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Re: Geotechnical opinions

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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
-----Original Message-----
From: CLaines <CLaines(--nospam--at)>
To: seaoc(--nospam--at) <seaoc(--nospam--at)>
Date: Friday, May 01, 1998 4:48 PM
Subject: Re: Geotechnical opinions

>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
>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