Identifying the critical mechanisms for rock engineering design

In this paper, a methodology called 'mechanism pathway analysis' (MPA) is introduced. The methodology has been developed to support rock engineering design and treats rock engineering as a system, considering all the mechanisms simultaneously operating in the system and how they contribute to determining the rock mass response to engineering perturbations. Through a mechanism network, structured by system variables and binary mechanisms, all the mechanism pathways are searched and their effects are integrated to form the global interactions between all pairs of variables in the system. By studying the pathways and the global interactions, the critical mechanism combinations and hence the principal problems for rock engineering design in any given project can be identified. The methodology can be applied to all rock engineering problems. The procedure for implementing the approach is illustrated by a case example of identifying the key mechanisms in designing unlined rack storage caverns for pressurized-gas storage. Fourteen state variables are used to describe the gas storage system, the interactions between these variables are established and the global influences of the variables are assessed. Closed pathways, i.e. feedback loops, are often critical mechanism pathways and are identified in this case example from the variables 'grouting' and 'temperature'. Critical pathways from 'water pressure' to 'displacement' and from 'stress' to 'displacement' are also identified.