Rock mechanics interaction matrices offer a convenient way of summarizing the key geomechanical parameters in a rock engineering project. By quantitatively coding the interactions in such a matrix to reflect their importance, or significance, in terms of generating a hazard, it becomes possible to determine the significance of a series of interactions. Such a series represents a pathway through an interaction matrix, and by comprehensively identifying all such pathways and computing their intensity as the product of the interaction significance values, hazards can be identified. Depending on the geometric mean of the interaction values, interaction matrices are seen to be either amplifying or attenuating. Pathways of various lengths can be studied, and it is found that a distribution of pathway intensity values exists for each pathway length. These distributions tend to contain many low-intensity pathways, with a small number of high-intensity pathways that can be readily identified and subjected to further analysis if required. An illustrative example based on the problem of hazard identification for underground nuclear waste repositories is used to show how the technique can be applied to problems of a realistic size. Of the 1470 3-interaction pathways occurring in a 7 × 7 interaction matrix, 6 were found to be the most critical.
Identification and quantification of hazards in rock engineering is a formidable task, and is one that requires both sophisticated analytical tools and a large amount of geomechanical data if it is to be performed in any sort of mechanically rigorous sense. At the early stages of a project neither of these may be available, and this lack may be compounded by the fact that a number of candidate sites may be under preliminary investigation. Such constraints suggest that a simplified and rapid form of identification and quantification may be useful.
One approach to identifying the hazards that can occur during rock engineering construction is to understand the interactions that take place between fundamental parameters. Thus, for example, we may wish to investigate the specific effect that construction blasting may have on groundwater flow, and what hazard this may lead to. This approach of studying the interaction between fundamental parameters is the basis of Rock Engineering Systems [1, 2], whereby the main parameters and their interactions are conveniently recorded in a rock mechanics interaction matrix. This approach, together with the interaction matrix concept, has found application in hazard and risk assessment across the spectrum of engineering geology and rock mechanics. Examples include rock fall analysis , slope instability [4, 5], and geotechnical hazard assessment for the use of tunnel boring machines