Piling and foundations Pile drivability tool
Pile drivability tool
Check whether an impact hammer can drive a pile to depth, and what each blow does to the pile, with a wave equation model you run from your browser.
Open the calculator Version 0.2.3
- Status
- Preview only, not public
- Method
- Smith (1960) wave equation, one-dimensional
- You enter
- Pile, hammer, cushion and soil resistance with quake and damping
- You get
- Blow count, set per blow, peak driving stresses against the limit, energy delivered, bearing graph
- Version
- 0.2.3
How it works
- The pile is split into short segments, each a mass joined to the next by a spring. Each segment has a soil element on its side and the toe has its own.
- Each soil element behaves elastically up to a small movement called the quake, then slips at its share of the soil resistance. A damping term adds resistance that grows with pile speed.
- The hammer is a ram that hits a cushion spring at the speed its drop and efficiency give. The model steps through time in very small increments and tracks the stress wave down the pile and back.
- One run gives the permanent set per blow and the peak compression and tension. Repeating the run at several resistance levels gives the bearing graph: blow count against soil resistance.
- Peak compression in a steel pile is checked against 0.9 times its minimum yield strength, the AASHTO driving stress limit reproduced by the FHWA.
Limits
- It does not replace a commercial wave equation program, a site investigation or dynamic and static load testing on the real piles.
- Quake and damping defaults are textbook starting values, not site measurements, and they control the answer.
- The cushion is a spring that only pushes, with an assumed stiffness. A stiffer cushion gives higher peak stresses, so use a value close to the real hammer's.
- The driveability profile against depth is derived from the bearing graph, not a separate run at every depth. Soil setup and relaxation are not modelled.
- The signal matching tab is an automated fit in the spirit of CAPWAP, not the commercial program, and has not been calibrated against load tests. Its demonstration records are synthetic.
- Each address can run one analysis a minute and 10 in any 24 hours, so the shared server stays responsive for everyone.
Worked example
Example only, not a real site. The tool opens with a one-click worked example. Every soil value is an invented round number chosen to show how the tool works.
| Pile | Open-ended steel pipe, 610 mm diameter, 12.7 mm wall, grade S355, 21 m long with 1 m above ground |
|---|---|
| Hammer | Junttan HHK 7A hydraulic impact hammer from the published catalogue data: 7,000 kg ram, 1.2 m stroke, 82 kJ rated |
| Efficiency and cushion | 80% hammer efficiency and a 500,000 kN/m cushion, both assumed |
| Soil | Soft clay to 5 m below ground, medium dense sand to 14 m, dense sand to the toe at 20 m |
| Resistance | About 1,040 kN along the shaft and 450 kN at the toe, about 1,490 kN in total |
| Quake and damping | 2.5 mm quake; damping 0.65 s/m in clay, 0.16 s/m in sand, 0.50 s/m at the toe |
| Blow count | About 11 blows per 250 mm (set about 23 mm per blow) | OK |
|---|---|---|
| Peak compression | 135 MPa, 42% of the 319.5 MPa limit for S355 | OK |
| Peak tension | 1.4 MPa. The cushion only pushes, so the rebound does not pull on the pile head | |
| Energy into the pile | 64.5 kJ, 79% of the 82 kJ rated |
An easy drive with stresses well inside the limit. In real work the soil values would come from the site investigation, and the prediction would be checked by dynamic testing during driving.
Open the tool
Open the calculator and press Run the worked example. The tool runs on the GeoMan ANZ server. Nothing you type into it is saved. To keep it available for everyone, it limits how often one address can run an analysis and keeps a short log of refused requests.
Version 0.2.3. The tool has its own page on method, limits and references. More on driven piles in the piling and foundations topic.
References
- Smith, E.A.L. (1960). Pile-driving analysis by the wave equation. Journal of the Soil Mechanics and Foundations Division, ASCE, 86(SM4), 35 to 61. doi.org
- Hannigan, P.J., Rausche, F., Likins, G.E., Robinson, B.R. and Becker, M.L. (2016). Design and Construction of Driven Pile Foundations, GEC No. 12, Vol. I (FHWA-NHI-16-009) and Vol. II (FHWA-NHI-16-010). Federal Highway Administration. www.fhwa.dot.gov
- Hannigan, P.J., Goble, G.G., Thendean, G., Likins, G.E. and Rausche, F. (1998). Design and Construction of Driven Pile Foundations, Vol. I (FHWA-HI-97-013). Federal Highway Administration. rosap.ntl.bts.gov
- Rausche, F., Goble, G.G. and Likins, G.E. (1985). Dynamic determination of pile capacity. Journal of Geotechnical Engineering, ASCE, 111(3), 367 to 383.
- Junttan HHK 7A datasheet, Junttan Oy. junttan.com