Experimental study on the secondary breakup properties of crushed coal through a dynamic porosity model based on Weibull distribution theory

Abstract Secondary breakup of the residual coal in goaf caused by periodic weighting changes its gradation, coal-oxygen contact area, stacking structure, etc. It cannot be ignored in studies of spontaneous combustion and compaction character of bulk coal. This paper developed a new dynamic porosity model employing the Weibull function based on the quantitative results of the secondary breakup phenomenon. A precise three-stages compaction process (particles self-organization and re-accumulation stage, secondary breakup stage, and simultaneous compression deformation stage) was observed and designated by this model. The competition mechanism among the deformation modes of coal particles during axial compaction was discussed. The main findings are as follows: (1) The formation mechanism of the stage characteristics in the compaction process for broken coal was actually a competition among the three deformation modes (secondary breakup, inter-particle self-organization, and inter-particle extrusion). (2) The proposed model allowed a finer division of the three stages of compaction from the perspective of the various deformation modes of coal particles. (3) The intensity of secondary breakup was weaker in the early and late stages of compaction and made no dominant contribution to deformation. A secondary breakup–dominated deformation stage was derived through comparing the proposed model with experimental data. (4) In the aforementioned deformation stage, the average relative error between the model’s predictions and the experimental data was 4.63%.