The compaction behavior and permeability evolution of broken rocks: Mechanical model and prediction

This paper proposed a conceptual model of broken rock mass compaction based on elastic theory by simplifying this compressing process and assuming the connection is a similar cubic mass without huge void space. With this simplification, the stress-strain constitutive law is established. The compacted rock mass permeability evolution was modeled based on the cubic law of porosity and permeability. The mechanical model was coupled into permeability evolution model. The predicted permeability evolution by coupled model is similar with reported experimental results. The modeled permeability results were indirectly validated using the weak sandstone input parameters. Compared to intact rock mass, we found that the stress-strain curve of compacted rock mass takes a longer stress-strain path to reach the linearity due to the void space compaction resulted from the friction slipping and re-arrangement of grains. It was also found that the grain elastic modulus does not contribute to the overall bulk compaction and permeability reduction at the initial compaction stage and it will control the permeability evolution only after the broken rock got fully compacted when it can be treated as intact rock mass. The proposed models will potentially lay foundation for the future permeability and caving behavior characterizations using numerical simulation for complex gob area.