Ground engineering · Groundwater & dewatering
Excavation base uplift & piping calculator
Uplift factor of safety of the clay plug over a confined aquifer and the exit-gradient piping check.
Standard: Hydraulic heave / exit gradient (Terzaghi)
Open the live calculator → All ground engineering calculators
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 |
|---|---|---|
| Thickness of impermeable plug below excavation | 6 | m |
| Plug saturated unit weight | 19 | kN/m³ |
| Piezometric head above aquifer top | 9 | m |
| Head loss across seepage path | 4 | m |
| Shortest seepage path at exit | 10 | m |
| Exit soil submerged γ′ | 9.5 | kN/m³ |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Uplift FS = γ D/(γw hw) | 1.29 | |
| Exit gradient Δh/L | 0.400 | |
| Critical gradient γ′/γw | 0.968 | |
| Piping FS ic/i | 2.42 |
- ✓ Uplift FS ≥ 1.2
- ✓ Piping FS ≥ 2
Method, formulas and assumptions
- Uplift FS = γ D/(γw hw) = 19*6/(9.81*9) = 1.2912
- Exit gradient Δh/L = 4/10 = 0.4
- Critical gradient γ′/γw = 9.5/9.81 = 0.9684
- Piping FS ic/i = 0.9684/0.4 = 2.421
Related ground engineering calculators
- Basement uplift, buoyancy and base-slab design — Basement below the design high groundwater level: hydrostatic uplift against the permanent dead load…
- Dewatering: drawdown, pumping rate and neighbour settlement — Excavation treated as an equivalent large-diameter well in an unconfined or confined aquifer: radius of…
- Well pumping: unconfined (Dupuit) & radius of influence — Discharge from a fully penetrating well in an unconfined aquifer with Sichardt's radius of influence.
- Confined aquifer drawdown (Thiem & Cooper–Jacob) — Drawdown at a distance and time using Cooper–Jacob, and steady Thiem discharge for comparison.
- Packer permeability test (Lugeon) — Lugeon value of each stage using the effective pressure at the test section (gauge + water column −…
- Pumping test analysis (Cooper–Jacob straight line) — Fits a straight line to late-time drawdown against log time in an observation well to give transmissivity…
- Slug test (Hvorslev) — Fits ln(H/H0) against time to find the basic time lag T0 and the hydraulic conductivity of the screened zone.
For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.