Auger Pile Reinforcement & Installation 1

[dianium500]

I have 35 ft auger piles for a residential home I did the engineering for and the subcontractor is stating that they cannot run the #3 ties greater than 15 ft down the length of the 35ft required. Further more, they are saying that they bundle the bars together after 15 ft and only use half the number of bars. They state that if they don't bundle the bars together, they struggle to get them into the pile. I don't want to accuse someone of cutting corners, but it seems to me that they are. I have attached their detail so you can see what I am referring too.

Piles are 14" in diameter, and were used on this project because of a muck layer that was encountered on the property, so I am mostly relying on compression. 35 ft was the recommendation from the soils engineer on the pile length to develop the capacity needed.

Does anyone have any experience with this? Thanks in advanced.

 

[GeoPaveTraffic]

A good contractor with proper installation technics should be able to install the full cage to the full depth.

I've seen many cages installed that were larger to similar depths.

The real question, in my mind, is why do you need a cage to such a great depth? You don't need a cage for compressive load, only lateral and/or uplift.

Mike Lambert

 

[dcarr82775]

I see augercast with a single larger bar down the middle that is full length and then a partial depth full cage as you describe. Seems like your contractor is proposing something in that vein.

I have done some 55-ft piers (30" diameter) CFA piers (just think heavy duty auger cast) with respectable full length cages. It requires a mix with a lot of admixtures to get a high slump and some other chemicals to lower viscosity. Also needed the help of equipment to push the cage in the final 10-ft or so.

 

[oldestguy]

How can anyone answer usefully when missing are: Soil data and code requirements as for earthquake protection, loads etc.

 

[TLHS]

Style of construction for augured piles seems to vary greatly in different areas of north america when we've had these discussion in the past. In western Canada I've seen a lot of full length cages to reasonable depths.

I've also done piles to this length with full cages before. While you don't necessarily need it for compression and your moment generally drops fairly low after the uppermost layer of soil, you'd still want it if you have seismic concerns or if you have non-competent material near the top and lateral forces.

 

[Ron]

Agree with dcarr....single large rebar down the middle to develop uplift, then lighter cage for other loads.

I will assume you are in an area similar to the one in which I practice (Florida, USA). I surmise that because of the pile type and depth as recommended by the geotech.

If you are relying mostly on compression, as noted by GPT there is not much need for a rebar cage. That is mostly for loads other than compression.

Don't let the contractor rule the design. Tell him what you need and demand it. Just because it isn't the easiest approach for him is not your problem. He can place a cage to full depth if necessary by proper timing and concrete mix control.

 

[dianium500]

Thank you guys for your help! Ron, is correct, in Florida the Geotech recommends a depth and pile diameter, so I base my design on the loads provided. I just really needed your opinion. Thanks again!

 

[BUGGAR]

Always wise to check out your Geotech. Alternatively you can have him discuss his recommendations with the contractor, preferably prior to bid.