What type of lateral earth pressure is exerted by a soil against a completely rigid retaining wall that does not move at all?

The type of lateral earth pressure exerted by a soil against a completely rigid retaining wall that does not move at all is known as at-rest earth pressure. Lateral earth pressure refers to the horizontal pressure exerted by soil on a vertical or inclined structure, such as a retaining wall. This pressure arises from the weight and internal characteristics of the soil. At-rest earth pressure specifically occurs when the retaining structure, and therefore the soil mass adjacent to it, experiences absolutely no lateral deformation or movement. This means the soil is in a state where there has been no strain in the horizontal direction. Since there is no movement, the soil mass is neither allowed to expand laterally away from the wall (which would lead to active pressure) nor compressed laterally towards the wall (which would lead to passive pressure). The internal stresses within the soil remain in equilibrium in its natural, undisturbed state before any lateral movement occurs. This condition is crucial because even a very small amount of wall movement can significantly change the pressure state. The magnitude of at-rest earth pressure is quantified by the coefficient of at-rest earth pressure, denoted as K₀. This coefficient is defined as the ratio of the horizontal effective stress (σ'h) to the vertical effective stress (σ'v) within the soil. Effective stress is the stress carried by the soil particles themselves, excluding the pressure of the pore water within the soil voids. For normally consolidated soils, which have never experienced a greater vertical effective stress in their history, K₀ can be approximated by Jaky's equation, K₀ = 1 - sin(φ'), where φ' is the effective angle of internal friction of the soil, representing its resistance to shearing. For overconsolidated soils, which have been subjected to higher vertical effective stresses in the past, K₀ values are generally higher than for normally consolidated soils and are also influenced by the overconsolidation ratio. At-rest pressure represents an intermediate state, being greater than active earth pressure (which occurs with outward wall movement) but less than passive earth pressure (which occurs with inward wall movement). It is a fundamental pressure condition used in the design of rigid retaining structures like basement walls, bridge abutments, or culverts that are not expected to deform.