Rankine Active Earth Pressure Coefficient

Definition

The Rankine Active Earth Pressure Coefficient is a measure used in soil mechanics to determine the lateral pressure exerted by soil on a retaining structure when the soil is allowed to expand. This coefficient is crucial for engineers to calculate the forces acting on walls and foundations, influencing the design and stability of structures. Understanding this concept helps in predicting how soil behaves under various conditions, which is essential for safe and effective civil engineering practices.

5 Must Know Facts For Your Next Test

1. The Rankine Active Earth Pressure Coefficient, often denoted as K_a, can be calculated using the formula: K_a = tan^2(45° - φ/2), where φ is the angle of internal friction of the soil.
2. This coefficient assumes that the backfill is horizontal and that there are no wall friction or surcharge loads acting on the wall.
3. In Rankine's theory, it is assumed that the soil is homogeneous and isotropic, meaning its properties are uniform in all directions.
4. The Rankine Active Earth Pressure Coefficient provides a simplified approach for engineers to estimate earth pressures without complex calculations.
5. Understanding this coefficient is essential for designing retaining walls, ensuring they can withstand lateral pressures without failing.

Review Questions

• How does the Rankine Active Earth Pressure Coefficient influence the design of retaining walls?
  • The Rankine Active Earth Pressure Coefficient directly impacts how engineers calculate the lateral forces acting on retaining walls. By understanding K_a, engineers can estimate the amount of pressure exerted by the soil behind the wall when it is allowed to expand. This helps in determining wall thickness, material choices, and reinforcement requirements to ensure stability and prevent failure under active earth pressures.
• Compare and contrast active and passive earth pressure coefficients and their relevance in civil engineering applications.
  • Active earth pressure coefficients, such as the Rankine coefficient, deal with conditions where the soil is allowed to move or expand, resulting in lower lateral pressures on structures. In contrast, passive earth pressure coefficients are relevant when soils are compressed against a structure, increasing lateral pressures. Both coefficients are critical for understanding how different loading conditions affect retaining structures, and engineers use them to optimize designs based on anticipated soil behavior.
• Evaluate how cohesion within soil layers can affect the Rankine Active Earth Pressure Coefficient and overall stability of structures.
  • Cohesion plays a significant role in influencing the Rankine Active Earth Pressure Coefficient because it alters how soil particles interact with one another. In cohesive soils, there may be additional forces at play that affect lateral pressure calculations compared to granular soils. Engineers must consider these effects when applying Rankine's theory, as ignoring cohesion could lead to unsafe designs that do not accurately represent real-world conditions. Understanding this relationship allows for better prediction of earth pressures and enhances overall structural stability.

Related terms

Active Earth Pressure: The horizontal pressure exerted by soil on a structure when the soil is allowed to move or deform, typically reducing pressure against the structure.

Passive Earth Pressure: The horizontal pressure exerted by soil when it is compressed or pushed against a structure, resulting in increased pressure on the structure.

Cohesion: The property of soil that allows particles to stick together, which affects the calculation of earth pressures and stability of structures.