Should I compact fresh infill soil when backfilling in-ground pool? 2

[HoneywellOS2000]

I am going to remove my in-ground gunite swimming pool. The three contractors that I have spoken to have stated that their method of compacting backfilled soil consists of either running a 30K-lbs trackhoe or a smaller Bobcat-type loader back and forth across each 10 cubic yards of soil dumped into the excavated hole. The contractors stated that typically each one-foot lift of soil will be compacted in this manner.

The native soil in my North Texas region where I live is a very heavy expansive black clay.

It would seem that the large footprint of the track on the trackhoe would NOT equate to enough compaction force to properly prepare the soil against settling. The deep end of the pool is 9 feet deep.

Am I wrong in my thinking?

Should I rent a walk-behind drum pad foot roller (sheepsfoot style) and compact the soil to a denser degree between soil lifts?

Thank you for your interest in assisting me.

 

[Ron]

Rent the compactor. They cannot maneuver their equipment adequately in such a small space to get full coverage.

Compaction will not control your overall settlement; however, it needs to be done to achieve a modicum of uniformity in the surface soils for better bearing.

 

[HoneywellOS2000]

Thank you, Ron, for your quick reply.

I had my doubts that the contractors' method of compaction would be adequate for the task. I will rent a compactor.

 

[PEinc]

It's amazing that residential contractors never compact backfill soils. It's more amazing that no one ever makes them do it.

http://www.PeirceEngineering.com

 

[HoneywellOS2000]

PEinc,

The excavation contractors that I have talked to about my project have extremely poor knowledge (and education) differentiating between soil settlement and soil load bearing capacity. They seem to think that having received zero complaints in the past decade equates that their compaction methods are sound.

Maybe. Maybe not. A lot would depend if the psi load on the final soil grade was St. Augustine grass, an asphalt driveway, or a house foundation extension.

The contractors I am dealing with are also poorly equipped equipment-wise in their ability to properly compact backfill soils even if they wanted to and had the proper training.

When I have approached a contractor about using a rented compactor, it's the old "It'll slow me down" blues.

I'm still on the hunt for another contractor to interview.

Thanks for the reply, PEinc.

 

[PEinc]

Almost all residential contractors will sing the same tune about compaction. They probably did not price the job to properly compact the backfill. If you want it compacted, the contractor will resist or want more money. You and I will never solve this problem. If you think you will ever need to build above the old swimming pool, insist on compaction.
If you rent a compactor, who will run it? If you run it, you will be blamed for slowing down the contractor and will be responsible for obtaining proper compaction. If the contractor runs the compactor, he should rent it and be responsible for the finished product.

Good luck.

http://www.PeirceEngineering.com

 

[HoneywellOS2000]

**Update** **Update**

I have spoken to a much larger contractor that has the know-how and equipment to compact backfill soils.

This contractor has proposed backfilling with SELECT FILL soil in 1 foot lifts followed by roller compacting with a sheepsfoot drum attachment on a Bobcat excavator. Due to the added expense (and overkill) for a residential backyard, both myself and the contractor have decided that there will be no soil compaction tests between lifts.

Since I have adequate backyard space around the pool, the backfill material can be stored onsite so a Bobcat operator can place the backfill when he wants its and where he needs it, and not be impinged upon by dump trucks attempting to dump 10-20 yards of soil at once into the excavation.

The extra labor and compaction costs will add approximately $2-3K to the project. The contractor will give me a formal bid with several levels of cost saving measures by tomorrow (Friday, April 16).

Does anyone have any thoughts -- pro or con -- on using SELECT FILL soil as backfill instead of the native black expansive clay? All indications from my contractor, as well as my own research, have determined that this type of backfill would be far superior to the native soil.

.

 

[PEinc]

Will you be breaking up the bottom of the pool so that any water that seeps into the select fill will (slowly) drain out? I don't have any experience with expansive soils so I'm not sure whether or not breaking up the slab is a good idea or not. Also, sheeps-foot rollers are usually used for compacting clays. Your select fill should be granular soil. Therefore, you may want to uses a walk-behind vibratory roller or plate tamper. Your pool is probably not too big (i.e., unlike a large public pool). Therefore, dragging around a sheeps-foot roller by a Bobcat inside a pooy may be cumbersome and hard to use in any corners. I'd let the Bobcat feed and spread the fill while someone uses a walk-behind roller or plate tamper.

http://www.PeirceEngineering.com

 

[HoneywellOS2000]

PEinc,

I plan on completely removing the concrete shell. There will be no remnants of the pool left in the ground.

I did question this contractor about using a sheepsfoot roller on this type of select fill soil, and I had the impression that his method was about speed and ease of doing the compaction.

I will discuss this very topic of effectively compacting this soil (especially the corners and edges abutting the rounded, curved sidewall of the excavation) using a smooth roller/plate compactor instead.

Thanks for your insight, PEinc.

 

[PEinc]

If the expansive clay extends up to the ground surface outside of the pool area, you may want to cap the select backfill with a lift of the same clay to prevent water from filling up the select materialm and then feeding moisture to the lower, virgn clay.

http://www.PeirceEngineering.com