Cohesion

Definition

Cohesion is the property of soil that describes the attraction between soil particles, which contributes to the soil's strength and stability. This internal binding force is essential in understanding how soil behaves under different conditions, including how it interacts with moisture, external loads, and other forces acting on it.

5 Must Know Facts For Your Next Test

1. Cohesion plays a critical role in determining the shear strength of saturated and unsaturated soils.
2. In cohesive soils, like clay, cohesion can significantly enhance stability and resistance to shear failure.
3. The Mohr-Coulomb failure criterion incorporates cohesion as a fundamental component in predicting when soil will fail under stress.
4. Changes in moisture content can affect the cohesion of soil, making it vital to consider drainage conditions when assessing shear strength.
5. Cohesion is a key factor in the stability analysis of slopes and retaining walls, impacting their design and safety.

Review Questions

• How does cohesion affect the shear strength of different types of soil under varying moisture conditions?
  • Cohesion significantly impacts shear strength in cohesive soils like clay, where the attraction between particles enhances stability. In saturated conditions, cohesion contributes to overall shear strength alongside friction. Conversely, in unsaturated soils, changes in moisture can reduce cohesion, leading to lower shear strength and increased risk of failure. Understanding this relationship is crucial for predicting soil behavior during various loading scenarios.
• Discuss the role of cohesion in consolidation tests and its influence on settlement calculations.
  • During consolidation tests like the oedometer test, cohesion is vital for understanding how soil will respond to applied loads over time. Cohesive soils exhibit a significant amount of compressibility due to their cohesive properties, which impacts both immediate and primary settlement. The ability of these soils to retain moisture also plays a role in their consolidation behavior; thus, analyzing cohesion helps predict long-term settlement outcomes accurately.
• Evaluate how changes in drainage conditions can affect cohesion and ultimately lead to slope failures or instability in retaining walls.
  • Changes in drainage conditions can significantly alter cohesion by affecting the moisture content within the soil. When water saturates cohesive soils, it may reduce internal friction and cohesion, increasing the likelihood of slope failures or retaining wall instability. An increase in pore water pressure reduces effective stress, weakening the soil structure. Understanding these dynamics is crucial for engineers to design stable slopes and walls that can withstand such variations.

Related terms

Shear Strength:

The resistance of soil to sliding or deformation, primarily influenced by cohesion and friction between particles.

Capillarity:

The ability of water to move through soil pores due to surface tension, affecting soil moisture and cohesion.

Soil Suction: The measure of the water potential in soil, influencing moisture retention and the interaction between soil particles.