Application |
PLAXIS 2D PLAXIS 3D |

Version |
PLAXIS 2D PLAXIS 3D |

Date created |
11 September 2014 |

Date modified |
11 September 2014 |

Both the 2D and the 3D program allow for input of volumetric strain in x,y and z direction. Alternatively you may directly specify a volumetric strain (ε_{vol}) which basically means that the specified strain is equally distributed in x,y and z direction, i.e. ε_{xx} = ε_{yy} = ε_{zz} = ε_{vol} / 3.

When applying a volumetric strain to a cluster the following procedure is followed:

- first the program expands or contracts the relevant cluster according to the applied strain while maintaining the same stress level in this cluster;
- next the reaction stress/force coming from the surrounding soil and/or boundary conditions is determined based on this change in strain;
- then the unbalance due to this reaction stress/force is solved in the model introducing deformations which in the end may cause a lower strain to be calculated in the cluster with the applied volumetric strain;
- finally a stress equilibrium is found between all the relevant clusters and/or boundary conditions.

So realise that the stiffness ratio between the cluster with volumetric strain and its surrounding clusters determines the final deformations and stress levels.

In example: let’s assume a cluster with stiffness E1 which has a certain applied volumetric strain and the surrounding clusters with stiffness E2 with no applied volumetric strain.

Now for the following cases we find:

- if E1 >> E2: then ε
_{vol,calculated}= (approximately) ε_{vol,applied} - if E1 << E2: then ε
_{vol,calculated}= (approximately) 0