[TowerTalk] Tower Foundation Pouring

[Roger (K8RI) on TT]

Many times, pouring against undisturbed soil is not possible. an 
alternative to the compactor is a uniform slurry. If done properly it 
will form a solid and uniform connection between the form and the 
undisturbed soil after it sets, or dries.  Keep in mind tat if the base 
or guy anchor is poured in this type of soil, it will need to be larger 
than the normal spec.

I had one guy anchor that was in this type of soil. The NW anchor (abt 4 
X 4 X 6 Deep.)We couldn't pour until the next day. In the morning the 
hole was over 10' wide...just a shallow, circular depression, so it was 
over size, formed, and hand dug with the forms going down with the digging

73,  Roger (K8RI)

On 2/4/2017 1:36 PM, Steve Jones wrote:
> Jim-
>
> Actually, undisturbed soil is not an urban myth, it's just the simplest way
> for the engineer to calculate the foundation design.  The vertical walls of
> the undisturbed soil create friction against the concrete which counts as
> part of the foundation's resistance to the overturning moment.
>
> The key factor in over-excavating is the "high level of compaction".  Soils
> engineers have a way of calculating that level required, designing the depth
> of the engineered lifts, and then measuring the compaction in the field.
> But then if the soil is not suitable (ie. too sandy) it won't adequately
> compact.  In that case you need a mat foundation.  The mat design will be
> much wider and shallower than the typical pier foundation, but with enough
> mass to still resist the overturning moment of the tower.
>
> 73,
> Steve
> N6SJ
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
> JVarney
> Sent: Friday, February 03, 2017 12:11 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Tower Foundation Pouring
>
> There's an urban myth about "undisturbed soil." Hams believe that pouring
> concrete against undisturbed vertical dirt walls is the only way to place a
> footing.  It is often the easiest way to do it and is perfectly acceptable,
> but when soils are soft it can be difficult to do.
>
> The other way to pour a footing, commonly used in commercial construction,
> is to over-excavate, build a full form, like this:
>
> https://goo.gl/MKNbLy
>
> After the concrete cures pull the form. Rent a "jumping jack" or "elephant's
> foot" compactor. Backfill the dirt around the footing in layers, then
> compact it
>
> https://youtu.be/lYndguhIEQc
>
> Done carefully and with a high level of compaction the footing will be as
> good as if the undisturbed soil method was used.
>
> 73 Jim K6OK
>
> Paul W9AC wrote:
>
>>> Despite efforts to brace the walls from blowing out as concreate was
>>> added, we still had slight bowing on the
>>> 140 ft. tower base (a 10 ft. x 10 ft. square).  That resulted in a
>>> less than perfect square on two sides of the top surface.
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-- 

73

Roger (K8RI)


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