Dilatancy tendency

Definition

Dilatancy tendency refers to the behavior of certain materials, particularly granular soils, where an increase in volume occurs when subjected to shear stress. This property is significant in understanding how soil responds under different conditions, especially in relation to factors like drainage conditions, soil type, and stress history. When materials exhibit dilatancy, they may initially resist deformation but then become more unstable under sustained loads, affecting their shear strength characteristics.

5 Must Know Facts For Your Next Test

1. Dilatancy tendency typically occurs in saturated granular soils where increased stress leads to volume expansion instead of immediate failure.
2. The phenomenon is most pronounced in dense, non-cohesive soils like sands and gravels, which can exhibit significant changes in behavior when subjected to shear forces.
3. In dilatant soils, the initial increase in volume can lead to a reduction in effective stress, which can ultimately trigger failure if the shear strength is exceeded.
4. Understanding dilatancy is critical for predicting soil behavior during rapid loading events, such as earthquakes or landslides, where rapid changes in pore pressure occur.
5. Dilatancy tendency can be influenced by drainage conditions; undrained conditions may suppress dilatancy effects, while drained conditions often highlight them.

Review Questions

• How does dilatancy tendency influence the shear strength of granular soils under different drainage conditions?
  • Dilatancy tendency can significantly impact shear strength depending on whether the drainage conditions are drained or undrained. In drained conditions, dilatancy leads to increased volume and potentially lower effective stress, which can reduce shear strength and promote instability. Conversely, in undrained conditions, the buildup of pore pressure may inhibit the full effects of dilatancy, leading to different strength characteristics and behavior during loading.
• Evaluate the role of soil type in the expression of dilatancy tendency and its effect on engineering applications.
  • Soil type plays a crucial role in how dilatancy tendency manifests. For instance, dense granular soils such as sands exhibit pronounced dilatant behavior under shear stress due to their particle arrangements and lack of cohesion. This is essential for engineering applications as it influences foundation design and slope stability assessments. Engineers must account for these behaviors when designing structures in areas with granular soils to prevent failure due to unexpected increases in pore pressures during loading.
• Synthesize knowledge about stress history and its impact on dilatancy tendency as it relates to the overall stability of soil structures.
  • Stress history affects how a soil exhibits dilatancy tendency by determining its current state of stress and prior loading experiences. Soils that have been heavily loaded previously may show reduced sensitivity to dilatant behavior due to plastic deformations that have occurred. Understanding this relationship is vital for engineers as it helps predict how a soil structure will respond under new loads or environmental changes. If the stress history is not adequately considered, designs may overlook critical stability concerns arising from dilatancy effects.

Related terms

Shear Strength:

The maximum resistance of a soil to shear stress, which is influenced by factors like cohesion and internal friction.

Cohesion:

The force that holds together particles in a soil mass, contributing to its overall strength.

Effective Stress:

The concept that describes the stress carried by soil skeletons, factoring in pore water pressure, crucial for understanding soil behavior under loading.