Maximum Pre-Drill Depth for Driven Piles 1

[AlexH15]

Does anyone know if there is a maximum pre-drill depth for piles? I assume there has to be some limit, but I cant find any specifications for this.

 

[jayrod12]

Is there any uplift on the piles? Are they relying on skin friction or bearing? I would assume bearing. If there's no uplift, then I would say no however at some point you'd be concerned about the lateral stability of the pile. If there's uplift, then yes you want to minimize pre-bore because you're relying on a length of skin friction.

 

[MTNClimber]

If you mean limitations from equipment then, yes there are limitations. Some pile driving contractors have a fixed lead rig with a continuous flight auger attached to it. Limitations of that system would be the height of the leads would control the auger length. Another way I've seen predrilling conducted is using a tieback rig to break up obstructions. In this case, there isn't a limitation of length but a limitation on the diameter of the hole they can drill. I'm sure there are different methods out there that I haven't seen. I'm sure some have even used a caisson rig to pre-drill. Obviously mobilizing a different piece of equipment (and sometimes different crews) means more cost for pre-drilling, so be aware of that.

Since pile driving contractors all have different means and methods, you should talk to the ones in your area. I've found that they love talking about their equipment and capabilities.

 

[SlideRuleEra]

I assume there has to be some limit, but I cant find any specifications for this.

There won't be a specification, there are too many variables, but there are some general guidelines:

It's common to predrill through fills and embankments so that actual driving begins at natural ground elevation.

On projects where pile driving vibration may damage nearby existing structures and piles are point bearing, it's common to predrill to nearly full depth. This minimizes the time needed for actual driving.

If there is hard material or rubble at a shallow depth, predrilling through this layer (then stopping) allows the pile to then be driven to obtain sufficient embedment.

If an oversized hole is predrilled, the hole is to be backfilled with compacted granular material (exactly how to ensure this is accomplished on a deep predrilled hole mystifies me).

A predrilled hole is never the full depth of the piling. The objective is to drive the pile at least some distance... not to just "drop" a pile in a hole and backfill it.

A predrilled hole smaller than the pile can be used to speed up the driving process. How deep and what diameter is a project-by-project joint decision by the Engineer and Contractor.

Predrilling is typical for displacement piling (wood & concrete) not steel piling.

There are plenty of situations where predrilling is not appropriate and should not be allowed.

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