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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