Pile Driving Hammer Energy and Bearing Capacity
The Engineering News formula solved for the driving criterion a crew works to and the capacity at refusal...
Example
You enter
- Rated hammer energy (ft-lb) 42000
- Loss constant c (in) 0.1
- Required allowable capacity (tons) 150
- Specification refusal (blows per inch) 10
- Looser set to compare (in) 0.3
- Formula's embedded factor of safety 6
You get
- Set per blow required 0.180 in per blow
- Driving criterion 5.6 blows per inch, 67 per foot
- Blows per foot 66.6667
- Implied ultimate capacity 900 tons at the embedded factor of safety
- Capacity at refusal 210
- Refusal capacity ratio 1.4
- Capacity at the looser set 105 tons -- 30% below the requirement
- What the set measurement is worth 2
Checked against published worked examples from: California Department of Transportation (Caltrans).
Details, formula, and sources
ScopeThe Engineering News formula solved for the driving criterion a crew works to and the capacity at refusal and at a looser set. The worked hammer gives 5.6 blows per inch, and the 0.3 to 0.1 in set range spans a factor of two in capacity. A field control on a calibrated criterion, not a design method.
Formula or tableEngineering News R_allowable = 2 E / (s + c), with E in ft-lb, s the set per blow in inches, and c 0.1 in for steam, air, and diesel hammers or 1.0 in for a drop hammer; set = 2 E / R - c; blows per foot = 12 / s.
Source and editionThe Engineering News formula, carrying an embedded factor of safety of about 6 and returning an allowable rather than an ultimate load. The project specification, a wave equation analysis, and the geotechnical engineer govern.
Free accessA public historical relation.
What governsEstimate. AHJ and licensed professional govern.
API field nameshammer_energy_ftlb, loss_constant_in, required_capacity_tons, refusal_blows_per_inch, loose_set_in, embedded_safety_factor, set_in, blows_per_inch, blows_per_foot, ultimate_capacity_tons, refusal_capacity_tons, refusal_capacity_ratio, loose_set_capacity_tons, set_range_capacity_ratio
- What is missing nothing about the pile's length, stiffness, or mass, nothing about the cushion, and nothing about soil behaviour under a millisecond blowspec-v1832 caveat
- Refusal exists to protect the PILE, not to prove capacity; a pile at refusal in a soft layer above a hard one has proven nothingproject specification