Existing Timber Pile Capacity 1

[joemock]

Does anyone know if there is a simple method to go from SPT data to existing timber capacity? Is the ENR method acceptable if the area of the SPT is scaled to the pile's area?

Thanks

 

[joemock]

Clarification, the timber capacity is for 40' x 14" o.d piles, about 20 years old in brackish water.

Thanks.

 

[SlideRuleEra]

I doubt it. Timber pile capacity usually has a significant skin friction component. In some application, even the buoyancy of the wood is important.

http://www.SlideRuleEra.net

 

[BigH]

joemock - first, I presume the N values are "new" and you want to see if the timber piles would be satisfactory for either new construction atop or rehab or existing building. There is a great document of some 15 parts for Timber Piles that SlideRuleEra has on his website (take a bow, SRE); there is also a Timber Pile Design Manual you can download from the internet. Two important geometrics you need to either know or estimate is (1) the tip diameter and (2) hence the taper rate from the butt end to the tip. Using the N values, and Nordlund's equations can get you an idea of the capacity of the pile assuming from a geotechnical point of view. This is rather straightforward.
What is not necessarily straightforward is if there has been disintegration of the timber pile due to groundwater fluctuations, etc. If the piles were not treated, then there is likely a necking of the pile in the fluctuating zone. If the piles were "always" below water, I wouldn't worry about it (Sweden's Parliament building built some 900 years ago are on timber piles). This damage of the pile due to environmental attacks is the most important to evaluate - and the most difficult. You might say, "Ok, I'll open up a pile, draw down the water and inspect it." - Fine, but be prepared that the pile will go to hell in a handbasket in short order. I am aware of a project in Vancovuer where this happened. Even one wet/dry was detrimental.
Personally, if I knew that the pile was treated and not subjected to fluctuating water levels, I would use the computed value as per Nordlund taking into account to the permitted fibre stresses for the type of timber (pine, ash, hardwood, etc). For that size of pile in decent materials, 30 tons and even up to 40 wouldn't be unheard of as your pile size is rather large - most I dealt with were 12" at the butt and 7 to 8" at the tip.
- but do look at SRE's page and get the Timber Manual

 

[joemock]

BigH

Thanks for the info. Can you please check your links, the first one sends me to EBay and the second to Quest.

The timber piles are currently in use and supporting a concrete beam that a travel lift moves on. The owner wants to upgrade the travel lift. I have been asked to determine the allowable capacity of the finger pier structure.

No inspection has been done to the piles to my knoweldge. I think we would dive to inspect rather than draw down the water.

I calculated a Qf of about 35kips using Meyerhof and making some assumptions about the soil properties, so maybe I'm not too far off. I get about the same thing if I scale the area of the 2" SPT sample to the pile area.

Thanks again for your assistance.

 

[BigH]

Try

http://www.SlideRuleEra.net

The pile articles for timber are mainly from Louisiana practioners if I remember correctly but they used a lot of wood piles down in Neworlans!

For the Timber Pile Manual try:

http://www.timberpilingcouncil.org/manual/manual.html

Also see:

http://www.fpl.fs.fed.us/documnts/pdf1996/graha96a.pdf

See Tomlinson's Pile Design and Construction book (Viewpoint Press)

 

[joemock]

Thanks again BigH.