Model earth and hydrostatic loads for temporary enclosures. Compare inside and outside water levels. Choose safety factors, then download tables and summaries easily onsite.
Enter site conditions. Use consistent units shown.
Sample inputs and typical outputs for quick checking.
| H (m) | q (kPa) | φ (deg) | γm (kN/m³) | γsat (kN/m³) | WT out (m) | Water in (m) | FS | Max design p (kPa) | Force (kN/m) |
|---|---|---|---|---|---|---|---|---|---|
| 6 | 10 | 30 | 18 | 20 | 0 | 0 | 1.0 | ~84 | ~250 |
| 5 | 5 | 34 | 17 | 20 | 1 | 2 | 1.2 | ~55 | ~140 |
| 8 | 15 | 28 | 19 | 21 | 0 | 3 | 1.1 | ~120 | ~520 |
Cofferdams rely on temporary walls to resist soil and water actions during excavation. This calculator estimates lateral pressure along the retained height and converts it into force and overturning moment for quick stability screening.
Enter retained height, surcharge, friction angle, cohesion, and unit weights. Typical moist unit weight is 17–19 kN/m³, saturated 19–21 kN/m³, and freshwater 9.81 kN/m³. Wall length b lets you report per meter or per panel.
The tool uses Rankine active conditions with Ka = tan²(45° − φ/2). For φ = 30°, Ka ≈ 0.333, producing a triangular soil component that grows with depth. Cohesion, if provided, reduces effective lateral stress but is limited to zero.
Below the outside water table, submerged unit weight γ′ = γsat − γw is applied to effective stress, while pore pressure u = γw(z − dwt) adds to total pressure. This separation helps reflect buoyancy yet keeps hydrostatic effects explicit.
Inside water level reduces net demand on the wall. If the excavation is partially flooded or intentionally balanced, the calculator subtracts inside hydrostatic pressure from the outside total, preventing overly conservative bracing estimates when water levels equalize.
Surcharge represents cranes, spoil, traffic, or stored materials. Common temporary surcharges range from 5 to 20 kPa; heavy equipment near the edge can exceed this. Because surcharge is applied to vertical stress, it increases lateral pressure uniformly with depth through Kaq.
The pressure profile is integrated numerically to obtain force F and base moment M. The centroid depth indicates where the resultant acts; deeper centroids raise moments and may require stronger wales, struts, or tiebacks, especially for tall cells.
Use FS to scale net pressure for design checks, then export CSV and PDF for calculations logs. Always confirm soil parameters from lab or in situ tests, consider seepage gradients, and compare results with project specifications and temporary works plans. For layered soils, run multiple cases using upper and lower bounds; for example, φ ± 3° and γ ± 1 kN/m³. For cohesive deposits, reduce reliance on c for long durations because cracking and construction vibrations can mobilize lower effective strength. Check timber or steel sheet limits against peak design pressure at depth.
FS multiplies the net lateral pressure profile to create a conservative design profile. It does not replace structural code checks; it simply scales pressures so you can compare bracing options and review sensitivity quickly.
Use project geotechnical values when available. If you need a quick range, sands often use φ 28–38° with γm 17–19 kN/m³, while silty sands may be slightly lower. Confirm with tests.
If cohesion is entered or inside water counterpressure is high, the computed net pressure may drop below zero. The calculator clips negative values to zero because tension cannot be carried by soil against the wall.
It assumes a single set of parameters over the retained height and evaluates active conditions only. For layers, run separate scenarios or use conservative averaged properties. Passive resistance and embedment design must be checked separately.
Light vehicles may be represented by 5–10 kPa, while heavy equipment or stockpiles can be 15–30 kPa or more, depending on distance from the edge. Use the most critical expected condition.
The calculator integrates the pressure distribution to get total force and base moment. The resultant location is the moment divided by force, reported as meters above the base and as depth below the top.
The CSV and PDF are helpful calculation records, but submittals typically require assumptions, drawings, and independent verification. Attach geotechnical references, water level notes, and checks for struts, wales, and sheets.
Use engineering judgment and verify against project requirements.
Safer cofferdams start with accurate pressure assumptions today.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.