Experimental study on rockburst and its spatio-temporal evolution criterion in high stress roadway

To study the mechanism of rockburst and its spatio-temporal evolution criterion,the rockburst simulation ex- periment was conducted using granite specimen with a perforated circular hole under different lateral load. Based on the micro camera, acoustic emission ( AE) system and infrared thermal imager, the characteristics of its time-se- quence,time-frequency,time-space and infrared temperature were analyzed during the test. The results demonstrated that the failure could be divided into four stages:quiet period,particle ejection period,stable failure period and col- lapse period. It was consistent with the engineering site. When the surrounding rock of the hole was bent and broken, σθmax ≈ (1． 38 ~ 1． 85)σc . With the growth of the lateral load,the accumulated elastic strain energy grew around the hole area during the quiet period,the energy release rate gradually promoted and the rockburst speeded up during the particle ejection period,the duration of the stable failure period first increased and then decreased. In addition,the lat- eral load first strengthened and then weakened the stability of the pore. The relatively quiet period of AE ringing count- ing rate could be regarded as the precursor signal for hole collapse. The anchor point began to focus locally before the hole failure. After the hole collapsed,the anchor point strip basically coincided with the main fracture surface of the specimen and it formed an “X” shaped conjugate shear fracture around the circular hole. In the stability failure peri- od,the low frequency ratio was accelerated and the high frequency ratio was decreased compared with the particle e- jection period. The stress concentration caused the whole infrared temperature raised gradually and presented the high temperature region nested low temperature zone. Furthermore,when rockburst occurred,the high temperature area mi- grated from the shallow surface to the deep area. Before the hole collapsed,the temperature of the rockburst pit rose sharply.