Which type of consolidation occurs gradually in clayey soils due to water extrusion?

Primary consolidation occurs gradually in clayey soils as a result of the expulsion of water from the soil pores under sustained loading. When a load is applied to clay, the water within the soil structure begins to drain out, leading to a reduction in pore water pressure and a corresponding increase in effective stress. This process is driven by the slow dissipation of pore pressures, which can take considerable time due to the low permeability characteristics of clay soils.

During primary consolidation, the soil volume decreases as the water is forced out, and this process continues until the excess pore pressure has dissipated and the soil reaches a new equilibrium state. This consolidation phase is typically observed over days, months, or even years, depending on the clay's permeability and the load magnitude.

Understanding primary consolidation is crucial for predicting settlement in structures built on clayey soils, as it affects the long-term behavior and stability of the foundations. This process contrasts with immediate settling, which occurs instantaneously upon loading; secondary consolidation, which follows primary consolidation and is related to long-term adjustments in soil structure or fabric; and elastic deformation, which refers to the immediate, recoverable deformation that occurs under loading.