Secondary compression

Definition

Secondary compression refers to the gradual deformation of soil that occurs after primary consolidation has taken place, typically due to the rearrangement of soil particles and the expulsion of pore water over time. This process is crucial in understanding how soils behave under long-term loading, especially in saturated soils where pore pressures play a significant role.

5 Must Know Facts For Your Next Test

1. Secondary compression can continue for years or even decades after the initial loading, making it important for long-term infrastructure planning.
2. It is particularly significant in soft clay soils, which can exhibit substantial secondary compression due to their unique properties.
3. The rate of secondary compression is influenced by factors like moisture content, loading history, and soil structure.
4. Understanding secondary compression helps engineers design foundations and other structures that remain stable over time.
5. Field tests, such as oedometer tests, are commonly used to measure secondary compression in soils and predict future behavior.

Review Questions

• How does secondary compression differ from primary consolidation in terms of soil behavior over time?
  • Secondary compression follows primary consolidation and represents additional volume reduction that occurs due to particle rearrangement and water drainage after the initial load is applied. While primary consolidation happens relatively quickly as pore water is expelled under load, secondary compression occurs slowly over a longer duration, reflecting ongoing changes within the soil structure. Understanding this distinction helps engineers evaluate the long-term stability of structures built on compressible soils.
• What factors influence the rate of secondary compression in saturated soils, and how can this impact engineering projects?
  • The rate of secondary compression in saturated soils is influenced by factors such as moisture content, loading conditions, and the inherent properties of the soil. For instance, softer clays may exhibit higher rates of secondary compression compared to denser soils. This is critical for engineering projects because if not accounted for, it can lead to unexpected settlement or instability over time, necessitating more robust design strategies to mitigate these effects.
• Evaluate the implications of secondary compression on the design and performance of civil engineering structures over their lifespan.
  • Secondary compression has significant implications for the design and performance of civil engineering structures, as it can lead to ongoing settlement issues long after construction is complete. Engineers must evaluate potential secondary compression when designing foundations, retaining walls, or other structures on compressible soils to ensure they remain stable under expected loads. Failure to adequately account for this phenomenon can result in structural damage or failure, impacting safety and functionality while increasing maintenance costs over time.

Related terms

primary consolidation: The initial compressive response of saturated soil due to the application of load, leading to a decrease in volume as pore water is expelled.

effective stress: The stress that contributes to soil strength and stability, calculated as total stress minus pore water pressure.

creep: The slow, continuous deformation of soil under constant load over time, often associated with secondary compression.