Seismic coefficient for slope stability
Seismic coefficient for slope stability
(OP)
I would be interested to find some information or discussion about the use of seismic coefficient
in the pseudo static stability analysis of dam and embankment.
Given that a horizontal peak ground acceleration(pga) and a vertical pga are given, based on the
location where the structure is to be built, how do you come up with a seismic coefficient in the
stability analysis. If only one of the two pga’s are known (pgah or pgav), how to estimate the
value of the other ?
Do you only use the pgah, pgav or should you use a combination of the two. What combination is
used ? Some suggestions include pgav = 2/3 pgah. Seismic coefficient in combination,
horizontal = 2/3 pgah, vertical = 1/3 pgav or 4/9 pgah.
Seed 1979, Marcuson 1992 recommended to use seismic coefficient as roughly 1/3 to 2/3 of
pgah.
Looking at the whole spectrum of what people discussed, you can practically pick up any number
and it can be justified ! Any comments ?
Others look at the dam safety guidelines, and usually they find very vague statements.
To throw more confusion, the values provided for the pgah or pgav are even in doubt with
introduction of “Continental Plates theory”, versus “historical data used to determine the pga.
Which is correct ? Which is the recommended practice ?
Regards
in the pseudo static stability analysis of dam and embankment.
Given that a horizontal peak ground acceleration(pga) and a vertical pga are given, based on the
location where the structure is to be built, how do you come up with a seismic coefficient in the
stability analysis. If only one of the two pga’s are known (pgah or pgav), how to estimate the
value of the other ?
Do you only use the pgah, pgav or should you use a combination of the two. What combination is
used ? Some suggestions include pgav = 2/3 pgah. Seismic coefficient in combination,
horizontal = 2/3 pgah, vertical = 1/3 pgav or 4/9 pgah.
Seed 1979, Marcuson 1992 recommended to use seismic coefficient as roughly 1/3 to 2/3 of
pgah.
Looking at the whole spectrum of what people discussed, you can practically pick up any number
and it can be justified ! Any comments ?
Others look at the dam safety guidelines, and usually they find very vague statements.
To throw more confusion, the values provided for the pgah or pgav are even in doubt with
introduction of “Continental Plates theory”, versus “historical data used to determine the pga.
Which is correct ? Which is the recommended practice ?
Regards





RE: Seismic coefficient for slope stability
The ratio between the peak values of horizontal and the vertical components of the ground acceleration at a location is a function of various parameters. The ratio is usually derived by statistical analysis carried out as part of a seismic hazard study.
For example, a figure of 2/3 for vertical/horizontal has been accepted for various USA sites, while Ambraseys (EESD, 1988) gave a figure of 1/2 for various European sites.
Try a literature survey to determine the ratio appropriate to the location of interest to you. If none is available, consult an expert to identify another location, with similar seismological characteristics to the location of interest and for which a widely accepted is available, and use this ratio for your work.
I hope that this note is of some use.
Regards,
Ade
RE: Seismic coefficient for slope stability
Thanks for your input. The selection of the factor to be applied to the seismic coefficient is just the one that I am wondering about. Why in US we use factor 0.67, and in Europe a factor of 0.5 Is the european more conservative? I also recall, that the factor may even vary to as little as 0.33. Whay can't there be a consensus ?
Thanks for your info, anyway.
Regards
RE: Seismic coefficient for slope stability
RE: Seismic coefficient for slope stability
Check out the following publications for the latest opinion from California
1. Guidelines for Evaluating and Mitigating Seismic Hazards in California, CGS Special Publication 117 (previously CDMG)
2. Recommended Procedures for Implementation of DMG Special Publication 117, Guidelines for Analyzing and Mitigating Landslide Hazards in California, ASCE/SCEC publication(available free on the SCEC website)
Hope this helps.