Experimental study of the dynamically induced rockburst of a rock wall with double free faces

Dynamic disturbance is regarded as one of the most significant factors that induce rockburst around the boundary of underground excavation, particularly in high confining pressure conditions. In the present study, three types of dynamic loading tests are conducted to investigate the dynamically triggered rockburst behavior of a rock wall with double free faces. The three types of dynamic loading considered are the large stress single-pulse loading (mild-disturbance), the middle stress low-frequency cyclic loading (modest-disturbance), and the small stress high-frequency cyclic loading (weak-disturbance). The experimental results are analyzed and the damage evolution process during the dynamic disturbances is described. The tests reveal that the failure strain (i.e., the strain at unstable failure) of the dynamically triggered rockburst is greater than that of the self-initiated rockburst. The intensity of rockburst depends not only on the initial static stress level but also on the dynamic disturbance type. The rockburst induced by the mild-disturbance is mainly related to large amounts of disturbance energy imported. The rockburst caused by the modest-disturbance is contributed by the disturbance degradation of ultimate energy-storage capacity of specimen. The rockburst in a weak-disturbance specimen is primarily due to the disturbance aggravation of the damage in specimen and the elastic strain energy release. In particular, the rockburst hazard from the double free faces is more likely to be triggered and its result more serious than that of the rock structure with only one free face because the increasing free face decreases the rock strength. The fragmentation of the dynamically induced rockburst is larger than that of the self-initiated rockburst. With increasing time of dynamic loading, the damage induced by the modest-disturbance and the weak-disturbance first increases continually, subsequently increases steadily, and finally increases drastically. By contrast, the damage of the specimen under the mild-disturbance condition has a linearly increasing trend.