Aarddruk

Aarddruk, literally meaning “earth pressure” in Dutch, refers to the lateral pressure that soil exerts on adjacent structures such as retaining walls, basement walls, underground excavations, or other vertical faces. It is a central concept in geotechnical engineering and soil mechanics, encompassing different states of stress depending on how the soil and the structure interact. The main states are active, passive, and at-rest earth pressure. Active pressure occurs when the wall moves away from the soil, causing the soil to shear and exert a relatively small lateral force; passive pressure occurs when the soil is compressed against a restrained or moving wall, generating higher lateral forces; at-rest pressure represents the condition when the wall is prevented from moving and the soil pressure is intermediate between the active and passive cases.

The calculation of aarddruk relies on earth-pressure theories, notably Rankine and Coulomb, which provide coefficients of lateral pressure. These coefficients relate the horizontal earth force to the vertical effective stress in the soil. For dry, frictional soils, the active and passive coefficients depend on the soil’s internal friction angle and, for cohesive soils, may also involve cohesion. In practice, factors such as backfill density, wall geometry, wall friction, drainage, groundwater and pore-water pressure, and whether the wall is allowed to move influence the actual pressures.

Applications include the design of retaining structures, basement and tunnel walls, and temporary shoring systems. Engineers use aarddruk estimates to determine bending moments, shear forces, and required reinforcements or tiebacks, while incorporating safety factors and drainage provisions to manage pore-water pressures. The concept has a long history in soil mechanics, with foundational contributions from Coulomb and Rankine in the 18th and 19th centuries. See also soil mechanics, earth-pressure theory, and retaining walls.