Which pressure is exerted when a wall is allowed to move outward, like a typical retaining wall?

The pressure exerted when a wall, such as a typical retaining wall, is allowed to move outward is referred to as active pressure. This concept is pivotal in the analysis of earth retaining structures, where the soil exerts pressure on the wall.

Active pressure occurs when the wall moves away from the soil, allowing the soil particles to rearrange and exert less pressure on the wall compared to when the wall is stationary. This movement corresponds to the condition where the wall is effectively 'active', and allows the soil to expand and exert force less than what is present when the wall is stationary.

Understanding this concept is essential for engineers when designing retaining walls, as it influences how the wall is constructed and how it will behave under various conditions. The analysis of active pressure is primarily based on Rankine's theory or Coulomb's earth pressure theory, which provides formulas to calculate the magnitude of pressure exerted by soil on a retaining wall.

In contrast, at-rest pressure is the condition where the wall is stationary, and the soil exerts its maximum pressure on the wall without any movement. Passive pressure, on the other hand, refers to the pressure exerted by the soil when the wall moves inward, causing the soil to become denser and exert a