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[SEAOC] ASCE NO. 58 Use

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     I have encountered this situation when designing a buried structure.  
     I found ASCE 4-86 to be especially useful.  But be careful in it's 
     use.  It considers a yielding and non-yielding wall.  And if you are 
     attempting to save your customer money and there are not other drivers 
     which would dictate thicker walls, your wall will yield.  The equation 
     as shown in ASCE 4-86, I believe is in error.  The equation for the 
     active solution (the Mononobe-Okabe method) has two "angle of wall 
     friction" summed then evaluates the cosine.  This is wrong!  The 
     second term should be the "angle of friction of soil" value.  Use 
     caution because this equation does not consider surcharge effects and 
     you will be in a dilemma there to decide if you will use the 
     equivalent soil height and increase the wall height or some other 
     evaluation.  The other considerable impact is if the wall is loaded 
     under a saturated condition.  You may need to consider the effects of 
     a hydraulic head.  
     
     The most effective means of reducing the amount of concrete in a 
     retaining wall job is to tie the floor diaphragm to the top of the 
     wall and consider a fixed-pinned condition.  This presumes that you 
     have a floor or roof.  You must be sure to carefully detail the 
     connections in this case and check the diaphragm with the structure 
     loads from the building added.  You also need to note on the drawing 
     that the diaphragm shall be in place prior to bakfilling being placed. 
     I understand you dilemma, because my brother is an Architect (with and 
     undergraduate in Civil Engineering, basically enough knowledge to be 
     dangerous) and when I designed the 16' high retaining walls in his 
     personal residence in Salt Lake City he had a fit and the phone call 
     cost me a fortune.
     
     Another area to be cautious when preparing the drawings is the method 
     of backfill placement.  If vibration compactors are used Fang's 
     "Foundation Engineering Handbook, 2nd edition" says this could be the 
     most severe loads the wall will see.  Know how this wall is to be 
     built!
     
     Good luck, and use some of the site inspections money you got for the 
     job to take a walk.  
     
     Scott Horn
     Bechtel Savannah River Site

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