Abstract: The mechanical properties of the regenerated rock mass are intrinsically changed due to the reorganisation of the structure and components in the coal mine. In this study, the fractured rock mass was repeatedly compressed during the compaction and diagenesis process of the regenerated rock mass. Then the fractional compaction test under confined conditions was carried out using the broken surrounding rock of the regenerated roof of the Zhoujing coal mine in Guangxi. The results show that the process of fractional compression can be divided into three stages: compaction crushing, compaction stress memory and compaction consolidation. At the first compression, the compacting characteristic curve changes linearly, and the subsequent compaction curve gradually changes to an exponential form, while the stage of compaction stress memory shows a polynomial change. Under the confined compression condition, the criterion of minimum potential energy is used to determine the crushing fracture of irregular rock samples. The compression characteristics of fractured rock samples are influenced by the number of compaction and the height of rock mass. When the times of compaction are larger, the cumulative compression strain is greater, and the stress increment in the subsequent compression is higher. As the loading height is higher, the cumulative total strain is greater at the same compressive stress. When the compaction stress reaches a certain degree, the grain-size distribution of the broken rock samples with different coarse-grained sizes tends to be consistent. Therefore, the correlation between the size distribution of broken rock samples and the compaction degree of the regenerated rock mass is established.

Key words: broken rock, fractional compaction, compaction characteristics, particle size distribution