Driving timber piles into pre-bored rock

[Settingsun]

Does anyone have experience and guidance for driving timber piles into pre-bored. rock sockets? The rock is sandstone, medium strength not too far below top of rock. The piles extend above ground as cantilevers subject to lateral loads. There isn't enough sand over the rock to achieve stability of the pile without going into the bedrock.

I've come across an old specification which refers to this method of installation but is a bit light on detail. It's not clear whether the pre-bored hole is smaller than the pile or by how much.

I assume you'd have to trim the pile toes to suit a standard auger size?

The piles are hardwood with bending strength of 55 to 80+ MPa and compression strength of 40 to 70+ MPa (characteristic ultimate values per design code).

 

[jdonville]

Would be a lot more practical to place a pile in a rock socket and concrete around it, IMO.

My state DOT still has test driving of steel piles placed into rock sockets as a thing; I think it's dumber than a box of rocks - why risk damaging the pile?!

 

[geotechguy1]

Why not just drop the timber pile down the hole and pour concrete around it

 

[Settingsun]

Concreting into oversize hole was the original detail but driving into a snug hole has been suggested to simplify. The piles are in water so need temporary liner to keep the hole open and then underwater concreting. I can see the attraction but don't have personal experience with the method.

 

[jdonville]

What is being supported? Why timber pile? Why not use a drilled shaft into the rock (you would likely need to anyway to make the core) and extend it up thru the water?

 

[MTNClimber]

Driving timber piles down to bedrock is risky since it will easy to damage the pile. I would of just grouted a steel pile into the rock socket while you had the equipment over the hole. I'm not saying it can't be done but it just seems like not the best method. Is there any overburden at all? Can we get more details about the structure and subsurface conditions?