Grouted Helical Pile Capacity/Required Depth 1

[AndBre44]

Looking for some general information from those much more educated on the topic than myself: I have a job site where we have poor quality soils, so we're using helical piles to support the building load. The piles were expected to only go down to about 20 ft before reaching their intended sandy stratum, but are instead going down no less than 40ft, and in some locations boulders are being encountered causing us to abandon the piles in place.

As an alternative, I'm looking to specify a grouted helical pile as opposed to a standarded drill helix, but want to be sure I know the right direction to give the contractor before specifying.

I understand that the use of a displacement plate is what effectively creates the grout column, my question is what would be the means of understanding if it meets expected capacity? For example, with typical helical pile installation I know that when the pile reaches its specified torque that I know that equates to its compressive capacity; are grouted piles measured the same way in-field as it is dug down? Or will they only know the piles capacity if a load test is conducted?

The hope/goal is that they can use a grouted helical pile to reach the same intended capacity but potentially at a shallower depth. Any advice/experience on the topic would be greatly appreciated.

As an EIT, I'm open to being wrong now if it means being right when it counts.

 

[PEinc]

Call Steve Gencorelli, P.E. at DANBRO Distributors (215)271-7700.

http://www.PeirceEngineering.com

 

[BridgeSmith]

Maybe I'm not understanding configuration of a grouted helical pile, but if it's what it sounds like, I'm not seeing the advantage of that over a reinforced drilled shaft (caisson) or an augercast pile.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[EireChch]

I strongly agree with BridgeSmith. I cant see a benefit of using helical pile, grouted or not if going to more than 40.

The issue of hitting boulders is my biggest worry, not that your bearing layer is deeper.

You need to do a bored pile to ensure you penetrate and boulders.

 

[PEinc]

The advantage? Helical piles or piers will be much cheaper than drilled shafts or augercast piles. If there are boulders, rock or very dense soil layers; helicals may not be the best foundation choice. This emphasizes the importance of a thorough soils investigation. Pick the right "tool" for the given ground conditions.

http://www.PeirceEngineering.com

 

[CaryGAPE]

Depends on the scope of the job and how much your are leaning into the friction capacity from the grout column. If leaning into it very hard, and scope justifies it, would likely justify a load test. If not, sometimes use historical bond values from similar sites areas if enough data is available.

As far as advantage of helical piles, I would assume that has already been addressed as not enough information has been presented to why helicals were chosen over say drilled shafts or augercast. Reasons were likely one of or some combination of low mobilization costs, small equipment or low overhead advantages, speed, no vibrations or no spoils.

If you would like to discuss in more detail, you can call me at 470-226-2014, Foundation Technologies. Distributor for Chance Civil Construction products.