Practical way to get piles to rock?

[oldestguy]

For a single span short bridge, normally built by an ordinary bridge contractor, with simple pile driving capability, I have a question about what it practical. Site is in glacial country of Wisconsin.

The site has loose sand and silt to 60 feet and then a dense deposit of sity sand and occasional cobbles. However, in that zone and for considerable depth below there is artesian pressure of considerable magnitude. The fear is that piling founded in the dense zone will lose side friction and end bearing and settlement will occur. This has been known to happen at other sites in the state

We would like to get pling down to rock, which is at 100 feet. The usual loadings have been 40 to 60 tons per pile.

The usual contractors have pile driving equipment for say 50 ton H piles of 10 and 12 inch size, with welding capability, due to crane boom limits, etc. However, specifying piles have to go to rock, say by driving, may not be feasible.

Can jetting be done by some means that does not require a much taller crane boom?

On one job I know of a test boring was left with casing and a T fitting with horizontal discharge section, that apparently relieved the pressure. Maybe this is the answer, but local water regs dept may not permit it.

Would vibration methods do the job?

A heavier pile section driven to 100 tons? Any ideas?

 

[jdonville]

oldestguy,

You would likely need a heavier pile section just to avoid overstressing during hard driving. You might even need to retap if you hit refusal criteria. With cobbly soil in the profile, it will be a royal pain to drive to rock, though.

Drilling to depth through cobbles will also be a rare joy with the added fun of the artesian pressures.

I will ask around and see if some of my confreres can offer some positive advice.

Jeff

 

[hokie66]

As you detailed, there are a lot of problems and perhaps some unforeseen difficulties in driving piles to rock in your situation. I would not rule out founding the piles above the artesian zone. Expanded base driven cast in situ piles (Frankipiles) founded in the looser material might be the solution.

 

[vulcanhammer]

If you're going to drive to rock, you should seriously consider pile points. An excellent reference on this is found at

http://pilepoints.pilebuckinternational.com/

I would avoid using a vibratory to drive a pile to rock unless you're prepared to switch to an impact hammer before you actually get to rock (and are always sure where that point is!) The kickback from the pile toe beating on the rock will destroy the high pressure piston hydraulic motors common on the larger vibratory hammers.

http://www.vulcanhammer.net

http://www.vulcanhammer.info

 

[DRC1]

Trying to auger through the cobbles is slow and difficult, not to mention expensiveVibrating piles through the cobbls will also be difficult. You should be able to get decent bearing capacities in the upper sand and silt using 14 in. 3/8 wall closed end pipe. Although opinions vary, I would recomend filling with concrete & bar. Contractors who drive H-piles should be able to drive pipe. Since capacities may be lower, you may need a few more piles. With this method, you would be able to utilize local contractors and avoid obstruction costs.

 

[PEinc]

Maybe a single span short bridge with a difficult foundation should not be built by an "ordinary bridge contractor, with simple pile driving capability." Think about it. A contractor needs to be qualified and experienced in the type of work that needs to be built.

 

[MiketheEngineer]

Practical way to get piles to rock?

Play Rock Music....

Just HAD to say that!!