Large Auger Cast Piles

[JedClampett]

I am reviewing a project with 60 foot long 24 inch Auger Cast Piles. I hsve two concerns. One is that the 24 inch size seems larger than the standard 12, 16 or 18 inch. The other concern is that the design requires a 30 ft. long cage to be lowered into the cast pile. Will that work? Won't the grout be setting up at some point between the surface and 30 ft and prevent lowering the cage?

 

[Ron]

JC...I would have your same concerns. 60 feet is a bit deep for augercast. Unless they use some serious retarding admixtures in the grout, putting a cage down 30 feet will be difficult.

If they are fast, they could possibly pull it off. Any consideration to using vibratory insertion of the cage?

 

[woofar]

Hi Jed,

Don't place the cage afterwards, place the cage first and then use a Tremie to place the concrete.

HTH
Michael

 

[jgailla]

If I remember correctly, we had a project with some 75-foot, 18" augercast piles in coastal Georgia. The rebar cage was 25 feet long. They weren't using any admixtures.

There were two contractors on the job. Berkel seemed to be able to do it pretty easily, although there were a couple piles that had to be abandoned. The other contractor had problems, I believe due to the experience of the crew. Many of the cages had to be pushed down with a backhoe. There was much argument, and eventually it was decided that if the cage could be placed by hand to within 5 feet, the last 5 feet could be pushed down with a backhoe.

Ron, you may remember this job, so please correct me if my memory is bad.

 

[InDepth]

Yes, you can use a bentonite or polymer to stabilize the hole, then place the cage, then tremie the concrete. Don't forget the spacers on the rebar cage. 24" x 30 ft deep is fairly typical in California.

 

[Ron]

jgailla...yes, I remember the project and you are correct. Not an easy task but can be done.

 

[JedClampett]

I thought the advantage of Auger Cast Piles was that you installed the grout as the auger was being withdrawn, reducing any caving or necking. If you stabilize the hole with bentonite or polymer or pull the auger and install the cage, aren't you just installing a cast in place drilled shaft?

 

[InDepth]

Take a look at

GEOTECHNICAL ENGINEERING CIRCULAR NO. 8
Design and Construction of Continuous Flight Auger (CFA) Piles

The bentonite and polymer is a suggestion if you don't want to worry about set time of concrete. CFA, cast-in-place shaft, pretty much the same thing with better shaft dimensional control/support. Usually CFA is best for poor soil conditions....but is becoming more popular.

 

[Ron]

JC...that is correct. The use of bentonite or polymer drilling fluid to stabilize the hole is a variation on the concept, but the "Augercast" proprietary system is as you described. In my opinion, the grout method has a lower potential for necking and caving than the drilling fluid method.

 

[lallatin]

I did one project where the augercast piles were typically over 80', with full-depth cages, 18"-24" diameter. The only problems with installing the cages occured when there were delays in stabbing the cage, meaning more than about 5 minutes, AND if there were sand layers at more than about 1/2 depth. Bleed-off of the water stiffens the grout at the permeable layer, and the standing weight of the cage is inadequate to penetrate the slightly drained group. Necking of the soil is never a problem with proper withdrawl rate of the auger, and a full head of grout in the stem. Just look at the pressures involved. A flow-meter is essential. NEVER rely on stroke-counts alone for determining quantities during installation. Out of over 1000 piles in this case, there were fewer than 10 re-insertions needed.

 

[GeoPaveTraffic]

Problems will depend on the quality of the contractor and experience of the crew. 24-inch diameter is at the large end of CFA piles, but they can be done and larger ones are also occationally done. The depth is not a particular problem, CFAs are installed much deeper in some areas.

As for cage insertion, its all about the types of soils and the time it takes to get the cage in the ground. I too have seen the pound it down with the backhoe routine, don't really like it, but likely not to cause a problem either.

 

[DRC1]

Banging 30 ft cages into semi plastic concrete with a backhoe? And nobody has a problem with this?
24 inch pile is a big pile - Why not go with drilled in pier or driven pipe?

 

[JedClampett]

I don't really know why the final choice was made, except that the drilled in piers option required temporary casings.

 

[lallatin]

The big advantage of augercast piles is the speed of installation. The capacity of the concrete pump and the efficiency of spoils removal usually determine the rate of installation. Installation rates for the job I mentioned above varied from 10-15 min/pile, start-to-start if there were no rig-movement issues. No other installation method comes close, especially when up-lift resistance is an issue.

 

[Khaalid]

the length of the pile is 20m, after pulling the casing, we left with cages of different sizes,,,the given design size is 1.35

due to vibration of the hammer while pulling the casing , it ends with different sizes from the cuttoff .
the error is -4 to +2

any suggestions please ?

the client wanted an assurance of future settlement ?

 

[jdonville]

Khaalid,

Start a new post - don't piggyback on an old one.

Jeff

 

[csd72]

Jed,

I have used longer and smaller diameter piles on a recent contiguous pile project with no problems.

 

[jnimens]

Helical piles with 24" diameter shafts would be another solution to consider.... no spoils, less than an hour each to install. Joe Nimens