What specific soil parameter quantifies the rate at which primary consolidation settlement progresses in a saturated clay layer?

The specific soil parameter that quantifies the rate at which primary consolidation settlement progresses in a saturated clay layer is the coefficient of consolidation, denoted as Cv. Primary consolidation settlement is the time-dependent reduction in volume of a saturated clay layer caused by an applied load. This settlement occurs as excess pore water, initially carrying a portion of the applied load within the soil's interconnected voids, is slowly expelled from the clay. As the water is squeezed out, the load is progressively transferred from the pore water to the soil's solid particles, leading to an increase in effective stress within the soil skeleton and a corresponding decrease in the overall volume of the clay layer. The coefficient of consolidation (Cv) directly governs how quickly this process of pore water expulsion and effective stress transfer takes place, thereby quantifying the rate of settlement. A higher Cv indicates that the excess pore water pressure dissipates more rapidly, leading to a faster progression of primary consolidation settlement. Conversely, a lower Cv signifies a slower dissipation of pore water pressure and a more gradual settlement over a longer period. Cv is an intrinsic soil property that combines two fundamental aspects of the clay: its hydraulic conductivity and its compressibility. Hydraulic conductivity (often referred to as permeability) measures the ease with which water can flow through the soil's pores. A higher hydraulic conductivity allows pore water to escape more rapidly, contributing to a faster rate of consolidation. Compressibility describes the soil's tendency to reduce in volume under increasing effective stress. The coefficient of consolidation is directly proportional to the hydraulic conductivity and inversely proportional to the coefficient of volume compressibility and the unit weight of water, meaning that both the ease of water flow and the magnitude of volume change for a given stress increment contribute to how quickly the consolidation process unfolds.