Application |
PLAXIS 2D PLAXIS 3D |

Version |
PLAXIS 2D PLAXIS 3D |

Date created |
22 September 2015 |

Date modified |
22 September 2015 |

For ** Undrained A** materials, where effective stress parameters are used, the undrained shear strength is not an input parameter but a result of the analysis. In order to check that the shear stress values do not violate the undrained shear strength, the shear stress (σ

_{1}- σ

_{3}) / 2 should be checked against the undrained shear strength s

_{u}(or c

_{u}) in the Output program.

In *Figure 1* the shear stress in Point A is below the given undrained shear strength s_{u} (c_{u}) (from soil test or laboratory tests), and so the undrained shear strength is not violated for this stress state. However, for the second (larger) Mohr Circle, the shear stress in point B is larger than the undrained shear strength, and so the strength criterion is violated.

Figure 1. Mohr Circles for evaluating shear strength

The undrained shear stress in the Output program can be seen via the menu item by selecting:

*Stresses* » *Principal total stresses* » (σ_{1} - σ_{3}) / 2

Then you can select to view the desired results:

- by drawing a
*Cross section* - or by using the
*Hint box*and move your mouse over the area of interest.