Site investigation · Geophysics & monitoring
Downhole seismic: interval Vs, Vs30 and site class calculator
Corrects slant travel times to vertical, computes interval shear-wave velocities, Vs30 and the site period of the soil above material with Vs ≥ 360 m/s, and suggests the AS 1170.4 site class.
Standard: ASTM D7400 · Vs30 · AS 1170.4 site period T = 4Σh/Vs
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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 |
|---|---|---|
| Source offset from borehole | 2.5 | m |
| Readings: depth (m), slant arrival time (ms) | 1, 16.83 2, 20.01 3, 24.41 4, 29.48 5, 34.94 6, 37.72 7, 40.77 8, 43.97 9, 47.26 10, 50.62 11, 54.02 12, 57.46 13, 60.92 14, 64.40 15, 66.22 16, 68.05 17, 69.91 18, 71.77 19, 73.64 20, 75.51 21, 77.40 22, 79.28 23, 81.18 24, 83.07 25, 84.97 26, 86.87 27, 88.77 28, 90.68 29, 92.58 30, 94.49 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Deepest reading | 30.00 | m |
| Site period 4Σh/Vs (Vs < 360) | 0.254 | s |
| AS 1170.4 class (indicative) | Ce | |
| Vs30 = 30/Σ(h/Vs) | 318.6 | m/s |
- ✓ Readings reach 30 m
Method, formulas and assumptions
- Deepest reading = MAX([t.z]) = 30 m
- Site period 4Σh/Vs (Vs < 360) = 4*SUM([t.ss]) = 0.25359 s
- AS 1170.4 class (indicative) = IF(0.25359>0.6,"De",IF(0.25359>0,"Ce","Be")) = Ce
- Vs30 = 30/Σ(h/Vs) = SUM([t.h30])/SUM([t.tt]) = 318.59 m/s
- Class Ee applies where more than 10 m of very soft soil (Vs ≤ 150 m/s, cu < 12.5 kPa or N < 6) is present; check the profile. Interval velocities are sensitive to timing errors where intervals are short.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.