Concerned about backfilled base - Need question answered

[mgmercurio]

I am concerned about something and I wanted to run it by the experts to get
their thoughts.
I have always heard, do not dig out any more dirt than needed for your
pool. Always install the pool on undisturbed earth because there is
a risk of pool failure on any ground that has been backfilled.

So with that in mind, let me explain what has happened. I hired a pool
excavator that said he has 40 years in digging out for and installing
pools. I laid out my pool dig to provide extra room for buttresses and sill plates- allowing 6 more
feet on the sides for the buttresses and 3 feet more on the round ends.
I am burying a 15x30 aquasport 30" in the ground. So my layout that I
marked on the ground with marking paint is 21x33. Also, it is
important to understand that if you are standing at my back door
facing the pool, there is a 12" difference in grade from the right
side to the left. I told the excavator that I want 30" deep from the
RIGHT side (the high side) to level within 1" grade.

I then left to go run some errands. When I came back, the excavator had
dug out 30" deep from the left side (the low side) and was about to
make it level. I stopped him and said he had it backwards...and
that I wanted 30" from the high side. He acknowledged that he made a
mistake and in fact did not know why he did it that way...because you
always dig from the high side down.

Anyway, he backfilled the left side and dug down the right side to
30" and leveled it. Now he also ran his bobcat over the backfilled
side many times even after it rained and the dirt was just moist
from the light rain. Also, the dirt is solid red clay and it is hard
as concrete normally.

So obviously my question to the group is, would you be concerned with the
left side being backfilled? Is there a chance for pool failure? What
would you do to solve this?

Any advice is appreciated.

Thanks!
Matt

 

[Bperry]

Are you putting down sand or gravel at the bottom before the pool goes in? Is the backfilled portion only 12” deep? Digging out an extra 12” of dirt and laying down 12” of stone/sand might be a decent compromise if there is a problem with that little backfill, but I’d let experts comment as I’m not one. You for sure don’t want any organic material in the backfill.

 

[mgmercurio]

Are you putting down sand or gravel at the bottom before the pool goes in? Is the backfilled portion only 12” deep? Digging out an extra 12” of dirt and laying down 12” of stone/sand might be a decent compromise if there is a problem with that little backfill, but I’d let experts comment as I’m not one. You for sure don’t want any organic material in the backfill.

Thanks for the reply. The amount that was "overdug" is about 10 to 15 inches. The dirt that was removed was immediately put back in....then it rained for a day ( a slow steady drizzle all day). The next day he came back in and ran his bob cat over the backfilled area several times (he spent an hour just doing that) .....plus the back fill dirt was the original clay dirt which he pulled out.

As far as sand or rock goes....I am just putting down the standard 3 inches of sand for the bottom of the pool.....oh ...I am also putting down an armor shield pool pad as well....but that won't help with the dirt settling.

 

[Leevon]

From what you have said, there isn't much else that can be done to compact it. A plate compactor won't do any better than the bobcat, and the rain was a help, and the clay soil which is already dense. A larger compactor won't fit in a pool excavation. If anything, you could consider over-excavating 6" which cuts your risk in half or better, and using compacted 3/4 clean base.

 

[Bperry]

Thanks for the reply. The amount that was "overdug" is about 10 to 15 inches. The dirt that was removed was immediately put back in....then it rained for a day ( a slow steady drizzle all day). The next day he came back in and ran his bob cat over the backfilled area several times (he spent an hour just doing that) .....plus the back fill dirt was the original clay dirt which he pulled out.

As far as sand or rock goes....I am just putting down the standard 3 inches of sand for the bottom of the pool.....oh ...I am also putting down an armor shield pool pad as well....but that won't help with the dirt settling.

Probably need a soil engineer to take a look and see but I’ve read that you generally have to compact in layer that aren’t too thick, but don’t know what too thick is under a swimming pool. I found a couple online references if some experts don’t reply. My gut would be that it’s probably fine if he spent an hour compacting ~12” of clay.

Compact Your Fill Properly –

bondedbuilders.com

Soil Considerations in Swimming Pool Construction - Pool Engineering

by Ron Lacher, P.E. Pool Engineering, Inc. What’s important? A. What are the site soil conditions and important characteristics of the soil Is it

www.pooleng.com

 

[sktn77a]

Our pool builder brought in 12 loads of dirt to raise a section of our back yard where the pool went (about 4' max). He compacted it by hammering it with the bucket of his backhoe. That was 25 years ago. We haven't had any problems.

 

[mgmercurio]

Thank you all for the information....It is in progress now and my concern has diminished quite a bit. This is hard clay soil and I am finding that it does not settle much and it compacts very nicely.

Thanks again!