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Re: Geotechnical opinions

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This settlement  can occur even for very well compacted soils.  In the
1971 San Fernando Earthquake, highway bridge approach fills - typically
25 or more feet of 90-95% (AASHTO) compacted select materials - settled
up to two feet.   

Russ Nester
rnester(--nospam--at)juno.com
_______________________________________________________________
>It seems to me that if you have uncompacted soil and apply pressure to 
>it
>(as a building foundation does), then it will compress a certain 
>amount.
>Then if you maintain that pressure and vibrate the assembly (as an
>earthquake does), the soil will compact further.
>
>Lew Midlam, PE
>NOT a soils engineer
>http://www.lcm.com
>===================
>
>
>>Need some geotechnical input.
>>
>>My Van Nuys client has a soils report that includes the analysis of 4 
>test
>>holes. The analysis found that 12-inches of fill and upper 2-feet of 
>native
>>soil that support the raised floor foundation are unconsolidated 
>(less than
>>90% compaction). The fill and native soils are silty sand, sandy 
>silt, and
>>silty clays. The report concludes that this "somewhat loose and 
>porous"
>>material resulted from the 1994 Northridge quake, and this loose soil 
>is
>the
>>cause of the settlement of this 1950?s house. The site is basically 
>flat.
>>
>>I thought liquifacation was the only mechanism that could cause 
>foundation
>>settlement in an earthquake, assuming a flat site and no slope 
>failures. A
>>basically granular soil would become more compact in a quake, not 
>looser.
>>
>>My opinion is that the soils have always been loose, and combined 
>with poor
>>site drainage, nearby trees, and age, the house has settled as the
>>unconsolidated material has collapsed.
>>
>>Am I off base?
>>
>>Charles Laines, S.E.
>>Long Beach, California

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