Cofferdam Seepage & Piping Check (Flow-Net Based)

Simple flow-net style model: seepage discharge, exit gradient, and factor of safety against piping for a cofferdam / sheet-pile cutoff. Optional uplift (base heave) check using a simplified pore pressure estimate.

Inputs

Units

Current units: SI — heads in m, k in m/s, γ in kN/m³, stresses in kPa.

Hydraulic heads (relative to excavation base)

Measure water levels vertically above the excavation base (z = 0 at base).

Upstream head H_up m

Inside head H_in m

Flow net parameters

Use N_f, N_d

Flow channels N_f

Potential drops N_d

Characteristic exit length L_exit m (approx. thickness of last element at toe)

Soil & safety parameters

Hydraulic conductivity k m/s

γ_sat (soil) kN/m³

γ_w (water) kN/m³

Critical gradient i_cr (optional) If blank, computed from γ_sat, γ_w

Uplift check (optional)

If you enter a soil thickness below the base, the tool will estimate FS against uplift at the base.

Soil thickness below base H_soil m

Summary

Enter heads, flow-net parameters (N_f, N_d), k and soil properties, then click Compute seepage & FS. This estimates seepage discharge, exit gradient and FS against piping, plus optional uplift FS at the base.

Profile, table & exports

Cofferdam seepage profile (flow-net model)

Drop index	Depth (approx.)	Head h	u = γ_w·h	i (between levels)
No profile yet.

Theory & references

Open formulas and sources

This tool follows standard flow-net relationships: seepage discharge from N_f, N_d and exit gradient at the downstream toe. Use this for preliminary design checks.

Total head loss Δh = H_up − H_in Seepage discharge per unit length q = k · Δh · (Nf / Nd) Average head drop per potential Δh_drop = Δh / Nd Approx. exit gradient at toe i_exit ≈ Δh_drop / L_exit Critical gradient (if not provided) i_cr ≈ (γ_sat − γ_w) / γ_w Factor of safety against piping FS_p = i_cr / i_exit

Optional uplift FS is a simplified check based on estimated base pore pressure and submerged unit weight.

References

Cedergren, H. R. (1989), Seepage, Drainage, and Flow Nets.
Das, B. M. (Foundation Engineering texts), seepage and piping chapter.
NAVFAC DM 7.2 (Foundations & Earth Structures): seepage, piping and uplift guidance.
USACE EM 1110-2-1901: Seepage Analysis and Control for Dams (flow-net + seepage control concepts).