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.

 

[VAD]

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.

 

[SlideRuleEra]

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.

http://www.SlideRuleEra.net

 

[PEinc]

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.

 

[LCruiser]

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.

 

[DRC1]

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

 

[LCruiser]

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...

 

[PEinc]

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.

 

[LCruiser]

If the hoe is big enough...

 

[PEinc]

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.

 

[LCruiser]

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

 

[ShawnR]

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

 

[Riggly]

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.