Wave Equation

[Gimbli]

Pile = 12" round
Pile lenght = 50 ft
Hammer = Linkbert - LB 520
Subsoil Conditions = 0 to 38 feet stiff clay average cohesion=1.5 ksf
38 to 50 feet = medium sands Nave = 25 bpf gwt = 15 to 20 ft

Static analyses predict = 260 kips
Load Test reached maximum counterweight load of 150 kips and as per load vx deflection curve it was far from failure. Maximum settlement was 0.178 in.

Driving Data shows 13 to 17 bpf during last 10 feet segment (40 to 50 feet deep)

My concern is that I could not make this scenario to be correlated with wave equation which says that with 25% gain/loss factor for friction, what I consider to low, a bpf count of about 16.5 should be expected. Whith gain/loss of .75 - which I feel more conformtable bpf count is 38 bpf.

Where is the missing link?

Would the calibration of the load cell be wrong? which I checked and is certified by a PE with recognized Lab.

Good news, design ultimate load is 100 kips

 

[vulcanhammer]

I'm not sure I understand the problem. Driving logs say 13-17 bpf during last 10 feet, wave equation analysis 16.5 bpf. Where is the discrepancy? Am I missing something?

With cohesive soils, one must always take into consideration the loosening of the soils during driving, and that the apparent resistance will be lower during driving than afterwards.

With friction, the "efficiency" usually quoted in wave equation literature refers to the mechanical efficiency of the hammer. The losses in the cushion, pile head, etc., are beyond that. So, if you assume 75% mechanical efficiency of the hammer, the percentage of enthru to the rated striking energy of the hammer will be lower.

The values "built into" wave equation programs are "standard" types of values. Diesel hammers do not see the efficiency variations of, say, air/steam hammers, because if they are not lubricated properly they simply cease to work.

More information on this subject is found at

http://www.vulcanhammer.net/wave/