Analysis Of The Mechanism Of Structural-slip Rockburst And Catastrophic Processes In Deep-buried Tunnel

At present,the focus of Chinese transportation and hydropower projects is gradually shifting to the southwestern mountainous areas,and a series of major projects related to national rejuvenation represented by the Sichuan-Tibet Railway are under construction or to be constructing.Affected by the developed fault structures and prominent tectonic stress in the southwest region,tunnel projects constructed in hard rock lithological belts are very prone to fracture-slip rockburst disasters.Under the effect of continuous tunnel excavation and excavation disturbance,the change of fault stress state will make the structural-slip rockburst show new characteristics.In this paper,by combining theoretical analysis,laboratory test and numerical simulation,the research on the evolution of fault tectonic stress under the effect of deep tunnel excavation through a large structure plane,the shear slip law of the structure plane considering the effect of continuous excavation,and the research on the mechanism of the structural-slip rockburst,the research on the rockburst criterion of the structural-slip rockburst disaster process and the energy evolution process,and the research on the prevention and control measures of the rockburst have achieved.The following research results were got:(1)When the tunnel is excavated below the structure plane,the normal stress of the structure plane decreases and the shear stress increases;when the tunnel is excavated above the structure plane,the normal stress of the structure plane decreases and the shear stress increases after the tunnel face passes through the structure plane;Under the action of disturbance load,the stress on the fracture surface will fluctuate;Under the effect of continuous excavation,the stress on the structure plane will show the above characteristics constantly,and the closer the working face is to the structure plane,the greater of the stress drop and raise.(2)The shear slip of the structure plane under the conventional stress path can be divided into three stages: stable slip stage,stick-slip stage I,and stick-slip stage II.The stress drop is concentrated at the end of the stable stage and the stick-slip stage II;The higher the strecture plane strength,the greater the stress drop generated during shear failure,the more obvious the AE signal and the sound signal generated with the shear failure,and the more tensile cracks developed wear area,blast crater area on the structure plane.(3)Under the effect of tunnel continuous excavation,the larger the initial normal stress and the disturbance load,the more excavation steps the structure plane undergoes before shear failure,the larger the shear stress drop at shear failure is,and the more obvious failure characteristics are;When the stress adjust after excavation,the AE signal is accompanied,but the AE signal and the sound signal are the most obvious during the shear failure.Under the effect of tunnel continuous excavation,the shear stress drop and the elastic strain energy are lower when the structure plane is failure than that under the conventional stress path.So the structural-slip rockburst are more likely to occur under the effect of tunnel continuous excavation,but the intensity of rockbursts is reduced.(4)During the excavation of a deep-buried tunnel passing through a large structure plane,the surrounding rock near the structure plane has a large displacement,obvious stress concentration,high elastic strain energy density,and a high rockburst proneness.After the structural-slip rockburst,the elastic strain energy is released in large quantities.Based on the characteristic that the elastic strain energy will be released rapidly and in large quantities when the rockburst occurs,a new rockburst energy index NERI is proposed,which considers the energy change process of the surrounding rock during the tunnel excavation.(5)Taking the rockburst section which affected by a larger structure plane of 4#tunnel of Qinling Water Transmission Tunnel as an example,a 3D discrete element numerical simulation was carried out.The results show that the NERI index can more accurately predict the location and grade of the rockburst,and the reliability is high.Comparing the surrounding rock’s NERI of tunnel without support system,and the surrounding rock’s NERI of tunnel after optimizing the excavation footage or laying the bolt-shotcrete support system,it is found that optimized excavation footage can reduce the intensity of rockburst more than that of shotcrete support.There are 101 figures,13 tables,102 references.