We have used SSR analyses for slopes only, not for underground excavations/tunnels. However, there are people who have used SSR for such analyses.
The following comments are from Evert Hoek regarding the use of SSR in tunneling design (comments are from 2009):
I have thought a great deal about the possible role of SSR in tunnel design and I am afraid that I fail to see much future for it other than that it provides another interesting number. The practicality of tunnelling requires the designer to start off with a number of common sense questions that determine the methods that are best suited to providing a reliable and practical solution. These questions include the nature of the rock mass and in situ stress field and, as a consequence, the most likely failure modes; the method and sequence of excavation and the constraints imposed by this method on the support systems that can be used; the influence of groundwater on the design (for example whether the lining is leaky or impermeable); the role of time (creep and rock deterioration) on the response of the rock mass around the tunnel and the sensitivity of surface structures above the tunnel on the permissible subsidence and tilt. Each underground structure is unique and it is important to determine which of the factors listed above, or others, will dominate the design. There is no single magic bullet for tunnel design and it is usually a combination of methods that provide a number of quantified responses which then have to be assessed as to their adequacy to meet the over design requirements. In some cases these requirements may be dictated by national codes or guidelines.
It is very difficult to see where a "factor of safety" determined by SSR fits into this scheme of things. In fact, it does not answer any of the questions outlined above and the number arrived at may or may not have any physical significance. The sequence of failure, if it occurs, can be adequately assesses by means of the normal pi or modulus reduction techniques that we employ. I always set maximum displacements as the background screen and add failure indicators and boundary displacements. If I am using rockbolts I look at the axial loads in the bolts and whether any portions of the bolts have failed and if I am installing a lining I look at the support capacity plots. For near surface tunnels I look at surface displacements.