PDA test

[drago8]

Hello all,

I would like to know your opinion on the subject. There is this one project of ours. The contractor has divided the piling works into phases, let's say: 4 phases. Consultant proposing to have 4 nos of PDA tests; in which 1 No for each phase.

Now, the client do not want to delay the work for PDA tests so they want to carry out all the PDA tests in this phase 1 of piling works. However by doing this, we would not know the results for the other phases. For info, the soil condition at that area is quite bad.

1) would you follow the client's request?
2) how long shall we wait after piling then can carry out PDA test?
3) why do we need to do PDA tests if we already done the load test?

Appreciate your opinion,



#LoveWins

 

[SlideRuleEra]

drago8 - You need a simple answer for a complicated question. There are a lot of factors to influence a decision. Some are as follows:

Details of bad soil. For example, does this mean friction piling... or is bad soil above a good layer that allows point bearing piling?

The Contractor's abilities and experience with pile driving at other projects near this site. Also, the specifications of the Contractor's pile driving equipment.

Type pile... concrete, steel, wood?

Pile plan layout. Also how the four phases are arranged. An example, if the piles are in groups, group action is more important than individual pile performance.

IMHO, if the load test was successful, I would perform one PDA test and provide a (money) credit to the Owner for not performing the other three PDA tests. If the load test and the PDA test do not agree, would tend to go with the load test results. The original purpose of PDA testing was to see if a pile can be driven successfully to design depth, NOT to second-guess the results of a load test.

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[jasonpc]

It depends on a few factors I think.

How many piles are to be driven in total, all phases? Are these 4 representative of 2% of production piles? How many borings were taken and how consistent is the soil strata?

Assuming lrfd was used, what resistance factor was selected to determine the pile lengths? This might be why a load test and PDA were required. There are different resistance factors depending on the regiment of testing done. A pile load test + PDAs on 2% production piles would result in the shortest pile lengths because of the level of certainty of this testing regiment. Driving performance can also be monitored on the fly by an inspector and compared to WEAP analysis or FHWA Gates Equation as a confirmation of performance compared to the PDA. Though this may not be as effective for friction piles depending on the soil. But I have found it to be very consistent with PDA tests in my own experience.

 

[drago8]

SlideRuleEra:

So the results from load tests are ultimate and the PDA tests are only carried out to justify Engineer's design. Is that correct?

jasonpc:

2% of production piles? Which code do you get this? So there is a clause to say how many PDA we are recommended to carry out for a certain area of site or total of piles in the project?

#LoveWins

 

[SlideRuleEra]

...results from load tests are ultimate...
...PDA tests are only carried out to justify Engineer's design.

Load test results may:
1. Be ultimate... or
2. Reveal that ultimate is greater than twice the design pile capacity.

PDA tests will:
1. Give an idea of pile load capacity.
2. Indicate stress in the pile during driving and if the pile has been damaged during driving.
3. Determine the energy delivered from the hammer to the pile.

How the Engineer uses that data depends on the details, as mentioned in my first post.

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[Okiryu]

If this is a design-build project, tell the client that without PDA, the design will be more conservative and therefore the factors of safety for pile design will increase, so he/she will need more piles... after hear this, they will may allow for the PDA tests...