Augercast pile grout factor 2

[qualitypro]

We installed six Augercast piles (16" dia x 50ft depth) for a generator step up transformer. For one of the six piles when reviewing the Auger cast pile log report we see that the grout factor for 5-10 ft is 0.88, 10-15 ft is 0.35 and 15-20 ft is 0.88 while the for rest of the depth upto 50 ft the grout factor is in the range of 1.2-1.8. The other piles are acceptable as they have grout factors > 1 primarily. The pile report also states that this subject pile has a overall grout factor of 1.39. While manual counting of the pump strokes were done we understand that during times when the pump is running inconsistently, there are chances that the inspector could have counted “missed pump strokes” thus indicating more volume than actually pumped. The pedestal on these piles have already been poured. How can we ensure that if there is necking in this pile and if it should be a serious concern? Is there a criteria for what the minimum grout factor should be although the overall grout factor is 1.39?

 

[ron9876]

The grout factors indicate that there was necking of the pile. If there was a full reinforcing cage for at least the top portion of the pile it likely was hard to install and the inspector/contractor should have noticed it. I would check with the geotechnical enginner to see if they have a method to check the pile in place. You may need to abandon the pile and add a replacement pile.

 

[GeoPaveTraffic]

I agree with ron9876, if there was a full length cage, you are good; otherwise you need to add a pile.

This shows why all foundations should be observed by a qualified geotechnical engineer or their representative during construction. If someone was watching the piles go in, then this should have been identified right then. At that time it would have been a very easy fix. Now it is going to be a very expensive fix.

Mike Lambert

 

[hokie66]

GeoPaveTraffic,
What is the logic of accepting the pile if there is a full length cage? The logs still show that the pile has necked.

 

[dik]

Hokie's on the mark... I would have expected a grout factor closer to, or greater than 1.0

Dik

 

[GeoPaveTraffic]

Short answer, based on the couple thousand ACIP I've watched installed, if the pile has a significant neck, then you will not be able to get a full length cage in the pile.

Longer answer, if the overall grout factor is less than 1.0, then I agree the pile should imeadiately be rejected, redrilled, and regrouted; simple fix. If the grout factor for a short zone is less than 1, but the factor below and above that area is significantly greater than 1, the pile may be fine and installation of a full length cage with out problem is a good indicator of a fine pile.

hokie66 - If enough grout head is built up below the area of the pile where the auger is pulled too quickly, then that grout head will provide grout to the low grout zone and prevent the pile from necking. I always required at least 10 feet of head be created before the auger was moved.

A lot depends on the type of soil, how likely it is to cave, and generally how the piles are installed.

The original post discussed a malfunctioning grout pump. I've had that happen on jobs, and it can be tough to tell how well the pump is working by watching and listening. The only way to know for sure if the pump is actually pumping is to stand on the hose while the pile is pumped.

Inspection by an experienced professional should be required for all ACIP piles.

Mike Lambert

 

[qualitypro]

GeoPaveTraffic,
Thanks for your response. I confirmed with the site that the rebar cage of about 26 feet length for the top half of the pile did go in easily. When we reviewed other ACIP data at this equipment area we see that the overall grout factor of 1.39 was much higher than some of the adjacent piles.