Soil Compaction – “Trash Pit”

[Marc]

Long story short…. A few weeks ago we discovered that our pool was built on top of a trash pit filled with roots and trees from lot-clearing 20 years ago. We contracted a poolbuilder in Atlanta, to excevate the pit, backfill and rebuilt the pool/deck. The used “jumping jacks” to compact the soil every 2-3 feet, with a maximum backfill depth of 10 feet. The first hard rain resulted in up to 6 inch settling. The builder wants to fill in some more dirt and start pooring the deck.

I don’t feel comfortable after the recent settling and deployed compacting technique (jumping jacks), and I am looking for a long term solution to avoid future settling or cracking. The “fix” as suggested by the builder is no longer acceptable.

What can I do? Start from scratch, or can up to 10ft. be compacked? Thanks a lot for any suggestions.

[dp]

have some soil enegeneering company come and look at whats what

this will set you on the right track so your not makeing a money pit from a trash pit

[pb]

I don’t know what to do now, but I can sure see why you have the problem. When I was a construction inspector for the highway department we used those jumping jacks to compact backfill in trenches, and the limit was 3 inch lifts, not 2-3 feet. Even the heaviest equipment compacting road base only did 6″ lifts, and nothing in our inventory could compact ten feet.

What happens in a case like yours is that the soil compacts from the top, and when the top few inches gets compacted it starts functioning as a unit, sort of a shell that spreads and absorbs subsequent impacts, leaving the backfill soil beneath it undisturbed.

[Ron T.]

Unfortunately, the only proper fix requires removing at least 9ft of the fill and compacting each 1ft lift (1ft of additional backfill) will a large vibratory roller compactor. If you cannot find a contractor with such a unit, then a smaller compactor will do the trick, but you need to compact even smaller lifts (about 6 inches). As a construction inspector for over 5 years, and currently a field engineer for a construction company now for over 7 years that is my professional opinion. Depending on the type of soil you are using as backfill, and it’s degree of moisture content as it is being backfilled, the amount of compaction required changes. Scientifically, a soil has a desired range of moisture content in which maximum compaction can occur. The closer you are to that range, the easier it is to achieve adequate compaction. A soils engineer will sample the soil, determine it’s optimum moisture content, determine it’s maximum density, and inform you what proper measures should be undertaken to compact the soil as it is backfilled. A good soils engineer will not only observe your backfilling activities, but also test the compaction of the soil to insure it makes 95% (at least) of the maximum density in it’s compacted state). Sorry to be the bearer of bad news, but as another replier said “there is NO compaction method that will successfully compact a 10ft lift!”

[Author]

Posts