in computing back analysis of failure case, the validation in this model was SF less than 1. when I decreased the GSI (because the method material was Hoek-Brown), it resulted in the error code 101 in plastic computation. How could I validate the site deformation with the computational deformation from the new GSI, if that error happened to my model?
Dear Ifa,
A safety factor lower than 1.00 means that there is failure taking place even in the previous phase (here gravity loading). By decreasing the GSI you make the rock material even weaker which will also result in continuing to have failure in the model.
I would recommend checking what is being modelled in InitialPhase. You may need to consider multiple phases to simulate the actual case and then perform a safety analysis starting from the last phase.
In order to find out what the mechanism for failure is, and so possibly determine the cause, these Output plots should be inspected:
A combination of these plots will usually give insight into what is happening.