That doesn't really qualify as undisturbed soil, and is pretty much what
the manufacturer does not want you to do. Here at my QTH, where I have
rocks and sand with just the right amount of clay, if I take the trouble
I can compact the soil much harder than the original undisturbed soil.
I had a few occasions to do just that as I was building the house. I
lay down a few inches of soil, dampen it just the right amount, and pack
it hard with a compactor or a ram. I let it dry between layers and keep
doing the same thing until I get it where I need it, but I can almost
guarantee your backhoe operator will not take the time to do so, and it
doesn't work well with some soil conditions anyhow. In your case, there
would be just barely more than a foot of clearance around the perimeter
to pack seven feet of backfill, and that is going to be almost
impossible to do well.
I'd tell the backhoe operator to get as close to the 3'6" as possible
(if he is any good at all he should be able to get under 5') and then
I'd just fill the entire hole with concrete. It would probably cost you
an additional three cubic yards worth of concrete.
RICHARD SOLOMON wrote:
> I plan to install an LM-470 in the near future. The base specs are 3'6 X 3'6
> X 7 feet. A note
> on the drawing mentions ..."undisturbed soil"... . The Backhoe Operator tells
> me the hole he
> digs will be more like 6' X 6' and the will use concrete forms to reduce it
> to the required size.
> After the forms are removed, they will backfill the hole.
> What do you folks think of that plan ?
> Thanks, Dick, W1KSZ/7
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