Capacity of Old Timber Piles

[Mudcake]

Renovations of a c. 1926 Fire Station are planned. The building has a basement and is supported on timber piles with concrete pile caps. Groundwater is near the top of pile caps. The planned renovation will increase loads on the existing piles. Any non-destructive testing that can be used to estimate the capacity of the existing piles?

 

[jdonville]

Mudcake,

Well, the piles should be in a generally good condition, owing to the moisure in the soil. Unfortunately, other than back-calculating the design capacity from construction records using modern design relations, I can't think of much that could be done to test the "actual" capacity of the piles. You may wish to play it safe and specify additional elements to take the change in load. I would try to justify the re-use/continued use of the existing piles, if at all possible.

Try contacting the Timber Pile Council. Maybe they have some ideas.

Jeff

 

[VAD]

Static load testing could be a possibility depending on what is expected to be done in renovation etc etc

 

[BigH]

Be careful with timber piles. If you permit them to dry out, then rewet, you may have problems develop. Best not to expose them and subject them to drying/rewetting. I have seen pictures of timber piles in "very good condition" exposed for an 'inspection' and then backfilled. A couple of years later, the same pile was unearthed again to see the condition and it had gone to hell in a handbasket.

 

[civilperson]

Timber piles that can resist insertion of a nail by finger strength is good for 600 lb/square inch ultimate or 200 lbs/square inch usable loading. This is rule of thumb developed in Louisiana and seems to work. I do not know what value to use if the nail is pushed in with just one hand.

 

[DRC1]

We have tested timber piles under bridge piers. We constructed approach pits to the piles. We then cut out a section of a pile. We used high strength self leveling (which does not self level as easily as one would think)to create a cap on top of the pile. We the ran a static load test. The cut out section was replaced by a steel section after the test.
Although we did not have a problem here, Big H is right, if you are working with piles at or near the water table, be sure they don't dry out.

 

[GSI2722]

I have performed a soil boring alongside the timber pile to establish the subsurface profile. The Pile Integrity Test to estimate the length of pile. It is not always successful though to get adequate wave reflection.

Now that you have determined the soil profile and strength properties via SPT and/or strength testing on collected specimens, perform a statice analysis (I use Allpile by Civilsoft). Use an appropriate factor of safety.

Also, I have performed a static load test by jacking between an old timber pile and a pile cap.