Evolution characteristics of deformation and energy fields during coal pillar instability

In this paper, based on the uniaxial compression test of coal samples, the evolution characteristics of deformation and energy fields during coal pillar instability process were studied. Meanwhile, the specimen surface speckles images were recorded by CCD camera. Combined with the monitoring results of coal samples' whole deformation and failure process by using the digital speckle correlation method, the generation and evolution of deformation localization in coal pillar, as well as the characteristics of coal pillar instability in each stage were systematically analyzed. Then, the energy evolution during coal pillar instability process was calculated. The results show that the coal pillar instability can be divided into two types: unstable propagation of fracture inner coal piller and unstable sliding of weak plane inner coal piller. The energy release and accumulation patterns during loading process of coal pillar are mainly controlled by the final instability modes. Comparatively speaking, the energy release rate during the weak plane unstable sliding inner coal piller is relatively small, while the energy release rate during the fracture unstable propagation is larger.