A conceptual model to characterize and model compaction behavior and permeability evolution of broken rock mass in coal mine gobs

This paper proposed a conceptual model of broken rock mass compaction based on elastic theory by simplifying the compression process. This conceptual model assumes that the contact connection between two adjacent rock particles is similar to a cubic mass. With this simplification, the stress-strain constitutive law is established. The change in the secant modulus in the mechanical model derived from the variation of the connection coefficient agrees well with the reported experimental results. The permeability of compacted rock mass evolution was modeled based on the cubic law. The mechanical compression model was coupled with the permeability evolution model. The modeled permeability evolution is consistent with reported simulation and experimental results. The modeled permeability results were validated using Karacan's data with broken shale rock properties. Compared to an intact rock mass, we found that the stress-strain curve of a compacted rock mass takes a longer compression path to reach linearity due to the void space compaction resulting from friction slipping and the re-arrangement of particles. It was also found that the particle elastic modulus does not contribute to the overall bulk compaction and permeability reduction at the initial compaction stage. However, the particle elastic modulus controls the permeability evolution for a fully compacted gob, where the gob can be treated as an intact rock mass. The proposed conceptual models will potentially lay the foundation for future permeability and caving behavior characterizations using numerical simulations for complex gob areas.