What does a decrease in void fraction in soil indicate?

A decrease in void fraction in soil indicates consolidation of soil. The void fraction is the ratio of the volume of voids (spaces between soil particles) to the total volume of the soil sample. When consolidation occurs, typically due to an increase in effective stress, the volume of voids decreases as water is expelled from the pores between the soil particles. This expulsion leads to a more compact arrangement of the soil grains, which results in a lower void fraction.

Consolidation is a critical process in geotechnical engineering as it affects the strength, compressibility, and overall stability of soil. Understanding this relationship helps engineers evaluate how soil will behave under loads over time, particularly for structures and foundations.

Other choices reflect different soil behaviors that are not directly associated with a decrease in void fraction. For example, a loss of soil strength is typically not a direct result of decreased void ratio; rather, consolidation generally increases the strength of saturated soils as pore pressures decrease. Increased water retention would be indicated by a higher void fraction, as retaining more water means a greater volume of voids. Enhanced permeability would suggest that the soil is allowing water to flow through it more easily, which might occur with a higher void ratio, not a lower one.