Secondary consolidation

Definition

Secondary consolidation is the gradual increase in soil volume that occurs after primary consolidation has taken place, often due to rearrangement of soil particles and changes in pore water pressure. This process is important for understanding long-term settlement behavior in soils, as it can affect the stability and performance of structures built on or within these soils.

5 Must Know Facts For Your Next Test

1. Secondary consolidation usually occurs over a longer period compared to primary consolidation and can continue for years or even decades, depending on soil type and loading conditions.
2. The rate of secondary consolidation is typically much slower than that of primary consolidation, often leading to ongoing settlement issues that may not be immediately observable.
3. Factors influencing secondary consolidation include the moisture content of the soil, the type of soil, and external environmental conditions such as temperature and load variations.
4. In practice, engineers must consider both primary and secondary consolidation when designing foundations to ensure they can accommodate total expected settlement over time.
5. Secondary consolidation is particularly significant in clays, which tend to exhibit notable long-term settlement due to their plasticity and ability to rearrange under sustained loads.

Review Questions

• How does secondary consolidation differ from primary consolidation in terms of time scale and mechanisms involved?
  • Secondary consolidation differs significantly from primary consolidation in that it occurs after the initial volume change due to pore water expulsion. While primary consolidation is rapid and occurs within a relatively short time frame as pore pressures equalize, secondary consolidation is a slower process characterized by gradual rearrangement of soil particles and changes in pore water pressure. Understanding these differences is essential for predicting long-term settlement behavior in soils.
• What role does the oedometer test play in evaluating secondary consolidation properties of soils?
  • The oedometer test is crucial for assessing both primary and secondary consolidation characteristics of soils. By applying vertical loads and measuring the resulting deformations, this test helps determine the compressibility of soil layers. The results provide insights into how soils will behave under sustained loads, including predictions about the rate and magnitude of secondary consolidation, which informs foundation design and overall structural stability.
• Evaluate the potential impacts of neglecting secondary consolidation in foundation design, particularly in clayey soils.
  • Neglecting secondary consolidation in foundation design can lead to significant issues, especially in clayey soils known for their prolonged settlement characteristics. If engineers fail to account for long-term settlement caused by secondary consolidation, structures may experience unexpected differential settlement, leading to structural damage or failure. This oversight can result in costly repairs and safety hazards, emphasizing the need for comprehensive evaluations that include both primary and secondary settlement factors during the design process.

Related terms

primary consolidation: The initial process of volume reduction in saturated soil due to the expulsion of pore water under sustained loading.

oedometer test: A laboratory test used to measure the compressibility and consolidation characteristics of soil by applying vertical loads and observing the resulting deformations.

settlement: The downward movement of the ground surface resulting from the compression of underlying soil layers, which can affect buildings and other structures.