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Re: Foundation on Expansive Clay -- Recap

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Flyash has the ability to neutralize the
"expansibility" characteristic of expansive clays,
much in the same way as lime does. Typically, however,
the geotech company needs to do some tests and
recommend an optimum dose of flyash. Flyash/lime
stabilization of expansive soil is common in highway
industry. I have used lime stabilization to neutralize
the expansion potential of high plasticity clay soil
to support concrete slabs. 

Expansive clays will also shrink when starved of
water. I was involved with another project in which
increasing seepage was observed at the downstream side
of a dam. The dam was built to create an artificial
pond. The dam had a drain pipe at the bottom to
facilitate draining the pond in case of emergencies.
Investigation showed that, a few years earlier,  the
bottom of the pond at the head of the drain pipe, was
lined with clay - a good impervious barrier, to stop
the seeapge.  Following some very dry summers, the
clay was deprived of moisture leading to shrinkage
cracks which in turn re-opened the seepage path. Over
a period of some five or six years, the seepage had
increased to an alarming degree. Class "C" Flyash was
mixed in place with the existing clay at the bottom of
the pond. The depth of soil modification was,
approximately, 2 feet.Within a few days the
clay/flyash combination became solid like concrete.
The system is working without any problem for the past
three years.

By the way, you indicated the soil to be silty or
sandy clay. I am curious: What is the LL and PL of the
soil? 

Rajendran
--- Fountain Conner <fconner(--nospam--at)pcola.gulf.net> wrote:
> 
> 'Love it...
> 
> Posting a question to this list is like throwing a
> hand-grenade into a
> confetti factory.
> 
> Recap:
> 
> Foundations for bark blowline in a paper mill. 
> Spacing 70 ft max,
> supporting 18" diameter blowline 20 ft above grade. 
> Soil -- high
> blow-count (n = 20+) silty/sandy clay with
> "potential for expansion".
> 
> My first cut was a drilled pier, setting an oversize
> sleeve in the
> foundation, and plumbing and placing the mast later.
>  The spread footing
> worked out cheaper until I found out about the
> "potential for expansion".
> 
> 'Lots of good suggestions -- I have gone back to a
> single drilled pier for
> each support, setting a 2 foot long piece of 18"
> pipe in the top as a
> sleeve for the 12" diameter mast.  There's no
> potential for uplift, and the
> top of the mast can be a little high, because I'm
> hanging off the side with
> a bracket that we'll set to proper elevation & weld
> in place.  The pipe
> will be hung with a threaded rod and a pipe collar
> which will give a "fine
> adjustment" to the pipe elevation.  Yes, it's
> eccentric, but the load is
> not too large.
> 
> On the comments:
> 
> 1.  To Padmanabhan Rajendran -- What would flyash do
> to relieve the
> expansion?  
> 
> 2.  For David Finley -- There shouldn't be much
> potential for caving.
> 
> 3.  For Eric Green -- 'No trees here.  This is a
> paper mill; they'd make
> paper out of a tree if they had one ;-)
> 
> 4.  For James Lane -- Lime stabilization (related to
> 1, above) might work,
> but I'd prefer to keep it simple.
> 
> 5.  For Bill Polhemus -- You recognized that I went
> "full circle", didn't
> you.  "Blessed are they who run around in circles,
> for they shall be known
> as 'wheels'."  If, however you want to use the
> three-sided wheel, you'll
> have to get clearance from Harold Sprague 
> 
> Again, thanks to all,
> 
> Fountain
> 
> 
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