Example Data Table
| Case |
H (m) |
γ (kN/m³) |
φ |
q (kPa) |
Water depth (m) |
State |
| Dry retaining wall |
4.0 |
18.0 |
30° |
10 |
99 |
Active |
| Partly submerged wall |
5.0 |
19.0 |
32° |
15 |
2.0 |
Active |
| Rigid basement wall |
3.5 |
18.5 |
28° |
8 |
99 |
At-rest |
Formula Used
Rankine active: Ka = (1 - sin φ) / (1 + sin φ)
Rankine passive: Kp = (1 + sin φ) / (1 - sin φ)
At-rest: K0 = (1 - sin φ) × OCRsin φ
Effective vertical stress: σ′v = sum of effective soil weights above depth z
Lateral pressure: p = K(σ′v + q) ± 2c√K + u + kh(γz + q)
Resultant force: P = ∫ p dz
Base moment: M = ∫ p(H - z) dz
Lever arm: y = M / P
How to Use This Calculator
- Select active, passive, or at-rest pressure.
- Choose Rankine or Coulomb theory.
- Enter wall height, soil weight, and friction angle.
- Add cohesion only when reliable soil data supports it.
- Enter surcharge from traffic, slabs, or stored materials.
- Set water table depth from the retained soil surface.
- Add seismic coefficient when a simple comparison is needed.
- Enter wall weight and base width for screening checks.
- Press calculate and review the result above the form.
- Download the result table as CSV or PDF.
Understanding Lateral Soil Pressure
Lateral soil pressure is the force produced by retained earth. It acts on basements, quay walls, bridge abutments, and retaining walls. The force depends on soil weight, wall height, friction, surcharge, water, and movement. Small wall movements can change the pressure state. Active pressure occurs when a wall moves away from soil. Passive pressure occurs when soil is compressed. At-rest pressure is used when the wall cannot move enough.
Key Inputs
The most important input is retained height. Pressure normally grows with depth. Unit weight controls how fast it grows. Friction angle controls the earth pressure coefficient. Higher friction usually lowers active pressure and raises passive resistance. Cohesion can reduce active pressure near the top. It can also create a tension crack. Because cracks may fill with water, designers should use cohesion carefully. Surcharge adds a uniform lateral load. Traffic, slabs, equipment, and stored materials can create surcharge.
Water and Seismic Effects
Water table position is critical. Submerged soil has reduced effective weight. Yet pore water adds hydrostatic pressure directly. This means a wet backfill can push harder than dry soil. Drainage, filters, and weep holes reduce risk. The calculator separates effective soil pressure from water pressure. A horizontal seismic coefficient can add a simple pseudo-static pressure increment. It is not a substitute for full seismic design. It helps compare normal and earthquake loading.
Interpreting Results
The resultant force is reported per meter length of wall. The base moment is the overturning action about the wall toe. The lever arm shows where the resultant acts above the base. For a triangular pressure diagram, it is near one third of height. Uniform surcharge moves it upward. Water can also shift the resultant. Optional wall weight and base width estimate sliding, overturning, and bearing indicators. These checks are screening values only. Final design should follow local codes.
Good Design Practice
Use drained backfill when possible. Compact soil in controlled lifts. Avoid heavy surcharge near the wall crest. Check temporary construction stages. Review both service and extreme load cases. Compare active, at-rest, and waterlogged cases. Conservative inputs are safer when soil reports are limited. Confirm parameters with a geotechnical engineer before construction begins. Document assumptions with every saved calculation.
FAQs
What is lateral soil pressure?
It is the sideways pressure created by retained soil. It acts on retaining walls, basements, abutments, and buried structures. The value depends on depth, soil weight, friction, water, surcharge, and wall movement.
When should I use active pressure?
Use active pressure when the wall can move slightly away from the soil. This movement lets the soil relax. Many cantilever retaining walls are checked using active pressure.
When should I use at-rest pressure?
Use at-rest pressure when the wall is restrained. Basement walls, braced excavations, and rigid structures often need this case. It is usually higher than active pressure.
Does water increase lateral pressure?
Yes. Water reduces effective soil stress, but it adds hydrostatic pressure. Poor drainage can greatly increase wall load. Always check wet or blocked-drain conditions.
What does surcharge mean?
Surcharge is extra surface load behind the wall. It may come from traffic, foundations, stored materials, slabs, or equipment. The calculator converts it into a uniform lateral pressure.
Can cohesion reduce wall pressure?
Cohesion can reduce active pressure near the surface. However, it may be unreliable long term. Cracks, moisture changes, and construction disturbance can reduce cohesion benefits.
What does the seismic coefficient do?
The seismic coefficient adds a simple pseudo-static lateral increment. It helps compare normal and earthquake loading. It does not replace detailed seismic geotechnical design.
Are the stability checks final design values?
No. Sliding, overturning, and bearing results are screening checks. Final design should use project soil reports, drainage details, load factors, and local engineering codes.