Cohesive soil

Definition

Cohesive soil is a type of soil that exhibits significant cohesion due to its fine-grained particles, such as clay and silt. These soils are characterized by their ability to stick together when wet, which affects their behavior under load and during ground improvement processes. The cohesive nature of these soils often influences construction techniques and the effectiveness of various ground improvement methods.

5 Must Know Facts For Your Next Test

1. Cohesive soils typically have a high water retention capacity, which can lead to challenges in construction due to potential swelling or shrinkage with moisture changes.
2. The engineering properties of cohesive soils, such as shear strength and compressibility, are greatly influenced by their moisture content and plasticity.
3. Cohesive soils can be improved using various ground improvement techniques, including compaction, grouting, and soil stabilization methods.
4. In cohesive soils, the presence of clay minerals significantly affects their behavior, with different types of clay exhibiting varying degrees of cohesion and plasticity.
5. Understanding the characteristics of cohesive soil is essential for predicting settlement behavior and designing effective foundations in geotechnical engineering.

Review Questions

• How do the properties of cohesive soil influence its behavior under load?
  • Cohesive soils exhibit significant cohesion due to their fine-grained particles, which leads to unique behaviors under load. When subjected to stress, cohesive soils tend to deform more plastically compared to granular soils. The shear strength of cohesive soils is influenced by factors such as moisture content and plasticity index, making them susceptible to changes in loading conditions. This understanding is crucial for predicting potential settlement and ensuring stability in construction projects.
• Discuss the importance of ground improvement techniques specifically for cohesive soils.
  • Ground improvement techniques are vital for enhancing the engineering properties of cohesive soils due to their inherent challenges, such as low shear strength and high compressibility. Techniques like compaction and chemical stabilization can increase the load-bearing capacity of these soils while minimizing risks associated with settlement or failure. Implementing appropriate ground improvement methods ensures that structures built on cohesive soils are safe and durable, addressing issues related to moisture fluctuations and soil instability.
• Evaluate the role of plasticity index in determining the suitability of cohesive soil for construction purposes.
  • The plasticity index is a critical factor in evaluating cohesive soil for construction since it indicates the range of moisture content within which the soil remains workable without losing its strength. A higher plasticity index suggests that the soil may experience significant volume changes with moisture fluctuations, potentially leading to instability in structures. By analyzing the plasticity index alongside other factors like shear strength and compressibility, engineers can assess whether a cohesive soil is suitable for supporting foundations or if ground improvement is necessary to ensure safety and performance.

Related terms

Plasticity Index: A measure of the plasticity of cohesive soils, calculated as the difference between the liquid limit and the plastic limit, indicating how much moisture a soil can retain before it loses its plasticity.

Shear Strength: The maximum resistance of a soil to shear stress, which is critical for understanding how cohesive soils behave under load and during construction activities.

Ground Improvement: Techniques used to enhance the physical properties of soil, especially cohesive soils, to improve their load-bearing capacity and stability for construction projects.