Passive Pressure

Definition

Passive pressure is the lateral pressure exerted by soil or rock against a structure, such as a retaining wall, when the wall is displaced or moved away from the soil. This type of pressure increases as the wall moves and helps to stabilize structures by resisting lateral forces. Understanding passive pressure is crucial for designing retaining walls and ensuring their stability, especially during seismic events where ground movement can lead to increased forces on these structures.

5 Must Know Facts For Your Next Test

1. Passive pressure develops when a retaining wall moves away from the backfill soil, allowing soil particles to rearrange and exert increased lateral forces on the wall.
2. The magnitude of passive pressure depends on soil properties, including cohesion and friction angle, which are essential for accurate calculations.
3. In seismic conditions, passive pressure can significantly increase due to ground shaking, making it crucial to factor this into retaining wall designs.
4. Designing for passive pressure involves calculating the equilibrium state to ensure that structures can withstand not just static loads but also dynamic loads from seismic activity.
5. The Rankine-Wegman equation is often used to determine the passive pressure exerted on walls, incorporating variables like soil weight and wall height.

Review Questions

• How does passive pressure differ from active pressure in terms of soil behavior around retaining walls?
  • Passive pressure occurs when a retaining wall moves away from the soil, resulting in increased lateral forces exerted by the soil due to rearrangement of particles. In contrast, active pressure arises when the wall moves towards the soil, allowing it to expand and exert less force. Understanding these differences is vital for engineers to ensure proper design and stability of retaining structures under varying conditions.
• What role does the Earth Pressure Coefficient play in calculating passive pressure for retaining walls?
  • The Earth Pressure Coefficient is a critical parameter that helps determine the relationship between horizontal stress and vertical stress in soil. It is used to calculate both active and passive pressures acting on a retaining wall. By accurately assessing this coefficient based on soil conditions, engineers can estimate how much passive pressure will resist lateral movements during events like earthquakes or changes in soil moisture.
• Evaluate how seismic forces affect passive pressure and what considerations should be made in retaining wall design.
  • Seismic forces greatly influence passive pressure by increasing lateral loads on retaining walls during ground shaking. This means that engineers must design retaining walls with enhanced capacity to resist these additional forces. Key considerations include selecting appropriate materials, accounting for dynamic loading conditions in calculations, and possibly integrating flexible designs that can accommodate movement without compromising structural integrity.

Related terms

Active Pressure: Active pressure is the lateral earth pressure exerted on a structure when the wall moves towards the soil, allowing the soil to expand and exert a lesser force.

Earth Pressure Coefficient:

This coefficient represents the ratio of horizontal stress to vertical stress in soil and is key in calculating both active and passive pressures.

Seismic Forces: These are forces generated during an earthquake that can impact the stability of structures, making passive pressure even more critical in design considerations.