Foundations · Pile testing & NDT
Impulse response (mobility) test: length and impedance calculator
Length from the spacing of resonant peaks in the mobility spectrum, and the equivalent diameter from the measured characteristic mobility.
Standard: ASTM D5882 transient response · Δf = c/2L · N = 1/(ρcA)
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Wave speed c | 3900 | m/s |
| Concrete density ρ | 2400 | kg/m³ |
| Nominal diameter | 0.6 | m |
| Record length | 12 | m |
| Resonant peak spacing Δf | 162.5 | Hz |
| Measured mean mobility N | 0.39 | ×10⁻⁶ m/s/N |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Nominal area | 0.283 | m² |
| Theoretical mobility 1/(ρcA) | 0.378 | ×10⁻⁶ m/s/N |
| Equivalent diameter √(4/(πρcN)) | 0.591 | m |
| Check: De / D | 0.984 | |
| Check: |length deviation| | 0.000 | % |
| Length L = c/(2Δf) | 12.00 | m |
- ✓ Length within ±5 % of record
- ✓ Equivalent diameter ≥ 95 % of nominal
Method, formulas and assumptions
- Nominal area = PI()*0.6^2/4 = 0.28274 m²
- Theoretical mobility 1/(ρcA) = 1000000/(2400*3900*0.28274) = 0.37786 ×10⁻⁶ m/s/N
- Equivalent diameter √(4/(πρcN)) = SQRT(4/(PI()*2400*3900*0.39/1000000)) = 0.59059 m
- Check: De / D = 0.59059/0.6 = 0.98431
- Check: |length deviation| = ABS(3900/(2*162.5)/12-1)*100 = 0 %
- Length L = c/(2Δf) = 3900/(2*162.5) = 12 m
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.