> In Rick's (KC5AJX) post, he mentioned that his holes were too deep. Now,
> I'm not sure you can have too much concrete under a tower, but that's
> another discussion. Anyway, his fix was to shovel loose excavate back
> into the holes.
>
> Now, I know that when you're pouring a footing for a concrete basement
> wall, you must pour onto undisturbed soil. Is the same true for towers?
Yes. I believe the correct procedure is to fill the hole up to the desired
level with gravel or crushed rock, not compacted soil.
I hired a professional contractor to build the base for my U.S. Tower 70'
tubular. The spec on the base was 3'x3'x6' deep. The excavator operator told
us it might be a little larger (rectangular at the top) because his scoop
made it hard to get a perfect square at the top. Ok, that was fine with me.
But he didn't stop digging until he got well over 9 feet deep! I think he
spaced out or something. He might have kept going, but was alerted by a
little water seeping into the hole from the water table. He had to make a
special trip to get gravel to put in the bottom of the hole. He put about
two feet of the stuff down there.
In the end, the hole was indeed rectangular at the top, but actually flared
out towards the bottom of the hole. Sort of a pyramid shape, which is great
for stability. Dimensions at the top are about 3'x4', but down near the
bottom of the hole -- almost 8 feet down -- it's about 4'x5'! It ended up
taking more than twice the concrete we expected -- I think it was close to 6
yards, maybe more. The good news is that I had a fixed price deal with the
contractor and he had to eat the cost of the gravel, extra 'crete and extra
labor. My lucky day -- that base ain't going anywhere. Wish I had a bigger
tower to put on it...
73, Dick, WC1M
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