How to connect timber piles and concrete piles? 3

[dachenglee]

I have existing timber piles, and I want to extend them with concrete piles as 2-story house foundation. How can I connect timber piles and concrete piles? Fasteners?

 

[dicksewerrat]

I wonder why you don't want to use more wood piles. aalso are these end bearing or friction?

 

[dachenglee]

Thank you for the response dicksewerrat. There is an existing 1-story set on those timber piles. The owner wants to break down the old house, and build a double size 2-story house. He asked me to keep those existing timber piles for the proposed house. It is a 30 years old house; so, we don’t have any data about the existing timber piles (depth, end bearing, or friction). Of course, we will do the bearing capacity loading test on the existing piles after the old house breaking down. We design to use concrete piles under the extend building area; also maybe add some concrete piles under existing building area if necessary. That is why I would like to know how to tie a wood pile to a concrete pile.

 

[Focht3]

That's a really bad idea!

You don't know the condition or length of the existing piles. Personally, I only allow the foundations to be reused when the new structure's loads are essentially identical to the old ones.

And I haven't even talked about the danger of mixing foundation types beneath the same structure!

Think about it: what are the consequences to the building - and you - if the two story home settles unevenly?

Its a bad idea. A very bad idea. Put in all new concrete piers, or walk from the job. Unless you really like the company of lawyers and enjoy spending lots of time in depositions and trials...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[CSEllc]

I agree with Focht3...............Have fun getting to know the lawyers.

The way I see it is you have a few options....
Option #1: remove the existing concrete foundations. Install new wood piles, as if the existing pile are not there. This option basically "more than doubles" the number of piles needed, since you will be working around unknown pile locations. It will also require a significant amount of "field" work by your office.

Option #2: Remove the existing concrete foundations and "load-test" the existing piles. At that point, you need to add piles as required. Desig the new foundation, grade beams, etc. This will give you the allowable lods tro the in-situ piles. and could also find any broken or unacceptable (below capacity) piles that might be in the ground.

Option #3: Leave the the existing piles and grade beams in place. Install new piles to reduce the span of the grade beams and reduce the loading to the existing piles. This option is also very risky since you are basically accepting whatever is in the ground. It might also have you meet the lawyers similar to your original idea.

I would recommend eistrher option #1 or @2. Either way, it will be an expensive foundation.

Focht3.........any comments? I know you must have at least one or two on my response. CSEllc

 

[Focht3]

I concur. I prefer Option #1 - as I suspect you do, too - that's probably why you listed it first...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[ashjun]

Hi,
I would have imagined that having the timber piles might actually add problem to your new construction instead of "taking the problem" away by reducing the loads to your new foundations.
30 years old timber; well, I myself wouldn’t guarantee that the wood preservation done that long ago would be able to preserve for the next 30 to 50 years.
Those timber piles most likely have been designed for end bearing (that was geotechnical engineering 30 years ago); if you could check the depth of the bearing stratum around the building by drilling boreholes, this could give you an estimate of the length of the pile. Furthermore, if the boreholes are also drilled within the building area (perhaps after breaking down of the existing superstructure (?) ), the depth of timber piles could also be estimated by taking water content measurement of the soil with depth both near to the timber piles and in the area free from the influence of the piles. Water content upto the depth of the piles would "usually" be less and where the piles have terminated, the water content would "generally" be higher. Anyway this is real hot water to walk in without any other estimate.
My suggestion is however to treat this depth against decay of wood and to prevent volume changes of the soil during the decay.
Important (and as suggested above): You could perhaps forget about the old wooded piles talking the load

Regards