Installation of auger cast piles

http://www.eng-tips.com/viewthread.cfm?qid=286278&page=1
abusementpark (Structural)
21 Nov 10 19:21
I'm soon going to be observing the installation of auger cast piles for the first time.

Any tips on things to look for when observing?

Ron (Structural)
21 Nov 10 20:01
Count the pump strokes. Know the volume of each stroke.

Make sure there is sufficient head on the grout to prevent "necking" of the pile.

Compare pumped volume with theoretical pile volume. If different, find out why. If actual < theoretical....necking. If actual > theoretical, low strength stata or lense encountered, or void in soil profile.

Make sure they rebar cage gets to the desired depth and without having to pound it into place.

If tension is consideration, make sure tension bar is pushed straight and to the proper depth.

Check grout strength and flow.

I'm sure I've probably forgotten something, but off the "top of my head" these are critical.

msquared48 (Structural)
22 Nov 10 2:25
Some very basic additional thoughts to add here...

Check the placement of the pile before it is poured to make sure it is according to plan.

Make sure the cage steel is of the right size and grade.


dirtydude (Geotechnical)
22 Nov 10 14:07
To add to what Ron listed, it is OK and actually preferrable to have the pumped volume to be greater than the theoretical. This is due to the 'head' alluded to and the fact that the auger is rarely absolutely straight. So, while the auger 'wobbles' to the desired tip, a hole of slightly greater diameter will be drilled than theoretical.

Centralizing devices are a great addition, if not required by spec, to ensure proper reinforcing steel installation.

Ron (Structural)
23 Nov 10 17:23
ABP...the Deep Foundations Institute has an augercast pile inspection handbook. It's small and cheap, if still available. I looked on my bookshelf and found one...should have done that before I responded!! If it's not available anymore, let me know and I'll copy it and post it.

Ron

abusementpark (Structural)
23 Nov 10 21:18

Quote:
Count the pump strokes. Know the volume of each stroke.


How do you know the volume of each stroke?

Quote:
Make sure there is sufficient head on the grout to prevent "necking" of the pile.

Compare pumped volume with theoretical pile volume. If different, find out why. If actual < theoretical....necking. If actual > theoretical, low strength stata or lense encountered, or void in soil profile.

I was told that typical overages in my region are 15%-30%.

How do you assure sufficient head?

I should clarify that I am observing, not inspecting.

Ron (Structural)
24 Nov 10 6:38
ABP...simple grout pumps are positive displacement pumps. They have a piston that displaces a volume (bore area x stroke) for each stroke. Some contractors use variable displacement pumps...which should have a device to display the volume or flow.

If you know the volume of the grout being pumped at all times and you know the extraction rate of the auger, you can estimate the head on the grout.

As DD noted, the overage will be typical. Be more concerned about undervolume conditions. Over just means you're pumping a little more grout. Under can mean a structural deficiency.

dirtydude (Geotechnical)
24 Nov 10 13:34
Contractors usually calibrate the pumps prior to the intallation of any piles. The grout is pumped into a 55 gallon drum. The drum should measured, 55 gallon drums are not usually 55 gallons. The drum is filled with grout while counting the strokes. Once filled, the volume per stroke can be determined and the appropriate number of strokes required to create a postive head as well as strokes pumped per increment of pile.