# When using stage factors, what stage are the factors relative to?

In RS2 there is an option to apply a distributed load equal and opposite to the in situ stress, known as induced stress.  Tutorial 33 describes how to apply this type of load.

When you are applying an induced stress, the program computes the stress vector required to balance the stress in the rock/soil, resulting in zero surface deformation.  The stage factor is then multiplied by the stress vector to get the distributed load applied to the surface.  So zero means stress free, 1.0 means the induced stress vector which balances the stress in the rock/soil.

In the example below, the stress applied to the surface is the same in Stage 3 and Stage 4.  The results of Stage 3 and Stage 4 will be the same unless there is a change in loading or excavation between the stages.  For example, if a surface load was applied or an adjoining tunnel was excavated in Stage 4, the results will be different.  It is also important to note that you do not apply an induced stress load in the first stage.  The RS2 file corresponding to this example is attached to this article.  Note that there is both normal and shear applied to the surface.  In general, a normal pressure alone will not balance the induced stress.

Sample Stage Factors (for attached file):

Stage 1:  Factor = 0

Stage 2:  Factor = 1.0

Stage 3:  Factor = 0.5

Stage 4:  Factor = 0.5