Abstract
In view of the phenomenon of ultra-large drilling cuttings quantity in rockburst coal seams, the concept of ultra-large drilling cuttings quantity has been proposed. A plastic damage strain sof-tening mechanical analysis model for coal seam drilling cuttings hole has been established. Us-ing the disturbance-induced instability theory, we investigate the mechanism of the ultra-large drilling cuttings quantity in coal and derive an analytical solution for its triggering conditions. The main influencing factors of the ultra-large drilling cuttings quantity phenomenon and its relationship with rockburst have been analyzed. The research results show that: the phenome-non of ultra-large drilling cuttings quantity occurs under various conditions, such as different mine depth and different strength of coal bodies, and is the result of disturbance and instability of the drilling cuttings hole structure, which is different from gravity-induced collapse and gas or stress-induced blowout. The initiation conditions for the ultra-large drilling cuttings quantity phenomenon in coal are mainly controlled by the bursting energy index KE and compressive strength σc. The larger the bursting energy index KE , the smaller the critical stress for the initia-tion of the ultra-large drilling cuttings quantity phenomenon, making it more likely to occur, conversely, the larger the compressive strength σc, the larger the critical stress required for the initiation of the ultra-large drilling cuttings quantity phenomenon, making it less likely to oc-cur. The bulk density of the coal only affects the critical value of the ultra-large drilling cuttings quantity and does not change the critical stress for the initiation of the phenomenon. The ul-tra-large drilling cuttings quantity in coal is sudden and locally destructive, more likely to occur in brittle coal or soft coal but can be more severe in hard coal. The initiation conditions for ul-tra-large drilling cuttings quantity in coal share the same controlling factors and patterns of change as the occurrence conditions for rockburst. When the ultra-large drilling cuttings quan-tity phenomenon appears in a borehole, the stress in the surrounding rock of the roadway has reached the critical stress level necessary for a rockburst to occur. This indicates that the ul-tra-large drilling cuttings quantity phenomenon can serve as a dynamic phenomenon to assess the burst risk of the roadway.