Study On The Techniques Of Active Prevention And Controlling Of Rock Burst Based On Controlled Blasting

With the continuous development of China’s comprehensive national strength and the deepening of the western development strategy,there are more and more great underground works in the mountains of the western region of China.With the increasing of its buried depth and the ground stress,rock burst has become a kind of engineering geological hazard which cannot be ignored.There is a certain correspondence between rockburst and blasting in time and space distribution.Based on the anaglysis of the rock burst data of the deep buried cavern group of Jinping II Hydropower Station and the Qinling Tunnel of the West Kang Railway,the difference the in breeding regularity,prevention and controlling of rockburst between TBM and drilling and digging excavation section is drawn as follows:TBM tunneling is more likely to lead to the occurrence of minor rock burst,such as spalling,and the damage range is relatively larger.The drill-blasting method has remarkable advantages in dealing with the construction difficulty and time consuming of rock burst failure under the same conditions.The tunnel face can be closed when the strong rock burst occurred during the drill-blasting method,while it is not possible for the TBM.By summarizing the control blasting parameters of two typical buried underground projects,three influencing factors of controlled blasting are obtained:contour controlled blasting effect,cut blasting form and excavation footage.Based on the analysis of the limitation of the static mechanics mechanism of rock burst in explaining the influence of excavation disturbance on rock burst breeding,it is recognized that the change of the original stress field caused by excavation and the disturbance of the construction process to the surrounding rock can affect the breeding,scale and intensity of rock burst to a certain extent,and then the principle of active prevention and control of rock burst based on the dynamic mechanism is put forward.On the basis of smooth blasting of strong rock burst section in Jinping Ⅱ diversion tunnels,through theoretical analysis and numerical calculation,The relationship between the degree of stress concentration and line charge density is established by theoretical analysis and numerical calculation.Contour control blasting is optimized by stress criterion of rock burst,to further strengthen the drill-blasting excavation transient unloading effect,to improve the degree of stress concentration of the surrounding rock,to reduce the energy storage capacity of rock mass,So as to reduce the stress concentration and rockburst risk to a great extent.The four method,single helix cutting,9-hole cutting,2-hole and 3-hole wedge-shaped cutting,are selected to compare the damage zone,blasting vibration and transient unloading excitation vibration with the numerical calculations,to separate the vibration induced by the transient strain energy release through the time-energy density method for getting the vibration energy excited by blasting and transient release of strain energy.the single helical cutting method should be chosen to ensure enough damage degree of surrounding rock,to reduce the peak value and unloading rate of vibration excited by blasting and transient unloading,and to control the release of energy in the cut blasting section,so as to achieve the purpose of controlling rock burst actively.The TBM excavation can be interpreted as a continuous one in a very small footage on the basis of comparing the energy release rate of different excavation footage.Assuming that the blasting effect is completed instantly in the stress dynamic adjustment process of the blasting excavation,in the numerical simulation,the secondary stress field is instantaneously applied to the excavation boundary at the moment of excavation.The concentration peak and depth of unit strain energy in different excavation footage are compared by presetting damage zones.It is concluded that the TBM is beneficial to the natural controlling of rock burst,but for it,the rock burst can not be actively controlled before it happened.The tunneling rate of TBM construction must be slowed down when the strong rock burst occurred.While it is not necessarily for drilling and blasting method,it can also be used to control rock burst by contour controlled blasting optimization,cutting groove optimization and excavating footage optimizing and so on.