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Re: Geotechnical opinions

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Dear Charles,

I had a 140 year old church built from stone on a river flat.  Two stories
of masonry scissor truss roof.

I was built over unconsolidated sand lens.  It settled differtially after
earthquake.  

A 1960,s building of great masonry and concrete floors rotated.  We could
measure the rotation two ways by survey and cause it pulled a walkway out of
an adjacent building.  thing to remeber if connecting two buildings in
earthquake.

DJ Douglas (good geotech engineers) drilled site replied and said settlement
of loose sands.

I had no reason to doubt them.  This was an absoultely flat site.

Also saw it about a mile away in a warehouse owned by the local council.

It does happen.  It was studied at univerity in Bangkok and testing there
showed it as well.  Canna remember the author.

good luck.

John Nichols




At 16:41 1/05/98 -0400, you wrote:
>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
>
>
>
>