PDA Dynamic Load Testing for batter pile / CAPWAP

[hkp246]

Anyone familiar with pda please help me.

I am working on a project where HP 14 x 117 piles are driven vertically as well as battred (4:1 y/x slope). The piles normally penetrate and reach driving criteria at 100' to 105' reaching final blow count of 18-19 bpi. Bottom of piles are usually 50' and top segment of 65' spliced at 50 feet (total length of pile 115')

Can someone with experience or familiarity with PDA help me understand tension/compression slack. And perhaps some tips on how to represent the slacks in CAPWAP program.

Thank you

Hiral

 

[Panars]

How are your piles spliced? With a full penetration butt weld, there is no slack. The commercial splicers also use welds so there is no slack. Are you using a bolted splice plate?

 

[hkp246]

Panars, thank you very much for your response.

The Splices are full penetration butt weld. And yes you are correct about no slack. However, in some cases I have noticed that the efficiency of the splice deteriorates as pile is driven into the ground and possibly the splice fails. In this case how can slack be measured? What in your opinion causes the pile splice to fail? I believe that the uneven distribution of pile stress at the top might cause splice failure. For example if the hammer is not properly aligned with the pile then during driving the hammer might exert more stress on one side of the pile. Or maybe the hammer cushion?

Thank you for your previous response.

Hiral

 

[Panars]

You can model slack in CAPWAP as either distance-limited or force-limited. For a broken or partially broken splice, you would probably choose a force-limited slack. Using a minimal value of tension force (maybe 10 kN?) would be pretty close to a completely broken splice that transmits no tension. As to how you measure the slack - I don't know if you can. You would just try different force-limits and see what that does to your CAPWAP match quality.

As to what causes the splice failure, it is probably a problem with the weld. A proper full penetration butt weld should be stronger than the base metal. Can you perform any testing on the welds before driving? And yes, hammer misalignment would contribute to the problem because one side of the weld will have greater stress than the other, leading to a progressive failure. Are you using two strain gages, as recommended by PDI? If so, look at the individual readings to see how different they are. If they are very different, then you do have an issue with hammer misalignment.