Pile Capacity from a Excavator Driven Hydraulic Hammer

[mmartens]

I am trying to determine / calculate the capacity of a pile that is being installed with a hydraulic hammer attached to an excavator. The hydraulic hammer has
a manufactures power rating of 3577 Joules operating at 320 to 600 hammer blows per min. the operator is pushing down on the hydraulic hammer with all the added weight of the excavator (i.e. the tracks are in the air). The pile is being penetrated at a rate of about 40 to 50 mm per min.

Any Thoughts?

 

[DRC1]

hydraulic hammers are similar to double acting hammers. Generally they are rated in equivilent foot pounds. I have not seen an excavtor mounted one. The rate 320 to 600 bpm is very high. Are you sure this is not a hydauliclly driven vibratory hammer? And why is the excavator pushing so hard on the pile? It seems it risks damage to the machines and must make maintaining pile alignment difficult.

 

[Zambo]

DRC1 it does sound like a backhoe mounted vibro. I have often used these machines for driving sheet piles and H sections into clay soils, but only for temporary works.

mmartens what type of pile are you installing? What depth are you driving to?

 

[mmartens]

Hi DRC1 and Zamdo

It is a hydauliclly driven vibratory hammer on an excavtor. The piles are just 6 inch pipe pile with a pointed end. The depth is about 4 meters to 6 meters or longer if needed the material is mainly clay to a soft sand stone or some times just clay or hard sand. I am looking for a capacity of 10 kN to 40 kN depending on the pile. I am wondering if the capacity can be calculated using hydauliclly driven vibratory hammer mounted on the excavtor. The reason that we use this (the excavtor)is for quick site construction with only about 10 to 20 piles needed in remote locations.

 

[PEinc]

If your pile design capacity is less than 40 Kn (about 9 kips) why not load test a pile by jacking against the underside of the excavator? This would be fairly easy and would not take too long. You would need to set up some dial gages and get a small hydraulic jack to apply the load.

 

[Zambo]

PEinc I like your idea - but the next question will be how long to apply the force from the jack and what is the acceptance criteria.

Why has the pipe got a pointed end. I think with the vibro you will have more success driving the open pipe. Just now your pile penetration of 40-50mm per minute is extremely slow and I doubt it is doing your backhoe any good.

 

[PEinc]

Look at ASTM D1143 for a Quick Pile Load Test. Who designed the piles? What is their testing requirement?

The pile is very small in diameter. It is probably pointed for easier driving and tip protection. Do the piles have to be filled with concrete or grout after they are driven?

You could also drive the piles with a small impact air hammer. You could stick the piles with the vibro, then drive them to capacity with a small impact hammer hung from a small crane. You could even "guestimate" the pile capacity using a dynamic pile driving formula, if that is acceptable to the designer.

 

[mmartens]

The piles are used as under ground pipe support and meter station supports. The pointed ends are for easier driving and tip protection there are not filled or grouted.

The pile penetration at first is very fast and them slows to 40-50mm per minute and then even slower but never really stop.

I am thinking if I know (estimate) the excavator load on hydauliclly driven vibratory hammer, knowing the spec. of the hammer and knowing the pile penetration for time. I should be able to estimate the capacity of a pile.

I do not know the equation for estimating "guestimating" the capacity using a dynamic pile driving formula.

 

[Zambo]

mmartens

if you are stuck with the vibro and are not planning a change to an impact hammer then as far as I know there is no pile driving formula.

The piles are being used as underground pipe supports - does this mean that the piles are spread out over a large area? This means the soils will change and piling to length is not reliable.

Assuming the 2 statements above are correct then I think you should follow PEinc's advice on load testing using the backhoe.

 

[DRC1]

There are sme formulas to estimate pile capacity from a vibro. Bowels lists them in "Foundation Design" however thes are very crude and closer to a guess than an estimate. It appears that the vibro yuo are using may be small and as such is not providing enough vibration at the tip. I think you may be better setting the pipes as best you can with the backhoe and then follwing behind with a 50 ton rt crane. I would use a vulcan 01 impact, flying or hanging leads, and a wave equation bearing capacity. You will probably find this to be a much more efficent system, not even considering the wear and tear on your backhoe and vibro.

 

[eric1037]

Why not use soil boring information to calculate capacity? Just use a higher factor of safety if you can't use a load test. As DRC1 stated, I wouldn't trust the equations in Bowles book for vibratory hammers.

 

[Panars]

I think either the load test with the excavator or the calculation from the soil boring is the way to go. But, if you are determined to go another way, then I would point out that the latest version of GRLWEAP will perform a wave equation analysis for vibratory hammers. The analysis will calculate a graph for pile capacity versus pile penetration rate for your particular vibratory hammer. I have never used it myself.

 

[PEinc]

Panars, you are correct. However, doing a WEAP requires some engineering and the GRL program. I would either jack against the excavator or use an impact hammer with a driving formula. These two options may be the cheapest available.

People can talk about the inaccuracy of the driving formulas but remember, up until recent years, that's how pile capacity was determined, in addition to using static load tests.