s Simplified Method with the pseudo static approach for seismic loading. While all of the methods yielded results for the tests with no seismic excitation, the number of methods yielding results diminished as the seismic coefficient increased. The only two methods that gave results for all loading conditions were the Army Corp #2 method and the Ordinary Method of Slice. In general, the Army Corp #2 method gave the least conservative results, while the Ordinary Method of Slice gave the most conservative results. This was true for almost all loading conditions and water tables. Another trend was Bishop’s Simplified Method giving nearly identical results to the Jambu Corrected method, and the spreadsheet results being nearly the same as the Jambu Simplified method. As expected, lowering the water table increased the safety factor for nearly all the methods. This beneficial effect was found to diminish as the water table lowered, and as the seismic coefficient increased. The incremental effect of lowering the water table on the safety factor was found to be nearly the same for all cases except the Army Corp #2 method. In this case, lower safety factors were obtained for lowering the water table in the presence of seismic excitation. As the seismic coefficient increased, the beneficial effect of lowering the water table decreased. The effect that the seismic coefficient had on safety factor also decreased with an increase in the coefficient. Furthermore, it was found that for lower water tables, the effect that the seismic coefficient has on safety factor is relatively large, while the effect is small for full or nearly full water tables. This was found to be true for all cases except the Army Corp #2 method.

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

Seismic Slope Stability of Reactivated Landslides — A Performance Based Analysis

San Diego, California

The purpose of this study is to identify and analyze the differences between the various methods of slope stability analysis with respect to the height of the water table, and earthquake excitation. This was achieved through analysis of a cross section of the 2005 Bluebird Canyon Landslide in Laguna Beach, California. The profile was analyzed with the slope stability analysis software Rocscience Slide, using eight different methods, varying the water table in two meter increments and the seismic coefficient in increments of one tenth. A total of 15 different water tables were used with 10 different seismic loadings, yielding a relatively large set of data. Additionally, spreadsheets were constructed for analysis using Bishop’s Simplified Method with the pseudo static approach for seismic loading. While all of the methods yielded results for the tests with no seismic excitation, the number of methods yielding results diminished as the seismic coefficient increased. The only two methods that gave results for all loading conditions were the Army Corp #2 method and the Ordinary Method of Slice. In general, the Army Corp #2 method gave the least conservative results, while the Ordinary Method of Slice gave the most conservative results. This was true for almost all loading conditions and water tables. Another trend was Bishop’s Simplified Method giving nearly identical results to the Jambu Corrected method, and the spreadsheet results being nearly the same as the Jambu Simplified method. As expected, lowering the water table increased the safety factor for nearly all the methods. This beneficial effect was found to diminish as the water table lowered, and as the seismic coefficient increased. The incremental effect of lowering the water table on the safety factor was found to be nearly the same for all cases except the Army Corp #2 method. In this case, lower safety factors were obtained for lowering the water table in the presence of seismic excitation. As the seismic coefficient increased, the beneficial effect of lowering the water table decreased. The effect that the seismic coefficient had on safety factor also decreased with an increase in the coefficient. Furthermore, it was found that for lower water tables, the effect that the seismic coefficient has on safety factor is relatively large, while the effect is small for full or nearly full water tables. This was found to be true for all cases except the Army Corp #2 method.