Study on Reconstituted Coal Damage Features During Unloading Process

Based on the unloading mechanics path of the fixed axial displacement and the unloading surrounding pressure, the study on the damage features durin g unloading process was conducted on the reconstituted coal with high plasticity with CT value, CT damage and CT image of each scanning layer obtained from CT ima ge experiments.The study showed due to the coal heterogeneity and the error of sampling, under the condition of the same stress status, there was a certain difference in the CT value of different areas in the scanning layer center between different scanning layer and the same scanning layer distance.The CT value during unloading pr ocess would be steadily reduced.With the damage steadily accumulated, when the development was at a certain stage, the CT value would be highly reduced and the macro cracks occurred .At the initial unloading period, the CT damage variation was not clear.When the macro cracks occurred, the CT damage would be highly increas ed.During the unloading process, ringlike relaxations occurred at the internal low density end of the reconstituted coal and the normal cracks occurred at the high densit y end.Meanwhile, the macro cracks of the reconstituted coal would be firstly occurred in the low density section, would be in a reversed cone distribution axially and the n would be developed to relative high density area.The experiment results would provide guidance to understand the permeability of reconstituted coal and gas emissio n law of working face.