卸载过程中型煤损伤特性研究

Study on Reconstituted Coal Damage Features During Unloading Process

基于固定轴向位移卸载围压的卸载力学路径,利用CT扫描试验对塑性较强的型煤进行了卸载过程损伤特性研究,得到了各扫描层CT值、CT损伤及CT图像。结果表明:由于煤样的非均质性及制样误差,同一应力状态下,不同扫描层及相同扫描层距离扫描层中心不同区域CT值存在一定的差异;卸载过程中CT值逐渐减小,随着损伤的逐渐累积,发展到一定阶段时,CT值出现大幅度减小,宏观裂纹出现;卸载初期的CT损伤变化不明显,出现宏观裂纹时,CT损伤大幅度增加;卸载过程中,型煤内部低密度端会出现环状松弛,高密度端出现普通裂纹,同时煤样宏观裂纹首先出现在低密度段且在轴向上呈倒锥形分布,进而向密度相对高的区域发育。试验结果对于理解型煤的渗透特性及工作面瓦斯涌出有很好的指导作用。

Based on the unloading mechanics path of the fixed axial displacement and the unloading surrounding pressure, the study on the damage features during 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 image experiments. The study showed due to the coal heterogeneity and the error of sam- pling,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 process would be steadily re- duced. 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 increased. During the unloading process, ringfike relaxations occurred at the internal low density end of the recon- stituted coal and the normal cracks occurred at the high density 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 then would be developed to relative high density area. The experiment results would provide guidance to understand the permeability of reconstituted coal and gas emission law of working face.