Study On Effect Of Karst Tunnel Blast-vibration Based On Rock Mass Cumulative Damage Mechanism

Under the action of blasting vibration effect,the study on rock mass cumulative damage mechanism has important engineering significance to prevent the abrupt failure of rock mass and to keep a safety tunnel construction and a safe and stable operation in the long-term.Firstly,by analyzing the vibration velocity of the surrounding rock under different times,and combining with the changes of K and ?,the safety velocity and safety allowable distance under the cumulative damage are discussed.Secondly,by improving the safety thickness model between the tunnel and the cave with the accumulation of the slice effect.Finally,by analyzing velocity,displacement and stress of the surrounding rock particle,through the continuous blasting by Midas-NX load simulation,we can draw the following conclusions:(1)The method of velocity vector synthesis and the method of single velocity velocity analysis are used to compare the attenuation law of the blasting vibration with the attenuation index.It is found that the blasting vibration attenuation Jaw of the actual situation of the whole reaction is better,and it can prevent the data is too scattered caused by the error.(2)The seismic wave generated by the tunnel in the karst area will change the path propagation when it goes through the cave,and the formation of the diffraction increases the damage of adjacent tunnel and the surrounding rock,which is not conducive to the overall stability of the cave and is more prone to geological disasters.(3)Analysis of the damage of karst rock from the Hopkinson effect shows that the energy loss of caves and other concealed space free surface is less compared with that of the tunnel face continuous rock mass is smaller,the loss of energy is mainly converted to the particle vibration velocity,and even the formation of rock to fall;micro crack propagation and macroscopic failure.(4)The same explosives to the same geological conditions of the same degree of damage,and there will be safe allowable distance limit after nine times cumulative damage.When the single bursting explosives is 48kg in the tunnel blasting,the safe allowable distance is about 26m under the cumulative damage.(5)The continuous blasting by Midas-NX load simulation,analysis of surrounding rock particle velocity,displacement and stress,Draw the following conclusions:The magnitude of the stress change in the side wall and the tunnel vault position is less than the lower part.In the cavern area,where the cave at the bottom of the tunnel,the structural instability is more likely to occur than cave in the side and top.