90 ft. Auger Cast Piling 2

[REIIC]

We have a project in south Louisiana proposing to use 18-inch diam x 90 ft. auger cast piles. I assume the cage will have to be placed after the auger is removed with poor soil conditions we have here. Does this sound possible?

 

[DLite30]

That's probably your best option.

The other option is to use casing, which requires more labor and more machinery.

 

[REIIC]

So the cage will have to be pushed into place with hopes its straigh and true before the concrete gets to stiff? I see some problems.

 

[JedClampett]

I asked the same question, but with 60 ft. long piers.
thread256-239787
Not much help there, but there was a great Federal Highway document that I found on Auger Cast. I'll look for the link.

 

[JedClampett]

Here's the link:

http://www.fhwa.dot.gov/engineering/geotech/pubs/gec8/gec8.pdf

 

[dirtydude]

Augercast piles do not use casings, they have the 'hole' held open by the grout that is pumped in. Since the grout uses sand as it's only aggregate, it allows for the cages to be placed.

If your piles are 90 feet deep, then the minimum cage length should be at least 30 feet (1/3 total length) depending on the seismic site class. Proper use of centralizing devices and an appropriately design grout mix will allow for reinforcing cage ease of placement.

As a side note, some projects in Florida require full length cages, and their piles can exceed 100 feet. The high water table prevents the grout from curing very quickly.

 

[REIIC]

Think that's got it guys. Thanks.

 

[Zambo]

dirtydude,

that post all made sense up to "the high water table prevents the grout from curing very quickly". I doubt that's the case.

 

[Ron]

Zambo..you're right.

 

[hokie66]

Might not prevent it from curing normally, but might prevent it from curing at all if sections of the pile are infiltrated. I feel uncomfortable with depending on grouting below the water table, particularly that far down.

 

[REIIC]

hokie, Well now I'm back to uncomfortable. We definately have a high ground water table. Drainage ditches all have standing water year round.

Install a couple of auger cast piles and load test them. Do they need to cure 28 days?

There will be 60 ft. timber piles within 7 ft. of the auger cast piles. Should these be installed first? Will the driving vibration disturb curing of the grout?

 

[Ron]

REIIC...no real need for concern. A key to successful Augercast installation is monitoring the critical aspects of the application. The auger extraction rate and grout pressures are critical.

Reinforcing cages can be pushed into the top of the pile and centered. If subjected to uplift, a single bar in addition to the cage can be extended deeper into the pile.

Your application is not uncommon. Vet the contractors for experience and check successful applications. Provide full time monitoring of the application, preferably by an engineer.

 

[dirtydude]

If the soil for which the pile is installed is 'dry', it will wick away whatever moisture is within the grout causing it to become less plastic. That is the statement I was trying to make.

Pile load tests on augercast piles can be tested within 7 days if the grout mix is adjust appropriately. Keep in mind the point of a pile load test is the verify geotechnical assumptions made during the design. The structural integrity of the pile should not need to be tested if the pile is installed properly.

 

[Zambo]

dirtydude,

it is correct that rather than the high water table causing the curing issue there is a consoderation that if you are casting against dry soil you can lose moisture from the grout.

If possible I would wait 28 days for the pile test. There is some drying shrinkage as cementitious materials hydrate and leaving a longer period before testing will ensure that any space has been closed.

As Ron states the work procedures are key to ensuring that the grout pressure keeps the water out of your excavation and avoids infiltration of water into the pile. Grout quality and density are also importance.

 

[Geostructsparks]

Just to point out that there is not much of a cage, only the diameter that can fit through the center of the augers. As noted above, often this consists of a single bar at greater depth. I would generally not trust these things for any significant lateral pile capacity (since I am in a high seismic area.

 

[GeoPaveTraffic]

Geostructsparks,

In all of the ACP piles that I have done, the cage is installed after the auger is removed from the hole. In that way the cage can be of any resonable size. The length of cage shold be no longer than is needed based on a lateral analysis of the pile and uplift capacity (if needed) should be provided by a single bar to the bottom of the pile.

 

[dirtydude]

Zambo - While waiting 28 days may be the prudent thing to do, think of the cost implications of having the construction equipment, and possibly the crew, on standby. These costs would outweigh any benefit of the additional cure on the pile, in my mind.

 

[REIIC]

Any concerns over driving timber pile ajacent to ACP or should all timber piles go in first. Cure time will take care of itself if timber piles are installed after ACPs. There are 300 +/- timber piles.

 

[JedClampett]

I'd put in the timber piles first. The auger cast installation should only disturb a very local area, while the pile driving can vibrate the whole site.

 

[dirtydude]

Putting the timber piles in first is one solution, although it makes the site somewhat difficult to navigate for the augercast pile installation.

The other solution would be to drive the timber piles second, and ensure that the initial set has taken for all of the augercast piles.

Either way, vibrations are a concern for the augercast piles.