Model Behavior
The Nonlinear Elastic Model is characterized by hyperbolic nonlinear elastic behavior. The corresponding stress-strain relation is shown in the figure below.
A. Reversible, elastic stress states
The model shows elastic behavior of the stress-strain relation characterized by a variable modulus of elasticity. It describes the soil behavior for oedometric conditions, that is, those in which the horizontal displacements are negligibly small compared to the vertical ones.
B. Stiffness
Stress dependency:
The material model is able to represent the stress dependency of the stiffness of the soil. Soil shows higher stiffnesses for greater stresses. This property is represented by the function for the oedometric module, as follows:
In addition to the shear strength parameters c and φ, the following characteristic values are required to represent the stress dependence.
| Variable | Meaning |
|---|---|
| Eoed,ref | Tangent modulus determined from the oedometer test for a particular reference stress value. |
| pref | Reference stress for the stiffness modulus. |
| m | Exponent that controls the stress-dependence of the stiffness modulus. It can be measured in both the oedometer test and the triaxial test. |
Dependency on load direction:
Furthermore, the material model considers the dependence of the stiffness on the load path. The soil shows significantly higher stiffness in the case of unloading and reloading compared to the first loading. This property is achieved by a modified oedometric module for unloading and reloading, which results as follows:
Small strain stiffness:
In the material model, you can activate the consideration of the higher stiffness in the area of small strains ("Small Strain Stiffness"). The small strains form an additional state variable for this. The figure below shows schematically the dependence of the stiffness on the mobilized strains.
C. Irreversible, plastic stress states
The model does not represent failure criteria and plasticity.
Suitability
The nonlinear elastic model described above can represent essential soil material properties, such as stress dependency and load path dependency, and is thus suitable for deformation analyses. It is valid for problems for which the assumption of oedometric conditions applies, as well as for stress states at a distance from the load limit.
Application areas are settlement calculations of spread foundations and under dam fill with distance to the failure case.