Rule of Thumb for Mobilizing Full Capacity During PDA Testing?

[JHeisenberg]

I was told at pile penetration resistances over around 10BL/in. you are likely not fully mobilizing and your PDA is likely under predicting your capacity. Can anyone confirm or deny this? Does anyone know of any good sources of research on this topic?

 

[MTNClimber]

Not sure of the actual answer here but based my experience the PDA is usually conservative with H-piles driven to shale bedrock. I've had people tell me that the PDA is usually conservative in general.

I had a project with HP12s and HP14s driven 120+ feet down to shale. We PDA'd one of each and then performed a static load test.

The final blows for the HP14x89 were 10-8-11-12, PDA capacity at end of driving was around 680 kips, re-strike the next day was 700 kips, and the static load test was 920-1000 kips (based on Davisson's criterion).

The final blows of the HP12x74 were 6-10-9-9, PDA capacity at the end of driving was 585 kips, re-strike the next day was 575 kips, and the static load test was 612-640 kips.

We PDA'd several more piles on the project but didn't load test them. HP12x74 PDA results ranged from 540 to 640 kips. HP14x89 ranged from 675 to 820 kips.

 

[L0k]

Hi MTNClimber, I am interested to your experience in PDA & static loading test.
Can you inform us some information on the static load tested piles such as: the hammer weight, falling height, final set & rebound value?

 

[HENRYZAU]

JHeisenberg,

Yes certainly for closed-end driven piles, but different value may apply for open-ended driven steel tubular piles due to potential plugging and founding material (soil vs. rock).
References: FHWA-NHI-16-009, NCHRP SYNTHESIS 478, FHWA-AK-RD-12-07

 

[JHeisenberg]

That is interesting info MTNClimber, thanks.

I will look into those references HENRYZAU.

 

[MTNClimber]

L0k,

The hammer was a Junttan HHK-9A hydraulic hammer so there isn't a fall height. The rig provides an estimated energy level for each blow. But in case you were wondering the HHK-9A has a ram weight of 19.84 kips, max stroke of 4 feet, and a max rated energy of 79.36 ft-kips.

The hammer was running around 51 ft-kips for the HP14x89 and 44 ft-kips for the HP12x74 (based on the PDA test results). I've noticed that the estimated energy on the rig doesn't always match the PDA, especially if the pile driving contractor does not input the correct hammer specs into the computer.

For the static load tests, the piles failed around 1.5 to 2-inches of displacement. Pile set was around 0.4". Not sure what rebound is but I'm guessing it's displacement at failure minus pile set?

Also just, an FYI, the final blows were blows/inch.

 

[L0k]

Thanks, MTNClimber Based on your data I calculated the ultimate pile capacity are 640kips and 740kips for HP12x74 and HP14x89 respectively. I assumed the rebound value 0.6" and the hammer efficiency is 85%