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Driving Timber Piles with Excavator Bucket
9

Driving Timber Piles with Excavator Bucket

Driving Timber Piles with Excavator Bucket

(OP)
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.

RE: Driving Timber Piles with Excavator Bucket

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

RE: Driving Timber Piles with Excavator Bucket

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

RE: Driving Timber Piles with Excavator Bucket

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!

RE: Driving Timber Piles with Excavator Bucket

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.

RE: Driving Timber Piles with Excavator Bucket

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

RE: Driving Timber Piles with Excavator Bucket

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.

RE: Driving Timber Piles with Excavator Bucket

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?

RE: Driving Timber Piles with Excavator Bucket

(OP)
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.  

RE: Driving Timber Piles with Excavator Bucket

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

RE: Driving Timber Piles with Excavator Bucket

(OP)
Timber piles will be embedded in the wall footing.

RE: Driving Timber Piles with Excavator Bucket

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.

RE: Driving Timber Piles with Excavator Bucket

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.

RE: Driving Timber Piles with Excavator Bucket

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.

RE: Driving Timber Piles with Excavator Bucket

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.

RE: Driving Timber Piles with Excavator Bucket

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.

RE: Driving Timber Piles with Excavator Bucket

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

 
      

RE: Driving Timber Piles with Excavator Bucket

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.

RE: Driving Timber Piles with Excavator Bucket

Understood. He then needs to treat the bucket as a drop hammer and use one of the driving formulae. Try the ENR forula which was designed for use with wooden piles. A graph as the pile is driven is required to determine the so called set. A capacity can then be derived.

I would check the depth of pile in the ground to determine if it has reached the sand layer. This can be readily done from the borings.  

We must remember that pile design should not be undertaken by just looking at one approach. In the end we need to apply judgement to the information we obtain which should be based on observations as well as the use of the varied relationships that exist.

RE: Driving Timber Piles with Excavator Bucket

VAD - 3of12 has told us the following:
25' timber piles
15' of soft clay & peat
then 10' of sand

What is missing is how far did the contractor push the piles down? If it is to the sand (15'), then cutoff the excess pile length - I believe this is a real problem.

If it is the entire 25' (10' embodiment in the sand), perhaps your point is valid.

From my experiences as a bridge contractor, I expect the former case is more likely. If 3of12 can confirm the details, I'll offer my reasons.

www.SlideRuleEra.net idea

RE: Driving Timber Piles with Excavator Bucket

I don't think you can free-fall a hydraulic boom with the hoe bucket.  Therefore, I don't think you can calculate the energy to the pile - which brings us back to the original question and answers.

RE: Driving Timber Piles with Excavator Bucket

You can impart much more energy to the bucket than the machine can repetitively take.  Movement will become sloppy with all the slack in the connections.

RE: Driving Timber Piles with Excavator Bucket

If you have a pressue indicator you can se your hydraulc pressue  in vaarious parts of the system and compute your crowd force. I don't know if  this is possible on a 321. But again, when he presses down on the pile and raises his sneakers off the ground, the machine is essentially a simply supported structure, one can calculate the applied load to the pile. Sice the machine probably weighs around 21 tons, and the center of gravity is favored slightly to the rear, I would expect ultmate capacity to be about 20 tons. Since this is not a traditional load test, I would use an FS of at least 2.5.
Good luck

RE: Driving Timber Piles with Excavator Bucket

You could check what DRC1 said, but I seriously doubt you would be able to get what it takes, even if the bucket was crowded.  You would want to fill the bucket anyway...

RE: Driving Timber Piles with Excavator Bucket

Amazing!  We seem to be spending a lot of time trying to figure out how to do something the hard way and inaccurately.  It's just as easy to determine the pile capacity correctly using a jack and the hoe as a jacking reaction.

RE: Driving Timber Piles with Excavator Bucket

If the hoe is big enough...

RE: Driving Timber Piles with Excavator Bucket

A Caterpillar 321C/LCR weighs 52,911# per Cat's web site.  A very fast guesstimate is that the foundation wall carries about 5 KLF.  At 5' c.c, a timber pile would have a design load of about 25,000#.  There's pretty good chance the hoe may be heavy enough.  However, we do not know the pile design load.

RE: Driving Timber Piles with Excavator Bucket

Then there's the moment arm, unless you're going to balance the hoe on the tip of the pile...

RE: Driving Timber Piles with Excavator Bucket

It sounds as if these timber piles are structural in nature. If that is the case, the minimum tip is only part of the equation. You may be able to calculate the hoe as a static test but the figure will be a SWAG. If the contarctor insists on using the excavator he could use something similar to this and still be able to prove the capacity of each piling.
 http://youtube.com/watch?v=HJOoiIN5O7s

RE: Driving Timber Piles with Excavator Bucket

I think this is a crude way to drive a pile.  The various views all seems to make some sense based on their perspectives. Most likely I think this pile was designed for end bearing, and a minimum elevation was specified for the bearing stratum.  Once this elevation is achieved, the bearing capacity 'should' be fine, but that is not always the case.  Secondly, as someone pointed out, if this pile was designed for skin friction, I believe there is a risk for lateral movement of the pile during driving which could decrease the skin friction.  Thirdly, a two-story structure is expected to impose relavely low bearing pressure (but negative skin friction should also be considered, as pointed out earlier) and just the fact that the excavator could drive the pile no further, there could be enough capacity for such the pile for this structure.

Now in reference to determining the load on the pile I think the the first response by DCR1 was right on point.

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