When does secondary consolidation occur in clayey soils?

Secondary consolidation in clayey soils occurs after primary consolidation has completed. This process happens over a longer duration, often driven by ongoing soil rearrangements and the dissipation of excess pore water pressure that was not accounted for during primary consolidation.

During primary consolidation, clay undergoes a rapid change in volume as water is expelled from its pores due to applied loads, leading to immediate settlement. This stage is characterized by a reduction in pore pressures and an increase in effective stresses.

Once primary consolidation is completed, the soil may experience secondary consolidation, also known as creep, where the volume change continues at a much slower rate due to factors such as long-term settlement, continued water drainage, or changes in moisture conditions. Essentially, it is the gradual adjustment of the soil structure to reach a new equilibrium after the primary compression has stabilized.

This understanding is critical for geotechnical engineering practices, particularly when designing structures on clayey soils, as it informs predictions of long-term settlement and the necessary considerations to ensure stability and integrity of the constructed facilities.