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RE: Retaining Wall Seismic Loads

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Section 1802.2.7 requires soil report and directs the geotech to provide lateral loads for earthquake motion.  Unless the geotech states that the retaining wall is not going to see additional forces due to earthquake motion, I do not see how you will get around not accounting for seismic forces.  With all the disclaimers geotech put in their report, I do not see the possibility of a California geotech sticking his/her neck out to say retaining walls do not have to be designed for seismic forces.


Gautam, SE


From: Gerard Madden, SE [mailto:gmse4603(--nospam--at)]
Sent: Tuesday, July 21, 2009 3:58 PM
To: seaint(--nospam--at)
Subject: Re: Retaining Wall Seismic Loads


Yes, but by law, the Chapter A provisions of the code cannot be less stringent than the regular building code. In section 1806A.1 in the 2nd paragraph lists the requirements for 12 foot and taller walls.

1806.1 makes no mention of seismic loads in the regular building code.

ERGO, if retaining wall design for seismic loads IS NOT required for 11'-11" walls at schools or hospitals, the building official can't make me design them for a park restroom structure or a trash enclosure.


On Tue, Jul 21, 2009 at 2:38 PM, Gautam Manandhar <Gautam_Manandhar(--nospam--at)> wrote:

I believe the current CBC requires retaining walls to be designed for seismic load regardless of the height (seismic design category D, E, and F).  Section 1802.2.7 states “… The (soil) investigation shall include

      1. A determination of lateral pressure on basement and retaining walls due to earthquake motions …”


Gautam, SE


From: Gerard Madden, SE [mailto:gmse4603(--nospam--at)]
Sent: Tuesday, July 21, 2009 11:53 AM
To: seaint(--nospam--at)

Subject: Re: Retaining Wall Seismic Loads


Along the lines of what others have stated here is my experience:

Soils Engineer will give:

1. A restrained and un-restrained retaining wall active pressures
2. A surcharge for seismic loads (either uniform or inverted triangle, or trapezoidal)
3. The un-restrained wall EFP's would be used with the seismic surcharge even if the wall is restrained
4. ASBP and safety factors are adjusted for the short term loads.

Also, this is not required for walls less than 12 feet tall per DSA.


On Tue, Jul 21, 2009 at 11:40 AM, Salvador Dorado <sdorado(--nospam--at)> wrote:

Chuck Utzman,
       Could you email me the PDF paper directly to
SDORADO(--nospam--at)TBENGINEERINGINC.COM I would like to read it.

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