Non-cohesive soils

Definition

Non-cohesive soils are granular soils that primarily consist of particles that do not stick together, relying on friction and interlocking for stability. These types of soils include sands and gravels, which are characterized by their ability to drain water easily and exhibit high permeability. Non-cohesive soils play a significant role in various engineering applications, particularly when it comes to understanding their behavior under loading and during excavation.

5 Must Know Facts For Your Next Test

1. Non-cohesive soils have low plasticity and do not retain water well, making them prone to rapid drainage.
2. Due to their lack of cohesion, these soils are susceptible to changes in stress, which can significantly affect their stability during construction activities.
3. The angle of internal friction is crucial for predicting how non-cohesive soils will behave under load; typically, this angle ranges from 30 to 45 degrees.
4. Non-cohesive soils often require special consideration in design and construction projects, particularly in foundation engineering and slope stability analysis.
5. The behavior of non-cohesive soils can be modeled using Rankine's and Coulomb's theories for earth pressure, which help engineers calculate lateral pressures acting on retaining structures.

Review Questions

• How does the angle of internal friction influence the stability of non-cohesive soils in engineering applications?
  • The angle of internal friction is a key parameter in determining the shear strength of non-cohesive soils. A higher angle indicates greater resistance to sliding, which is crucial for ensuring stability in structures built on or within these soils. In engineering applications, understanding this angle helps engineers assess potential failure mechanisms and design foundations and retaining walls that can adequately support loads without failure.
• Discuss the implications of using Rankine's theory to analyze earth pressures in non-cohesive soils compared to cohesive soils.
  • Rankine's theory simplifies the calculation of lateral earth pressures by assuming that soil is isotropic and at rest. In non-cohesive soils, where friction is the primary source of strength, this theory can provide reliable estimates for active and passive earth pressures. However, it may not account for changes in moisture content or the effects of excavation on cohesive soils, which rely more heavily on cohesive forces. Therefore, while Rankine's theory works well for non-cohesive soils, engineers must remain cautious about its limitations when dealing with cohesive materials.
• Evaluate how understanding the characteristics of non-cohesive soils can impact construction projects involving foundations and slopes.
  • A comprehensive understanding of non-cohesive soil characteristics is vital for successful construction projects involving foundations and slopes. Non-cohesive soils tend to have high permeability and low shear strength when subjected to loading conditions, which can lead to instability or settlement issues. By evaluating properties like effective stress and the angle of internal friction, engineers can make informed decisions on design choices such as foundation depth, type of material used for backfill, and drainage solutions. This knowledge ultimately reduces the risk of failure and enhances the safety and longevity of constructed facilities.

Related terms

Granular Soil: Soils composed of larger particles, such as sand and gravel, that exhibit little or no cohesion and rely on friction for strength.

Effective Stress: The stress carried by the soil skeleton, defined as the total stress minus pore water pressure, critical in understanding soil behavior.

Angle of Internal Friction: A measure of the shear strength of non-cohesive soils, representing the maximum angle at which the soil can maintain stability against sliding.