Driving Timber Piles with Excavator Bucket 9

[3of12]

I am working with a contractor in a development who prefers to drive timber piling with the bucket of his excavotor. He has a Caterpillar 321C/LCR. It would be helpful to know what kind of energy he is imparting on the 12" by 25 foot timber pile. He typically drives the pile until he gets enough resistance to make his machine stand up. This is his "field test" I guess you could say.

If he is driving the piles with 3 to 5 foot swings with his bucket, could we come up with some magnitude of force this thing is imparting to help us arrive at a capacity figure for the pile? Any thoughts out there? Thank you for the interest.

 

[DRC1]

A 321 is not a big machine. I would guess it weighs around 20 tons. It is hard to figure how much force he is putting into the bucke because that is contorled by the operator. Like trying to measure how hard someone is swinging a hammer. However when he stands his machine up you have a simplysupprted structure with the front of the crawlers as one support and the driven pile is another. By looking at the Cat manual and making a few guesses abot weight distribution, you can solve for the reaction in the pile

 

[SlideRuleEra]

See the comments at thread256-168264
particularly those by PEinc and Panars

http://www.SlideRuleEra.net

 

[jdonville]

3of12,

Why is the owner letting him do this?! It's your job as the engineer to educate the owner about the risks that he may be required to assume by not requiring the Contractor to use a proper hammer. The excavator - and it's not really that big as DRC1 says - will impart lateral forces on the pile that may prejudice the development of skin friction after "driving" and/or damage the pile tip.

Jeff

 

[Panars]

SlideRuleEra
I don't think my comments in the thread you referenced are relevant. That thread had to do with driving sheet piles with an excavator mounted vibratory hammer. This contractor isn't using any pile driving hammer; he's whacking the timber pile with the excavator bucket!

 

[PEinc]

Panars,

I do not believe that the referenced thread addressed sheet piling. The original poster said that the piles were 6" pipe piles. Both of our comments in that thread are applicable.

Good reference, SlideRuleEra.

 

[eric1037]

I would also worry about damage to the butt end of the pile.

 

[Panars]

SlideRuleEra and PEinc-

You are right about the type of pile in the referenced thread; my mistake. I think your comment about load testing the pile with the excavator is appropriate to the current thread. However, I don't think my comment about doing a wave equation analysis applies to this thread. I don't know how you would figure out the energy from a dropping excavator bucket.

3of12 does not say what kind of soil the timber piles are being driven into. If the soil exhibits a lot of setup, this may be why this method has worked for the contractor in the past.

 

[Zambo]

This is a bit ridiculous. It may be that the contractor can hammer down a pile with the excavator bucket - that will depend on the soil conditions. But what are the piles for? Are there any load bearing requirements?

 

[3of12]

The timber piles are intended to support concrete wall footings for a 2 story, single family homes. Substantial strata (medium sand, 10 feet thick) is overlain by 15 feet of soft clay and lenses of peat. Thanks to all for your comments.

 

[LCruiser]

Shoring for pouring the footings, or be imbedded in the footings, or what?

 

[3of12]

Timber piles will be embedded in the wall footing.

 

[rockiologist]

I have encountered a simlar situation with a competitor recommending using timber piles in similar condition. Now they are being sued to due to settlement. Be careful.

 

[LCruiser]

I agree with rockiologist. If this is not just for construction purposes but is to be permanent, I would not allow the contractor to just beat on the end of the piles until they didn't move anymore.

 

[SlideRuleEra]

Concur with rockiologist and LCruiser.

http://www.SlideRuleEra.net

 

[LCruiser]

If he's a responsible contractor he bid it to bring in a driver. It sounds like the supt is trying to pull a fast one - he could "finesse" a large chunk of profit - at the expense of the project. Just tell them no and see what happens. Keep us posted.

 

[civilperson]

If the vertical load/pile is less than 5 tons then the amateur method described of pile installation will propably suffice. Any lateral loads or higher design capacities should be checked with a pile test. That will give assurance of ultimate capacity which can be divided by FS.

 

[LCruiser]

What civilperson says is true - an alternate from bringing in a piledriver could be to increase the number of piles. However, don't let him skimp on this. It could come back to haunt you.

 

[VAD]

I have read the responses to this thread and would like to know what is so wrong if the excavator can drive the piles through the peat and have them embedded in the sand.

The Contractor typically does this as is understood. Has there been problems with the buildings constructed so far or is it too early to say.

If I can place a pile to the desired depth by what ever means what is so wrong. Who care about the energy imparted to the pile. here I am confident of the soil stratigraphy below the pile base and I am also confident that there is no further settling layer below the base.

I think the Contractor has a bit more sense than we give him credit for. Let us think about it, he is driving through peat. There are soils in some parts of the world that it only takes the weight of the hammer resting on a wooden pile to send it down to the bearing layer. Buildings resting on those piles have survived well.

Who cares about the set and energy if we can get where we want. Intelligent pile design is first done through careful examination of the soil profile followed by what it takes to get the pile to the depth to which we want.

We are only designing for a two storey building. What is the fuss. How many piles is he using versus the load that will be transmitted to the foundation.

I think thatv you have a smart contractor for the given ground conditions

 

[PEinc]

VAD,

The original question was about how much energy was being applied to the piles during driving with the hoe bucket. So far, no one has answered that question.