2 7/8 dock piles 3

[Dustyhohmann]

thread256-110287

I was searching on google for some info and came across this thread, so I thought I would look for some help here. I am located in central Texas on lake LBJ, and work in boat dock construction. The normal around here is to drive 2 7/8” pipe using pneumatic hammers. We use a 110lb hammer. We drive through sand then into what everyone says is a granite gravel. Everyone try’s to drive the pipe to complete refusal. I have driven pipe from 5’ to 65’ deep using this method. But I was curious if there is away to figure out the blows per inch for refusal using these smaller hammers, and how much skin friction there might be. The reason I ask is because we build two story boat docks with concrete decks, so some of these piles hold about 3500lbs on them, which I don’t feel like is that much. There is no construction code here for thee boat docks, and I have never seen a engineered plan either.

Thank you for any help you can provide.

 

[PEinc]

There is much more to this than can be easily answered in an on-line forum. I recommend that you hire a local geotechnical engineer who should be able to give you guidance for obtaining the required pile capacity for a particular project and known soil and rock conditions. Piles don't always need to be driven to refusal.

http://www.PeirceEngineering.com

 

[Lomarandil]

Agreed, piles do not always need to be driven to refusal.

Now, I don't know how much it costs you to drive pile, or how many feet you drive per year... the economics may or may not justify hiring a geotech engineer for an analysis & investigation. But that is your best bet -- and most geotechs aren't that expensive. Find someone local -- they'll know that geology from their other projects.

If you're doing a lot of these, load testing might work. If you're technically minded, you could dig into NAVFAC DM-2 or Army Design of Pile Foundations Manual. Keep in mind that most of these pile foundations get a factor of safety of at least 3 in design, sometimes more.

----
just call me Lo.

 

[SlideRuleEra]

Dustyhohmann - IMHO, just keep driving the same way you have been. The laws of physics for a 110 lb. hammer will override geotechnical advice.

The hammer (ram) should be heavier than the pile. If the 2 7/8" diameter pile is nominal 2 1/2" steel pipe, schedule 40, the pipe weighs 5.8 lb/ft. At pipe lengths greater than 19 ft., the pile weighs more than the ram. As pile length increases beyond 19 ft., energy transfer from ram-to-pile-to-soil becomes increasingly blurry which will strictly limit the value of even the best geotechnical advice.

That is the simple (physics) reason. There are other, more subtle physics reasons that concern the blow rate and ram's fall distance than limit the value of "small" hammers.

You can make good use of geotechnical recommendations... but to do so, the ram needs to be much heavier than 110 lb.

http://www.SlideRuleEra.net

 

[Settingsun]

Are dynamic driving formulae any less suited to small piles like this than usual? eg Hiley, Washington DOT, Gates, Danish, Janbu. I know they're not fantastic in any case, but wondering whether they're less so at this pile size.


Dustyhohmann, what's the hammer's rated energy?

 

[Ron]

Exactly, SRE! That's why a casing hammer is 300 lbs. Maybe he should consider using a casing hammer. Would be good to about 50'.

But...he'll also be driving long piles since he'll probably punch some through stuff that currently refuses.

 

[Dustyhohmann]

Steve-

It weighs 109lbs and delivered 930 blows per minute. It only raises about 2” before it falls again. That’s all I can find about them. It’s the normal tool around here for the past 30yrs or so. I have rarely seen a actual pipe driving rig.

There is around 10 dock builders around here all using the same method, except one, they have a excavator on a barge with a sheetpile driver(vibration) and they are still doing the same depths as us, if not less.