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RE: Seismic Factors for Soil Nail Walls

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On a recent project, the geotech and I discussed his basis for the kh value he was providing. In a nutshell he said after all their research on the methods for determining kh, they concluded that they would always specify ½ of the PGA and feel comfortable with that recommendation.


Incorporating seismic into retaining structures certainly impacts the design of structure, ½ or more of PGA is a substantial force to account for.


Mark D. Baker

Baker Engineering


From: refugio rochin [mailto:refugio311(--nospam--at)]
Sent: Friday, October 17, 2008 9:34 AM
To: seaint(--nospam--at)
Subject: Seismic Factors for Soil Nail Walls


I have a question regarding Soil Nail Walls in a high seismic region.  We are trying to identify the seismic factors for such a wall.  A geotechnical circular No. 7 



as well as the FHWA Soil Nail Manual, utilize the equation Am = (1.45 - A)A where A is the peak ground acceleration at 10% exceedance in 50 years.  This equation however has a maximum at 0.725, and our PGA is 1.25 to 1.1 (located on the San Andreas Fault, site specific spectra and USGS spectra, respectively).  I am not sure if this equation truly applies in this condition.


The target is to define the kh, which is a pseudo-static coefficient input into the Soil Nail programs.



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