Study On Stability Of Tunnel Surrounding Rock Under Blasting Load

As an important part of China’s transportation construction system,tunnel plays an indispensable role in daily production and life.During the large volume earth rock blasting operation of shallow hole in the open air,the blasting seismic wave propagates from the center of the blasting source to the adjacent tunnel,resulting in blasting vibration effect,which changes the stress state in the surrounding rock of the tunnel.Especially under the cumulative effect of long-term blasting load,the tunnel surrounding rock structure is prone to instability and damage,threatening the safety of people’s lives and property.Therefore,it is of great significance to study the failure forms of surrounding rock under blasting load and the response characteristics of initial support.Based on the results of indoor rock mechanics tests and the monitoring data of blasting vibration signal at construction site,the paper studies the stability of tunnel surrounding rock before and after blasting load by means of theoretical research,field monitoring and numerical simulation calculation.The main research contents and achievements are as follows(1)Based on the investigation and study of the working environment during the blasting construction of x518 Township Road in the section of K1+380 ～ K1+400,the blasting vibration signal monitoring scheme for the tunnel section of K0+150 ～ K0+192 is designed and implemented in the construction site.The peak value of particle vibration velocity,main shock frequency,duration and other relevant parameters at the monitoring point are obtained.Through the first-order linear regression analysis of the peak value of the recorded particle vibration velocity,the Savart formula reflecting the attenuation law of blasting seismic wave is obtained,which provides the basis for future blasting design.Then,the HHT method is used to analyze the measured vibration signal of a blasting at a monitoring point,and it is found that the energy distribution of the monitored signal is relatively concentrated,and the frequency range of the signal distribution is mainly within 120 Hz,which is quite different from the natural frequency of the tunnel structure,so resonance phenomenon is not easy to occur.Using the millisecond blasting construction technology,the instantaneous energy distribution map shows that the energy released by blasting is concentrated in the time period from zero seconds to 50 milliseconds after the explosion,which indicates that the effect of the millisecond blasting technology is not significant enough,and the relevant blasting parameters need to be adjusted.(2)The FLAC3D model of K0+150 ～ K0+170 section tunnel is established.According to the relevant rock mechanics parameters obtained from laboratory test,the rock stratum is assigned.The velocity of particle vibration in the vertical direction at the monitoring point is input to the bottom of the model as blasting load.The displacement field,stress field and plastic deformation field of surrounding rock before and after the initial support of the tunnel are simulated under static and dynamic states The change of sex zone.The influence of single blasting load on the stability of tunnel surrounding rock is weak,and the damage areas in surrounding rock are mainly distributed near the arch wall and floor.However,the current support scheme has limited constraint capacity on the displacement and deformation of surrounding rock,so more effective support measures are needed.(3)Through the monitoring of the clearance convergence rate of the tunnel section after repeated blasting,it is found that the deformation degree of the tunnel surrounding rock exceeds the normal level,which is not satisfied with the requirements of safe construction.The results of numerical simulation show that the convergence rate of tunnel clearance can meet the requirements of safety threshold.