Investigation On Inoculation Process And Early Warning Of Delayed Rockburst In Deep Buried Tunnel By Acoustic And Electrical Monitoring

In recent years,with the rapid development of our society and economy,a large number of water conservancy and hydropower construction projects are also in full swing.As more and more underground space has been developed and utilized,these hydropower projects are inevitably carried out to the deep,thus encountering many deep rock mechanics problems,of which rock burst is the most prominent and the harm is quite huge.Rockburst is violent and sudden,which often threatens people's personal and property safety.However,the delayed rockburst occurs only after the excavation and unloading is completed,and the time is often delayed,which makes people feel that the hazards of rockburst have been relieved and thus become more hazardous.According to statistics,many underground projects at home and abroad have time-delayed rockburst phenomenon,which has also received widespread attention from underground engineering scholars,but at present there is no consistent understanding of its formation and occurrence.Based on the micro-earthquake monitoring project of Qinling tunnel in the Hanjiang-Weihe diversion project,this paper analyzes the characteristics of specific delayed rockburst cases through acoustic and electrical monitoring,and explores new ideas for the preparation process and early warning of delayed rockburst.The main results of this paper are as follows:(1)Before the occurrence of delayed rockburst,there is an incubation process:microcracks in surrounding rock continuously initiate,expand and penetrate,eventually forming macroscopic cracks,accompanied by a large number of microcracks that can be monitored by microseismic and electromagnetic radiation equipment.(2)Most of the time delay type occurs in the relatively complete tunnel section of the rock mass with certain support strength,with a small amount of joint fissures inside the rock mass,and the microseismic events are more active during excavation,but its strain energy has not been fully released,and may be accompanied by the formation of block blasting blocks.(3)The main distribution range of microseismic events after excavation unloading is between-2D and 3D.The influence range of excavation unloading of this tunnel is concentrated in the range of about 18m behind the face and 20m in front of the face,and it is concluded that the rockburst occurring after excavation unloading for 4d is time-delayed rockburst.(4)The correlation analysis of logEI,?V_A and b values for the early warning of time-delay rockburst is made.It is concluded that the higher logEI decreases rapidly,the rapid increase of?V_A and the rapid decrease of b value can be used as precursor information for the occurrence of time-delay rockburst.(5)The dynamic non-contact monitoring of electromagnetic radiation can preliminarily predict the range of time-delay rockburst danger zone.At the same time,the variation trend of electromagnetic radiation intensity and pulse number in the dynamic monitoring area with time is similar to that of"big M"type.When the electromagnetic radiation intensity and pulse number increase significantly,there is rockburst risk.(6)EMR,N,?b,?LogEI and??VA as the main control factor of delay rockburst criterion.At the same time,using fuzzy mathematics combined with acoustoelectric monitoring to study the rockburst problem can obtain more reasonable results.