| Scenario | Method | H (m) | γ (kN/m³) | φ′ (deg) | c (kPa) | q (kPa) | zw (m) | Typical outputs |
|---|---|---|---|---|---|---|---|---|
| Dry sand trench | Rankine Active | 4 | 18 | 32 | 0 | 5 | — | Max pressure and resultant force for sheeting checks. |
| Braced cut in sand | Apparent (Sand) | 8 | 19 | 30 | 0 | 10 | 6 | Uniform apparent pressure plus water pressure below zw. |
| Soft clay excavation | Apparent (Soft–Medium Clay) | 6 | 17 | 0 | 25 | 0 | 2 | Uniform apparent pressure using γH−4c lower-bounded. |
Shoring pressure in practical terms
Shoring pressure is the lateral load that soil and water apply to trench sheeting, soldier piles, or diaphragm walls. The calculator estimates this pressure as a function of depth and then integrates the profile to produce a resultant force (kN/m) and a moment about the base (kN·m per m).
Choosing the right earth pressure model
If the wall can move enough to mobilize active conditions, Rankine active is a common starting point. When movements are restrained (stiff walls, tight bracing, adjacent structures), at-rest pressures can be more realistic. For braced excavations, apparent pressure envelopes provide a convenient load shape for preliminary strut and wale sizing.
Input data ranges that make sense on site
Typical moist unit weight is often 16–22 kN/m³, while saturated unit weight may be 18–24 kN/m³. Drained friction angle for sands is frequently 28–38°, with lower values for silty sands and higher values for dense, clean sands. Surface surcharge may range from 5–20 kPa for traffic and storage, but higher values can occur near heavy equipment.
Groundwater and effective stress effects
When groundwater is present, the calculator uses submerged unit weight (γ′ = γsat − 9.81) below the water table and adds hydrostatic water pressure separately. This is critical because even if effective soil pressure reduces, water pressure can dominate at depth and significantly increase maximum total lateral pressure.
Interpreting results for bracing layouts
The resultant location above the base is useful for preliminary brace reactions. A lower centroid indicates higher loads near the bottom, often influenced by groundwater. Use the selected-depth profile table to sanity-check pressures at 25%, 50%, and 75% of H. For early sizing, the optional average strut load estimate distributes the resultant by strut levels and horizontal spacing. Always compare outputs with local codes and excavation methods.
1) Are the results per meter length of wall?
Yes. Pressures are in kPa, and the integrated force is kN per meter of wall length.
2) When should I use at-rest instead of active?
Use at-rest when wall movement is highly restricted by stiffness, tight bracing, or adjacent sensitive structures that cannot tolerate deformation.
3) Why can total pressure increase even with submerged unit weight?
Below the water table, effective soil stress may reduce, but hydrostatic water pressure grows linearly with depth and can dominate the total.
4) What does “resultant location above base” mean?
It is the vertical distance from the excavation base to the line of action of the total lateral force.
5) How is surcharge handled?
Surcharge is applied as an additional lateral component (K·q) for the chosen K, and added directly for the clay apparent options.
6) Can I use cohesion with any method?
This file applies cohesion adjustment only to Rankine active as a common simplification. For undrained clay design, use the clay apparent methods and confirm parameters.
7) Is the strut/anchor load estimate a design value?
No. It is a rough, average distribution for early checks. Final brace loads require a full support system analysis and construction-sequence assumptions.
- Rankine active coefficient: Ka = tan²(45° − φ′/2)
- Jaky at-rest coefficient (approx.): K0 = 1 − sin(φ′)
- Effective vertical stress: Above water table σ′v=γz, below water table σ′v=γzw + (γsat−γw)(z−zw).
- Effective lateral stress (general): σ′h = K·σ′v + K·q. For Rankine active with cohesion (optional): σ′h − 2c√Ka, with no tension allowed.
- Hydrostatic water pressure: u = γw(z − zw) for z > zw. Total pressure σh = σ′h + u.
- Apparent earth pressures (Peck 1969, simplified): sand: pa = 0.65 Ka γ′ H (uniform), soft–medium clay: pa ≈ max(γH − 4c, 0.3γH), stiff fissured clay: max ordinate about 0.2γH–0.4γH. Water and surcharge are added explicitly.
- Choose a design method that matches your support system behavior.
- Enter excavation depth, soil parameters, and any surface surcharge.
- If groundwater can act on the wall, enable it and set zw.
- Press Calculate to view pressures and resultants.
- Download a CSV or PDF report for documenting assumptions.