We are using Plaxis to assess the settlement of an embankment on firm to stiff clay soils in which the long term settlement is critical for an acceptable design. We are adopting the Hardening Soil Model with Small Strain Soil Model and are a bit confused on the value of power m to adopt for are soil due to varied understanding of the use of this parameter.
Understanding 1: this parameter is used to represent the increasing stiffness Eur with depth and cam be adjusted to mimic the actual variation in stiffness parameter with depth. Where there is no variation with depth a very small value of 0.001 can be adopted. True or false
Understanding 2: Adopt a value between 0.5 and 1 (or default value 0.5) to inform the variation in unload reload stiffness values based on the stress variation. This does not have anything to do with stiffness variation with depth but all to do with the stiffness values to be adopted at different stress levels. If so how do we model the variation in stiffness with depth.
Dear Umair,
I strongly advise checking the documentation about the Hardening Soil model. We also provide information in our Material Models manual.
The power m parameter is defining the amount of stress-dependency of the soil you are trying to simulate. Using a value of 1 means having a linear stress-dependency and a value of 0 means no stress-dependency of the stiffness.
Typically we do not recommend any values as this should be a product of laboratory investigation and based on the experience of the geotechnical engineer, however, for some clays, the value tends to be reaching a linear stress-dependency. Please be aware that the response from soil to soil can, of course, be different, therefore any values that work for some users on one side of the world might not be relevant to other users.