BeginnerTopic 38 of 112Civil & Structural
Earth pressure theories
Rankine and Coulomb methods compute lateral soil pressure.
In depth
Rankine: K_a=tan²(45°-φ/2) and K_p=tan²(45°+φ/2) for smooth vertical walls with horizontal backfill; Coulomb accounts for wall friction and slopes. At-rest K₀=1-sinφ. Active thrust P_a=½K_aγH². Surcharges, water and seismic load add pressure.
Key points
- Active needs small wall movement
- Passive resists
- Cohesive soils have tension cracks
ExampleFor φ=30°, K_a=1/3, so a 4 m wall in 18 kN/m³ soil sees 48 kN/m thrust.
What is Earth pressure theories?
Rankine and Coulomb methods compute lateral soil pressure.
Why is it important to understand earth pressure theories?
Earth pressure theories give the sideways force of soil on a wall, which is needed for every retaining structure.
What is active earth pressure?
The lower pressure that occurs when a wall moves away from the soil enough for the soil to reach failure, which is often used for design.
What is the Rankine theory?
A simple method that assumes a smooth wall and a uniform backfill, giving pressures from the friction angle of the soil.
How is Earth pressure theories used in practice?
Typical applications include calculating the active thrust on a wall that holds back sand, finding the earth pressure on a basement wall at rest and estimating the thrust from a clay backfill on a bridge abutment.
What should I learn before Earth pressure theories?
Study "Retaining walls" first (topic 37 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Earth pressure theories?
Active needs small wall movement. Passive resists. Cohesive soils have tension cracks.
Can you give an example of Earth pressure theories?
For φ=30°, K_a=1/3, so a 4 m wall in 18 kN/m³ soil sees 48 kN/m thrust.
What comes after Earth pressure theories?
The next topic is "Slope stability", which builds directly on this one.
How difficult is Earth pressure theories?
It is classed as Beginner in Civil & Structural (topic 38 of 112). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.