Recent Developments on Rock Mass Stability Investigations Associated With Surface and Underground Excavations in Three Dimensions

Deformation and stability of rock masses in underground and surface mine excavations depend on the following factors: 1. Lithological system that exists in the rock mass; 2. Major discontinuity geometry system (large scale features) of the rock mass; 3. Minor discontinuity geometry pattern (small scale features) that exist in each lithology; 4. Intact rock and rock mass physical and mechanical properties of each lithological unit of the rock mass; 5. Mechanical properties of the discontinuities of the rock mass; 6. In-situ stress system of the rock mass; 7. Applied boundary conditions to the rock mass; 8. Water conditions in the rock mass if applicable and 9. Dynamic loading conditions which may be applicable to the rock mass due to blasting and earthquakes. Usually the lithological system and the major discontinuity pattern that exist in the rock mass are very complex. Currently available sophisticated, powerful three-dimensional (3-D) stress analyses software do not have the capability of modeling such complexity. Therefore, the lithological system and the major discontinuity network should be modeled separately before importing them to 3-D stress analyses software to perform 3-D discontinuum stress analyses. Examples of such modeling through previously conducted case studies will be covered in the presentation (Xu et al. 2011,Kulatilake& Biao 2015,Xing et al. 2018). Sampling of minor discontinuity geometry data either through manual or remote fracture mapping techniques is subject to sampling biases. In addition, minor discontinuity geometrical parameters exhibit high variability. Therefore, sampling bias corrections need to be applied using geometrical probability techniques before inferring probability distributions for each of the minor discontinuity geometry parameter using probability and statistical techniques. It is important to note that such procedures are not available in the 3-D stress analyses software available at present. Therefore, modeling of discontinuity minor discontinuity geometry parameters need to be performed separately before importing the results of them to 3-D stress analyses software.