Study On Time-lag Characteristics And Mechanism Of Rock Burst In Tunneling Roadways

The rock burst disaster in coal mines in China is becoming more and more serious.The number of rock burst disasters in tunneling roadway accounts for a large proportion of all that,leading to a number of death and injury accidents.The research on the occurrence mechanism of rock burst in tunneling roadway is of great significance for rock burst mitigation.The rock burst in tunneling roadway generally has the characteristics of time-lag.Whereas,considering the time-lag,the research on the initiation process,occurrence mechanism and prediction model of time-lag behavior of rock burst in tunneling roadway is still insufficient.Therefore,by means of statistical analysis,similarity simulation,field measurement,laboratory test,numerical simulation and theoretical analysis,this thesis studies the time-lag characteristics and mechanism of rock burst in tunneling roadway.The main conclusions are as follows:(1)The rock burst occurrence area of tunneling roadway is generally far away from the heading face of tunneling roadways.And there is no or small bursting damage near around heading face.Among them,the number of cases that do not destroy near the heading face accounted for about 68%.In space,the rock burst in the tunneling roadway mainly occurs in the stress adjustment section after the opening excavation.The length of the adjustment section of tunneling roadways has a positive correlation with the excavation speed,a negative correlation with the coal and rock strength and support strength.(2)Using similarity simulation,earth-sound monitoring,drilling imaging and electromagnetic wave CT detection,the measurement in actual engineering proves that,the deformation evolution of surrounding rock in tunneling roadways can last more than ten days,with obvious time effect and stage characteristics.The cumulative damage degree of surrounding rock in tunneling roadway is approximately negative exponential relationship with exposure time.In time,it mainly occurs in the stress adjustment period after the opening excavation.The length of adjustment period is less affected by excavation speed.(3)The influence law of factors such as in-situ stress,geological structure,dynamic load disturbance on the shock appearance characteristics is studied,and the load source characteristics of the rock burst in tunneling roadway are obtained.The number of rockburst induced by mining stress accounts for 85%,occurring in shallow and deep coal seams.The number of rock burst induced by in-situ stress accounts for15%,occurring in coal seams with large buried depth and high stress.The load source of rock burst in tunneling roadways has the characteristics of "high static load and low dynamic load",and the weak dynamic load disturbance mainly plays a triggering role.(4)The damage evolution models in the steady or unsteady state of surrounding rock in tunneling roadways are established to describe the characteristics of loading and unloading,elastic-plastic transformation,energy accumulation and release of surrounding rock.The damage evolution process of surrounding rock in tunneling roadways is accompanied by complex loading and unloading action.The loading and unloading rate of shallow surrounding rock is greater than that of deep surrounding rock.The shallow surrounding rock is damaged before the deep surrounding rock,when it reaches the peak strength.The energy storage level and release intensity during damage and failure process are relatively low,with low possibility of rockburst occurrence.The loading and unloading rate of deep surrounding rock is relatively small,the loading and unloading duration is longer,the energy storage level is higher,it is easier to cause rockburst,and the occurrence intensity of bursting failure is greater,and the situation of bursting occurrence is farther away from the heading faces.There is space effect excavation heading in the tunneling roadway,with the lower stress and energy evolution intensity of the surrounding rock in the excavation influence area than that in the non-excavation influence area,and thus surrounding rock in the excavation influence area has more possible to meet the conditions of rock burst compared with the surrounding rock outside the influence area.The type of in-situ stress field has a profound impact on the difference of surrounding rock damage evolution characteristics in different directions.The surrounding rock with higher elastic energy accumulation level in the direction of the maximum principal stress and stress concentration is more prone to rockburst initiation.(5)The discontinuous characteristics of surrounding rock stress and elastic energy density and their influencing mechanisms on rock burst are analyzed,and a quantitative expression for the time-delay characteristics of rock burst is established.Under the action of typical loading and unloading paths of surrounding rock of tunneling roadway,the bursting potential coal is mainly characterized by elastic-brittle deformation and failure.At the interface between the rock failure zone and the elastic zone,the distribution of stress and elastic energy density is discontinuous,and both form "cliff" jump,which provides force source and energy source for the occurrence of rock burst.Based on the relationship between surrounding rock damage and time,damage variables were introduced to establish the quantitative characterization relationship of stress,energy,range of failure zone and time in the evolution process of surrounding rock in tunneling roadway.(6)The rock burst prediction model of ideal elastic-brittle coal roadway based on instability coefficient and energy coefficient is constructed,which can represent the change of rock burst risk during the evolution of roadway surrounding rock.In the range of surrounding rock adjustment section of tunneling roadway,as far away from the head,the energy coefficient and instability coefficient of surrounding rock are increasing,and the risk of rock burst is also increasing.The more brittle the coal body is,the higher the initial stress is,the higher the impact risk degree of driving roadway is,the larger the impact risk range is,and the smaller the range of no rock burst near the head is.The impact degree of support strength on impact risk is relatively small,only when the support strength exceeds a certain critical value,the increase of support strength will reduce the impact risk range.(7)The theoretical research results in this thesis was adopted to predict the rock burst of driving coal roadway in 401102 working face of Mengcun coal mine in Binchang mining area.The prediction results are basically consistent with the actual situation on site.Then techniques such as avoid the layout of coal roadway dodging high stress area,drillhole and blasting pressure relief and the support and so on are put forward.