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RE: Excavating close to a building

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-----Original Message-----
From:	RISSELL, MICHAEL E [Non-Pharmacia/1000]
[mailto:michael.e.rissell(--nospam--at)monsanto.com]
Sent:	Friday, December 21, 2001 9:16 AM
To:	'seaint'
Subject:	Excavating close to a building

My home town in west central Missouri is installing new sewers.  My dad has
a 30 year old pre-engineered metal building, 45'x60', slab on grade with
footings 3' below grade, I think.  The city wants to run a new 22" HDPE
sewer along the 60' side of the building, 6' from the edge of the building,
10' deep.  The building is still in excellent shape and there has never been
any problems with settling, concrete cracking, etc.  Their construction plan
is to use trench boxes at the joints and then backfill in 2' to 3' lifts and
compact to 95% Proctor.  I indicated a big concern with undermining of the
foundation and thought sheet piling was the only sure way to keep the
integrity of the foundation and surrounding soil intact.  Obviously the city
does not want to go to that expense and stands behind the contract with
their contractor that says he is bonded and insured.  Their engineer also
pointed to a similar installation they performed 2 years ago adjacent to a
house, with no problems resulting.  As most of the houses in this area have
basements, I think we have an apples and oranges comparison.  No soils
reports exist for this area and the city also doesn't want that expense.  My
concern also is that even if this gets installed with no problems at the
time, settling could occur 2, 3, or 5 years down the road and it would be
hard/impossible to get any relief at that time, with legal proceedings
almost surely required.  Prevention is much better than a cure anytime!
Anyone have any thoughts on ways to convince them to do this the right way?
Or am I being overly conservative?

You are not being overly conservative.  I suggest that your father hire a
soils engineer and ask him to evaluate their procedure and to suggest a
proper procedure.  It may cost you about $2000, but it would be money well
spent.  Then photograph the building with witnesses to document when the
photo's were taken.  95% compaction is not good enough for the situation you
are describing and you can't get reasonably good compaction with lifts more
than 8" to 12" thick.  Depending on your soils, there are much better and
cheaper methods of protecting your father's building than using piles - your
soils engineer should be able to help you with that.  Chemical stabilization
would be one example if the soils are right for it - You wouldn't have the
impact vibrations potentially causing damage to the building and possibly to
sensitive equipment and it would be cheaper.

Roger C. Davis
Architect
SDS Architects, Inc.



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