Ground engineering · Groundwater & dewatering
Slug test (Hvorslev) calculator
Fits ln(H/H0) against time to find the basic time lag T0 and the hydraulic conductivity of the screened zone.
Standard: Hvorslev (1951): K = rc²·ln(Le/R)/(2·Le·T0), Le/R > 8
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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 |
|---|---|---|
| Casing radius rc | 25 | mm |
| Screen / filter pack radius R | 50 | mm |
| Screen length Le | 3 | m |
| Initial displacement H0 | 0.5 | m |
| Readings: time (s), displacement H (m) | 0, 0.5043 30, 0.4039 60, 0.3211 90, 0.2549 120, 0.2035 150, 0.1637 180, 0.1321 210, 0.1062 240, 0.0849 270, 0.0675 300, 0.0538 330, 0.0430 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Slope of ln(H/H0) vs t | -0.007 | 1/s |
| Basic time lag T0 = −1/slope | 134.5 | s |
| Fit R² | 1.000 | |
| K = rc² ln(Le/R)/(2 Le T0) | 0.000 | m/s |
| Check: Le / R | 60.00 |
- ✓ Le/R > 8 (shape factor valid)
- ✓ Fit R² ≥ 0.95
Method, formulas and assumptions
- Slope of ln(H/H0) vs t = SLOPE([t.ln],[t.tt]) = -0.0074364 1/s
- Basic time lag T0 = −1/slope = -1/-0.0074364 = 134.47 s
- Fit R² = RSQ([t.ln],[t.tt]) = 0.99994
- K = rc² ln(Le/R)/(2 Le T0) = (25/1000)^2*LN(3/(50/1000))/(2*3*134.47) = 3.172e-6 m/s
- Check: Le / R = 3/(50/1000) = 60
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.