Cohesion

Definition

Cohesion refers to the internal forces that bind together the particles within a soil mass, contributing to the soil's strength and stability. It plays a critical role in how soils behave under stress and influences their classification, particularly in distinguishing between cohesive and non-cohesive soils. Understanding cohesion is essential for predicting how soils will react to loading and environmental conditions.

5 Must Know Facts For Your Next Test

1. Cohesion is typically greater in clay soils compared to sandy soils, making clay more stable under load.
2. Cohesive soils can retain water better than non-cohesive soils, affecting their behavior in wet conditions.
3. The cohesive nature of soil is largely attributed to the presence of water and the electrochemical forces between particles.
4. In geotechnical engineering, cohesion is a key factor when designing foundations, slopes, and earthworks.
5. Cohesion contributes to the plasticity of soils, which affects their ability to be molded and shaped under pressure.

Review Questions

• How does cohesion influence the classification of soils and their engineering properties?
  • Cohesion is a fundamental characteristic that helps differentiate between cohesive soils, like clays, and non-cohesive soils, like sands. Cohesive soils exhibit significant internal bonding due to their particle size and water content, impacting their shear strength and stability. In engineering applications, understanding cohesion allows for better predictions of how different soil types will behave under various loads and conditions.
• Discuss the relationship between cohesion and shear strength in soil mechanics.
  • Cohesion directly affects shear strength, as it provides the resistance needed for soil particles to withstand shearing forces. The total shear strength of a soil can be expressed using the equation: $$ au = c + ext{(N)} imes an( heta)$$ where $$ au$$ is the shear strength, $$c$$ represents cohesion, $$N$$ is the normal force, and $$ heta$$ is the friction angle. This relationship is critical for evaluating soil stability in construction projects.
• Evaluate how variations in moisture content can impact the cohesion of different soil types.
  • Variations in moisture content significantly affect soil cohesion. In cohesive soils like clays, increased moisture can lead to reduced cohesion as water fills voids between particles and weakens their bond. Conversely, too little moisture can cause clay soils to dry out and lose plasticity, further affecting their cohesive properties. Non-cohesive soils like sands generally experience less impact from moisture variations since they rely more on friction than on cohesion for stability. Understanding these dynamics is vital for effective land use planning and construction.

Related terms

friction angle: The measure of the shear strength of a soil that is influenced by the internal friction between soil particles.

shear strength: The resistance of a soil to shear stress, which is determined by its cohesion and friction angle.

plasticity: The property of soil that allows it to deform under stress without cracking or breaking, often related to its moisture content and cohesion.