Soil yield is a critical concept in soil mechanics, fundamentally defining the point at which soil begins to deform permanently under stress.
At its core, soil yield is the stage when there is an increase in shear strain with constant shear stress. This definition, as highlighted in the reference, marks a significant transition in the soil's behavior.
Understanding the Yield Point
Before a soil reaches its yield point, it typically exhibits elastoplastic behaviour. This means that deformations are partly elastic (recoverable) and partly plastic (permanent). As stress is applied, both stress and strain generally increase.
However, once the yield point is reached:
- The shear stress remains relatively constant.
- The shear strain continues to increase significantly.
This point signifies that the soil structure is undergoing irreversible changes.
Behaviour After Yielding
According to the reference (30-Jan-2019), once soil starts yielding, all deformations are plastic. This is a key characteristic distinguishing the post-yield state from the pre-yield elastoplastic state. Plastic deformations mean that even if the applied stress is removed, the soil will not fully return to its original shape; the deformation is permanent.
Significance of Soil Yield
Identifying the yield point is vital in geotechnical engineering for several reasons:
- Predicting Deformation: It helps engineers predict when large, potentially unacceptable, deformations (settlement or movement) are likely to occur in structures built on or within the soil.
- Assessing Stability: Understanding the yield strength (the stress at which yielding begins) is crucial for assessing the stability of slopes, retaining walls, and foundations.
- Soil Modeling: Yield criteria are fundamental components of constitutive models used in numerical analysis to simulate soil behavior under various loading conditions.
Practical Implications
Recognizing soil yield allows engineers to:
- Design foundations that avoid exceeding the soil's yield strength under normal service loads, minimizing settlement.
- Analyze the potential for failure in earth structures by determining when critical stress levels are reached, leading to yielding and instability.
- Select appropriate construction techniques and materials based on the soil's yielding characteristics.
In summary, soil yield is the point of transition where soil shifts from exhibiting partially recoverable deformation to purely permanent deformation under stress, specifically defined by increasing shear strain at constant shear stress.
