Precast concrete pile + weathered rock / How to make a pile foundation in proper way? 1

[LonelyDeer]

Hello.
I've tried to find an answer during hard internet search (without result). I hope you'll help me.
Input:
1.Pedestrian bridge
2. Soil conditions ( 1m of sand, 4-5m of expansive clay with high expansive strain, weathered rock - argillite),
3. Therefore - pile abutment (flood is common thing in this place, so clay will expand -> we need to go further to the rock)

Design process:
First idea - boring piles d=600-800mm was banned ( too expensive, uneducated workers (Eastern Europe) + too hard to control pile quality). Second idea - precast concrete driven piles (rectangular 350x350mm). But here we have a problem.
Rock layer have rather steep angle, so we can't guarantee reliability of pile's end bearing, because during driving pile's shoe can slip down and pile will go out of it's normal way.
Things may go like here (except welding joints, our pile is solid - one section)[Pile Design and Construction Practice, sixth ed., Tomlinson, Woodward].

Third idea - drive pile (rectangular) in pre-bored hole (d=400mm - bore 0.5-1m in rock) and then put a low-class concrete between pile and soil.
Or fourth idea - drive pile (rectangular) in pre-bored hole (d=300mm - bore 0.5-1m in rock). I'm afraid that in that case pile's end won't completely enter in rock or corners of pile's end will shear, but on the other hand rock is rather weathered.

And here is my question. Does anybody knows anything about such thing in practice (book, article)? Or some help in terminology, how this method called in world practice? Or maybe somebody can tell me about proper way to create a reliable contact between rock and pile.

Thank you.

 

[oldestguy]

Do you have well drillers in the area? For the light loads, say two per abutment, how about two cased wells to rock each end with a "rock socket" drilled well into rock. Reinforcing steel goes well into that socket and then fill with concrete. Only if necessary (for saving pipe cost) pull the casing slowly as concrete is placed.

 

[EireChch]

First idea - boring piles d=600-800mm was banned ( too expensive, uneducated workers (Eastern Europe) + too hard to control pile quality)

Why do you need to use 600-800mm dia? What are your loads/span? If it is a pedestrian bridge (i.e. not that heavily loaded) can you get away with 450-500mm dia bored in to rock. Substantially cheaper than 600-800mm dia. Also, if you have a good site engineer you can control the quality. If it is just a bridge then there cant be too many piles (depending on span etc)

Second idea - precast concrete driven piles (rectangular 350x350mm). But here we have a problem.
Rock layer have rather steep angle, so we can't guarantee reliability of pile's end bearing, because during driving pile's shoe can slip down and pile will go out of it's normal way.

How steep is the dip in your rock, do you have levels of top of rock to work out a gradient. IMHO, it would have to be very steep before you could consider the pile sliding down the top of rock? I have never encountered such a problem so maybe some who has can chime in.

Third idea - drive pile (rectangular) in pre-bored hole (d=400mm - bore 0.5-1m in rock) and then put a low-class concrete between pile and soil.

If youre going to bore with of d=400mm and 1m into rock why not fill it full of concrete and it can be your pile!?

 

[LonelyDeer]

oldestguy, thank you for advice. I'll consider it.

EireChch , i've forgot to mention about seismic activity with design intensity 9.0 (MSK-64), so my main problem is seismic case. Span - 35m, two steel flanged beam with steel deck, with 4 piles 600mm diameter we have 41.4 ton on pile's end. Argillite have design resistance R=1.5MPa (when it dry R=6.8 MPa, but in our case it's resistance decrease in water, so things are so bad).
We don't have good site engineer, cause this work will make local subcontractor. Try to imagine dumb man with great felling of self-importance, without proper education, an you'll understand me. We've worked with them (awful experience), but corruption + nepotism in local administration, an here we are now with the same subcontractor.
We just want to make things easier to construct, with so many point where they can fail as we can. I'm fully confident only in drillers work skills (they are from other firm).

Angle of our rock layer is about 16-20 degrees.

If you're going to bore with of d=400mm and 1m into rock why not fill it full of concrete and it can be your pile!?

Same reason, we doesn't trust to subcontractor. We can't control quality of concrete on site (precast piles are from good manufacturer).

Than you, for your reply guys. My problem on work now is "How to drive piles to rock and not to break them and not to slip down". If you can refer to any kind of source with information about "driven pile + rock", it will be appreciated very much.

 

[SlideRuleEra]

...during driving pile's shoe can slip down and pile will go out of it's normal way.
We just want to make things easier to construct...

Instead of a pile shoe, perhaps a driven precast concrete pile with a composite H-pile, including an H-pile point:

Then the pile installation is "routine" pile driving.

Is the 16-20 degree slope measured from horizontal or vertical? The above suggestion should work for horizontal angle... not for vertical angle.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[oldestguy]

In my experience if the contractor doesn't follow some plan or specs, he doesn't get paid. Can you withhold payment until the job is done right?

 

[EireChch]

SRE - thats what i was getting at too, i would think that the could be driven down to rock with a slope angle of 20degrees from horizontal.

They would not get the socket into rock as a drilled pile would but do the loads require a rock socket. Rock socket is definitely good practice/norm but might not be essential.

 

[aeoliantexan]

I like SlideRulEra's solution. An alternative might be either steel H piles or steel pipe with special points such as those marketed by Associated Pile and Fitting Co. They have a "Rock Injector Point" for H piles intended to penetrate the rock and hollow cylindrical points for pipe piles that would allow drilling a rock socket below the pipe if necessary. One advantage to pipe piles is you can look down them and see whether they are curving off to follow the rock surface.

 

[PEinc]

Weathered rock was originally mentioned yet the responses and details being shared seem to be applicable to hard, pinnacled bedrock. Are we talking apples and oranges?

http://www.PeirceEngineering.com

 

[Okiryu]

LonelyDeer, we use pre-cast prestressed concrete piles with Pre-drilling thru the rock layer to create a rock socket. Then we inject grout into the borehole, then insert the pile. So no need of pile driving...This method is typical here in Japan.

 

[LonelyDeer]

Thank you, guys, for all your help. I really appreciate it. For reasons beyond our control, we had to leave this project.
Wish you good holidays.