Earth pressure theories

Definition

Earth pressure theories describe how soil exerts pressure on structures such as retaining walls, foundations, and underground constructions due to the weight of the soil above. These theories are crucial for understanding the behavior of soil and its interaction with structures, allowing engineers to design safe and efficient systems that can withstand these pressures.

5 Must Know Facts For Your Next Test

1. Earth pressure theories are primarily based on two classic approaches: Rankine's theory and Coulomb's theory, which provide equations to calculate active and passive pressures.
2. The lateral earth pressure coefficient (K) is a key factor in these theories, representing the ratio of horizontal stress to vertical stress in the soil.
3. Soil properties such as cohesion, friction angle, and density significantly influence earth pressures and must be taken into account during design.
4. Earth pressure theories apply not only to retaining walls but also to other structures like deep foundations and excavation sites, making them vital in geotechnical engineering.
5. Changes in water level or soil saturation can dramatically alter earth pressures; thus, hydrostatic pressure is an essential consideration in designs involving groundwater.

Review Questions

• How do the concepts of active and passive earth pressures differ, and why is it important to understand both when designing retaining structures?
  • Active earth pressure occurs when a retaining wall moves away from the soil, leading to a reduction in lateral pressure on the wall. Conversely, passive earth pressure happens when the wall moves towards the soil, increasing the pressure. Understanding both concepts is crucial for engineers as it helps determine the maximum and minimum pressures that structures will experience during movement or settling, ensuring safe and effective designs.
• Discuss how Rankine's theory is used to calculate lateral earth pressures and its limitations in certain scenarios.
  • Rankine's theory simplifies the calculation of lateral earth pressures by assuming that the backfill is level and that there is no friction between the wall and soil. It provides straightforward equations for calculating active and passive pressures. However, this theory has limitations in cases with sloping backfills, non-uniform wall heights, or walls subjected to surcharge loads. In these situations, more complex models like Coulomb’s theory may be more appropriate.
• Evaluate how changes in groundwater levels impact earth pressure calculations and the design of structures such as retaining walls.
  • Changes in groundwater levels can significantly influence earth pressure calculations because they introduce additional hydrostatic pressures acting on retaining walls. When water levels rise, it increases lateral pressure on the wall due to buoyancy effects and additional weight from saturated soils. Engineers must evaluate these conditions thoroughly to ensure that designs can withstand fluctuating water levels while maintaining stability and preventing failures like sliding or overturning.

Related terms

Active Earth Pressure: The horizontal pressure exerted by the soil when a retaining structure moves away from the soil, causing the soil to expand.

Passive Earth Pressure: The horizontal pressure exerted by the soil when a retaining structure moves toward the soil, causing the soil to compress.

At-Rest Earth Pressure: The horizontal pressure exerted by the soil when a retaining structure is stationary and no movement occurs.