Cohesionless soils

Definition

Cohesionless soils are granular soils, such as sand and gravel, that do not exhibit significant cohesive strength. These soils rely primarily on the interparticle friction for their stability, making them behave differently under dynamic loads, such as those from seismic activity. Understanding the properties of cohesionless soils is crucial for predicting their behavior during earthquakes and designing appropriate foundations and structures in seismic regions.

5 Must Know Facts For Your Next Test

1. Cohesionless soils have low shear strength when compared to cohesive soils, which can lead to significant settlement or failure under dynamic loads.
2. The angle of internal friction in cohesionless soils plays a critical role in determining their stability and performance during an earthquake.
3. In seismic zones, the presence of water in cohesionless soils can increase the risk of liquefaction, leading to catastrophic failures.
4. Cohesionless soils can experience rapid changes in effective stress during shaking, which makes understanding their dynamic properties essential for engineering design.
5. Soil compaction techniques are often employed to increase the density and shear strength of cohesionless soils to improve their performance in earthquake-prone areas.

Review Questions

• How do cohesionless soils differ from cohesive soils in terms of their behavior under dynamic loading?
  • Cohesionless soils differ from cohesive soils primarily in their lack of significant cohesive strength. While cohesive soils rely on both cohesion and friction to resist shear forces, cohesionless soils depend mainly on interparticle friction. This makes cohesionless soils more susceptible to instability under dynamic loading conditions, such as earthquakes, where they may exhibit rapid changes in effective stress and potential failure mechanisms.
• Discuss the implications of liquefaction in cohesionless soils during seismic events and its impact on engineering practices.
  • Liquefaction occurs when saturated cohesionless soils lose their strength and behave like a liquid during seismic shaking. This phenomenon can cause severe ground deformation and foundation failures, leading to substantial damage to structures. As a result, engineering practices must consider the risk of liquefaction when designing foundations and structures in seismic regions, often requiring soil assessments, mitigation strategies like soil densification, or alternative foundation designs to enhance stability.
• Evaluate how understanding the dynamic properties of cohesionless soils contributes to safer building practices in earthquake-prone areas.
  • Understanding the dynamic properties of cohesionless soils is essential for developing safe building practices in earthquake-prone areas. By analyzing factors such as shear strength, density, and liquefaction potential, engineers can create designs that account for the specific behavior of these soils under seismic loads. This knowledge allows for better prediction of ground response during earthquakes, enabling engineers to implement appropriate mitigation measures and design resilient structures that can withstand potential ground movement, ultimately reducing the risk of catastrophic failures.

Related terms

Granular soils: Soils composed of discrete particles, typically classified into sand and gravel, characterized by their ability to drain quickly and lack cohesive forces.

Shear strength: The resistance of soil to shearing forces, which in cohesionless soils is largely dependent on internal friction and density rather than cohesion.

Liquefaction: A phenomenon where saturated cohesionless soils lose strength and behave like a liquid during strong seismic shaking, posing a risk to structures.