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Overturning due to settlement

Overturning due to settlement

Overturning due to settlement

(OP)
I'm looking for discussion on overturning for a mat footing.  The site in question is south of Houston and has deep (30' investigated) saturated (H2O @ 3') clays with low strength.  Torvane range 0.5 to 1.5 tsf.,  penetrometer range 0.75 to 2.5, UU's 0.6 to 1.8 tsf.  The foundation is for a 50' to 75' tall (unknown at present), narrow vertical vessel.  The footing will be lightly loaded, but I am concerned about overturning due to eccentricity.  Any eccentricity could lead to differential settlements which would increase the eccentricity (and on and on) and I end up with the "leaning vessel of Houston".  However, I don't want to specify deep foundations if it is not warranted.  Should mat foundations be considered for this case?  

RE: Overturning due to settlement

The clays are not that soft.  What do you have as far as consolidation data?  This reminds me of Sarnia clays - but I'll need more data to confirm.  To my knowledge we never had problems with our projects there (many oil refineries).  Can you give some more data - consolidation, Atterberg's, expansive details, etc. of the clays? Thanks.

RE: Overturning due to settlement

(OP)
Just a little more info. clay: top 3'- LL=52, PL=18, PI=34.  Below 3' - LL=34, PL=17, PI=17. Consolidation testing was beyond the scope, however, the secant modulus for 1/2 peak stress from the UU tests averages about 100 ksf.  Also, the vessle may only be 40' tall, 8' diameter, 140 kips (fully loaded).

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