Similarity simulation study on permeability of protected coal seam volumetric strain during mining protective coal seam

The protection effect analysis is one of the key technologies of mining protective coal seam,and volumetric strain and permeability are the core indexes for evaluating the protective effect.Taking No.3 coal seam mining protective coal seam and gas disaster prevention of Changping Mine as the project background,the volumetric strain feature was applied to study the protected coal seam evolution rule of permeability on laboratory similarity simulation study platform. The method of “four point surrounded area” was put forward,which was applied to study the feature of volumetric strain in protected coal seam under the condition of mining stress changing. The mathematical model correlation between volumetric strain and permeability was established,and the permeability evolution of pressure-relief coal and rock mass during mining protective coal seam was revealed. The research results showed that the volumetric strain of protected coal seam in the space showed ∧ shape,π shape and saddle shape during the process of lower protective coal seam; the maximum compressive deformation rate of protected coal seam was 0.723% and the maximum expansion rate was 0.77% during the process of mining protective coal seam. During lower mining protective coal seam,the permeability evolution rule of protected coal seam showed saddle shape,the permeability of protected coal seam in tensile creep phase reached up to 129%,the permeability reached up to 82% on average in the compaction of the overlying strata in the goaf,the permeability increased by 43% after compression on average. The research results revealed the evolution feature of permeability of protected coal seam during mining protective coal seam under Changping Mine and provided theoretical basis for protected coal seam about the pressure-relief effective evaluation and pressure-relief gas extraction scheme.