Retaining wall design in California

[koodi]

The California Building Code (the UBC97 code with the state's additional guidelines) states, retaining walls over 12 ft must be designed for earthquakes--a quake with a 500 yr recurrence interval.

The peak acceleration for the quake is 0.65 gravities. Using this acceleration in the Monobe Okabe equation results in RW's with a stability F.S. >8 under normal service conditions.

IS THERE AN ALTERNATIVE EQATION THAT IS MORE CONSERVATIVE THAN THE MONOBE EQ? SHOULD THE PEAK ACCELERATION BE USED IN THE EQUATION? IS THERE ANY GUIDANCE FOR WHAT "EARTHQUAKE DESIGN FOR RETAINING WALLS" ENTAILS?

P.S. The CBC offers virtually no guidance. The walls will result in NO collateral damage if they fail. The height of the wall varies and it will have a maximum height of 30 ft. The soil is typical sandy gravel. Ground water is not an issue.

 

[bridgeboy]

Are you sure this wall is 30 ft tall? If so, this is a serious retaining wall.

 

[koodi]

No bridgeboy, the wall is 25 feet high--my mistake. Yes this is a serious retaining wall. Unfortunatley I think I've posted the question in the wrong forum.

I am reposting it in the "earth retention engineering forum." With the correct height of 25 feet.

 

[RWF7437]

The AASHTO Design Standards may help you a little here. If you don't have them see if you can find a copy at CalTrans. My recollection is that the Monobe-Okabe pseudo static method is not considered valid for peak ground accelerations greater than 0.40 g. For you case you may need to consult a geotechnical engineering capable of doing a dynamic analysis of this wall.