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Re: 20' foundation walls

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Valerie,

The words "20' deep" and "Aggressive time table" suggest a multi residential development by a developer who is putting a lot of emphasis on cost savings and less on some other important aspects of the project.

I think you need a geotechnical report; that would answer many of your questions. I think no responsible contractor would undertake a significant project requiring 20' excavation without one. I also think an experienced, well financed, developer shouldn't either. If you're still in design stage and haven't started the BP application you have time to get one without causing delay.

Regarding the other questions you raise, "Ways and means" are generally the responsibility of the contractor; he will probably have 8' forms, therefore, he will probably want to do it in three lifts. Unless you have a strong objection to multiple lifts that's probably the way it will go. You probably have to provide a detail for rebar splices at cold pour joints.

Regarding concrete mix design, there are probably local ready mix suppliers who have who have good technical support who will be ready and willing to help you. In Alberta, Canada, where I practice, many of the geotechnical companies also provide concrete testing and mix design expertise. One consideration where I practice is whether or not to use sulphate resistant Portland cement in the concrete mix design; this varies significantly from site to site and it has a significant cost implication. The answer to this will come from the geotechnical report. You will need concrete quality control testing for the project so it might be worth your while to select a consultant who provides both services.

       I hope this has been helpful and not just muddied the waters.

Regards,

H. Daryl Richardson

----- Original Message ----- From: "Valerie Eskelsen" <v.t.eskelsen(--nospam--at)sbcglobal.net>
To: <seaint-seaosc(--nospam--at)mail-list.com>
Sent: Saturday, October 20, 2012 11:46 PM
Subject: [SEAINT-SEAOSC] 20' foundation walls

Dear List,

Designing 20' deep, restrained foundation walls for a residential
structure. The water table will not be known until the dig is begun.
Aggressive timetable of course.

I am expecting some water regardless, and am concerned that 20' is too deep
for a single pour.
There is rebar, of course, but is there more about the concrete mix or the lift heights that I should be concerned about and specifying to the
contractor?

Thank you for any direction that you might be able to give.
-----------------------------
Valerie Eskelsen, P.E.

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