I really appreciate all the feedback my post has generated. I think it will be
helpful to add some further background.
Under normal circumstances I would not trust a builder, but I have known this
guy for a while and, more importantly, he builds foundations for Rogers
Wireless in Ontario. I felt that his experience with what he does for
commercial installations is somewhat relevant.
His comment was that although we can pour concrete into water, we don't really
know too much about the soil below as the water is there year around and the
soil is very sandy. Thus, the decision to have 2 feet of compacted gravel below
the base. We also chose gravel because of its heaving resistance.
The original foundation specs call for a base of 9 x 9 x 5. Instead, we built
the foundation 11 x 11 x 5, which is close to the specs for the 120' tower, and
using rebar specified for the 120' tower.
Right now there is no tower on the foundation and won't be one until I am
confident we have addressed major concerns. Per my original post, we have
identified the combination of water + freezing as #1 concern, which we
contemplate addressing through drainage, waterproofing, lots of insulation, and
the mound 15' around the base.
Looking back, I realize I should have hired an engineer. But I also believe
that we can build a solid structure now before the tower goes up.
Again, thank you all for the tough but helpful feedback.
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