Enter Shoring Design Parameters
This advanced tool estimates lateral pressure on temporary shoring from soil, surcharge, groundwater, and cohesion. It also calculates the resultant force, location of action, and support line load.
Worked Example
The table below shows a sample active pressure case for quick reference. This example uses a 6 m retained height, groundwater at 3 m, and a 12 kPa surcharge.
| Item | Sample Value | Unit |
|---|---|---|
| Pressure Condition | Active | — |
| Excavation / Shoring Height | 6.00 | m |
| Unit Weight Above Water | 18.00 | kN/m³ |
| Submerged Unit Weight | 10.00 | kN/m³ |
| Friction Angle | 30.00 | degrees |
| Cohesion | 0.00 | kPa |
| Uniform Surcharge | 12.00 | kPa |
| Water Table Depth | 3.00 | m |
| Earth Pressure Coefficient | 0.3333 | — |
| Total Base Pressure | 61.430 | kPa |
| Resultant Force per Meter Run | 164.145 | kN/m |
| Support Line Load | 410.363 | kN |
Calculation Method
Ka = (1 - sin φ) / (1 + sin φ)
K0 = 1 - sin φ
Kp = (1 + sin φ) / (1 - sin φ)
Above water table: σ'v = γz
Below water table: σ'v = γzw + γ'(z - zw)
Active / At-rest: ps = max(Kσ'v - 2c√K, 0)
Passive: ps = Kσ'v + 2c√K
pq = Kq
pw = γw(z - zw), for depths below the water table only
pt = ps + pq + pw
F = ∫ pt dz
y = [∫ pt(H - z) dz] / [∫ pt dz]
This calculator uses depth-based numerical integration to obtain the total force and its location above the base. For at-rest cohesive soils, the cohesion adjustment is a practical approximation and should be checked against your design basis.
Step-by-Step
- Select the pressure condition: active, at-rest, or passive.
- Enter excavation height, soil unit weights, friction angle, and cohesion.
- Add uniform surcharge if nearby loads influence the retained soil.
- Set the groundwater depth and water unit weight.
- Enter tributary support spacing to estimate load per support line.
- Choose the number of intervals for the graph and pressure table.
- Press the calculate button to display results above the form.
- Download CSV or PDF if you need to share or archive the output.
Frequently Asked Questions
1. What is shoring pressure?
Shoring pressure is the lateral load applied by retained soil, surcharge, and sometimes water against a temporary support system. It helps size sheeting, walers, struts, anchors, and other excavation support elements safely.
2. What is the difference between active and at-rest pressure?
Active pressure develops when the wall moves enough to mobilize lower lateral stress. At-rest pressure applies when movement is restrained. At-rest loads are usually higher and often govern stiff temporary support systems.
3. Why is groundwater included separately?
Groundwater creates hydrostatic pressure below the water table. Even if effective soil stress reduces underwater, water still pushes directly on the shoring face. Ignoring it can significantly underestimate total retained load.
4. Why can cohesion reduce active pressure?
Cohesion provides apparent shear strength, which can lower calculated active lateral pressure. However, short-term cohesion may degrade with time, weather, vibration, and saturation, so engineers often apply conservative adjustments.
5. When should I use submerged unit weight?
Use submerged or effective unit weight below the groundwater level whenever drained effective stress is appropriate. It represents the soil’s buoyant weight after water support is removed from the total stress.
6. What does resultant location mean?
The resultant location shows where the combined lateral force acts along the shoring height. It is important for support reactions, bending effects, and checking where the critical load application point occurs.
7. Can this calculator replace a professional design?
No. It is a practical calculation aid, not a substitute for geotechnical investigation, staged excavation review, code compliance, or detailed temporary works design by a qualified engineer.
8. What does tributary spacing change?
Tributary spacing converts force per meter run of wall into a line load for a support element. Larger spacing means each support member attracts more load from the retained ground.