Rock socketed section of Pipe pile installation method 2

[TTTKAO]

Hello All,

I am in a project need using steel pipe piles. i saw some topics in this forum, i still have some questions regarding to the rock-socket here. As per the superstructure load and site conditions. There are some recommendations for the piling which i have questions. wondering if can get some advice and opinions from you.
1. "1067mm diameter pipe with 22mm thickness is recommended, the pipe pile is recommended to be driven, cleaned and filled with concrete to the tip of pile. therefore, the piles are modelled as close-ended steel pipe for the analysis"
1)So physically, there is still open-end pipe pile, as plug with concrete at the tip end, closed-end pile will be used for design/calculation only. does my understanding make sense?
2. "the piles for the equipment foundation should be completed as rock-socketed piles. The rock socket length should be defined to resist the additional tensile loading condition and the end bearing resistance that cannot be mobilized without breaking the shaft resistance. Rock sockets with a diameter of 914 mm (150mm smaller than the proposed pipe pile diameter) and a minimum rock socket length of 3 m are recommended for the proposed loading conditions"
1) How this rock-socketed pile will be installed and formed, is it a solid concrete by drilling underside of pipe pile?
2) what's the connection between rock socket and pipe pile, why there is 150mm reduction here? wondering how to transfer uplift load? is this installation consideration?

Thank you!

 

[HTURKAK]

My understanding is ,

1- End plug will develop during pile driving so the end bearing will be similar with closed end pile. However , since the end is open , it will not be displacement pile and wall friction and driving resistance will not be same with closed end pile.

2/1 - I understand that ,the pile will be driven with open end up to the rock level , then the interior will be emtied then the rock drilled from the top of pile with boring dia . 914 mm

2/2 - The rock socket should have reinf . extending to the interior of pipe pile . The uplift will be resisted by own wt . of concrete filled pile and socket + friction developing at rock socket and steel pile exterior surface.

..

He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[SlideRuleEra]

ArcherC - As stated the pipe piles are driven, cleaned and filled with concrete... making them closed end piling that resist loading with point bearing.

Note that the rock-socketed piles described do NOT say that they are driven. The description given is just like the rock-socketed that we have used. The piles are drilled piers, solid reinforced concrete from pile tip to pile butt. A (driven) pipe is used, if needed, to keep the overburden from collapsing into the hole drilled in rock (before concrete placement). Drilling of the rock socket is performed thru the pipe. The pipe may, or may not, remain in place after pile completion, but it is not considered for load support.

 

[TTTKAO]

Hi HTURKAK
Thank you for the sharing and confirmed most of my "guessing", appreciate a lot. I still have a few queries left.

For this item, could you help to explain a bit more. Does reinforced concrete have to be filled to the pile cap? i haven't touch pile design for a while and the pile installation experience is limited. Curious if the socket reinforcement can stop around the bottom of pipe pile and what's the detail will look like to transfer uplift force between socket and pipe pile if this is possible? the reason why i have this idea is because the geotechnical report says " The structural designer should also check the required pile reinforcement that would likely be required to transfer the pile cap forces along the pile and rock-socketed section" but i can't imagine how the load transfer if the reinforcement stop in the middle of pipe pile

Thank you!

 

[TTTKAO]

Hi SlidruleEra,

Thank you for the sharing, and appreciate a lot. I used to understand in this way, but there are some points still can not convince me.


1. 22mm thickness wall is suggested in the report, it seems too thick to a dilled pile caisson shell only.i think they should call this piling as concrete pile not pipe pile if the pipe won't share any load.
2. From my common sense and design/construction knowledge, i think the report is recommending to use concrete filled pile with 3m concrete rock socket. but i am confused they are using term "pipe pile". not mentioned to need fill the concrete to the pile cap. maybe this is common knowledge to do in this way or leave structural engineer to design it...

Thank you.

 

[SlideRuleEra]

...1067mm diameter pipe with 22mm thickness... to be driven...

The pipe may be thick to be used as a caisson shell, but needs to be thick to withstand the high force applied if impact pile driving is used.

 

[HTURKAK]

I do not look to the forum everyday .Moreover , we are at very different time zones .( i am at UTC + 7.00 time zone)
I will try to respond to your querries based on up to my knowledge and experience ;

- You did not provide a lot of info. here. If the pile length short enough , if you need more compression resistance filling reinforced concrete to the pile cap is an viable option. If you need uplift resistance , and you have substantial pile length ( say more than 20.0 m) the socket reinforcement can stop around the bottom of pipe pile and the detail would be providing welded shear keys at interior of the pile .

- In order to get more info , I will suggest you to look ,
- NCHRP, Rock-Socketed Shafts for Highway Structure Foundations,
- Rock Anchors By Little JOHN

You may look API RECOMMENDED PRACTICE 2A to get the concept of welded shear keys at interior of the pile,

He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[TTTKAO]

Hi HTURRAK,
Thank you so much for the further explanations, The project just started, actually i am looking for possibilities for the solutions and curious design basis/reference for possibilities. you gave me a very clear and detail advice absolutely. Amazing, thank you for your time again.

Regards!