Study On Dynamic Response Mechanism Of Tunnel Blasting And Spatial Variation Characteristics Of Surrounding Rock

With the large-scale construction of expressways,in order to shorten the highway mileage,adapt to the mountainous terrain,save investment,reduce the occupation of arable land or facilitate the smooth horizontal curve of the highway,the current proportion of highway tunnels is increasing.In Guizhou area,the strength of the surrounding rock of the mountain is relatively high,and most of them adopt the drilling and blasting method to carry out the tunneling construction.However,due to the vibration of surrounding rock caused by blasting,the drilling blasting method has a great impact on the deformation and damage of surrounding rock.Therefore,studying the stability of surrounding rock in drilling and blasting construction has important practical significance.Taking laomu tunnel project of Guizhou Dalong expressway as the background,the vibration and deformation parameters of surrounding rock during blasting construction are monitored through on-site measurement and setting out,borehole charging and blasting program,and the dynamic response mechanism is studied based on the obtained data;three different load waveforms,i.e.exponential load,smooth curve load and triangle load,are respectively studied The wave form is analyzed and simulated by FLAC3 D software.Finally,the deformation of surrounding rock measured in the project is compared with the numerical simulation results.From the aspects of charging mode,initiation direction,support method and so on,the targeted reinforcement method is proposed to control the damage of surrounding rock caused by blasting load,collapse of rock mass and falling off of separated layer,so as to improve the integrity of surrounding rock and realize the whole initial stage Coupling of stage support structure.The results show that the blasting parameters are the key factors to determine the dynamic effect of blasting;the increase of charge will increase the peak value of blasting load,and the increase of peak value will lead to the increase of the degree of surrounding rock fragmentation,and the main role of surrounding rock by blasting is blasting vibration.The damage stress is mainly shear stress in Z direction in space.The maximum displacement of surrounding rock occurs in the vault under the action of blasting.Based on the magnitude of vault displacement,the displacement area can bedivided into five influence areas with different displacement degrees.The distribution of influence areas shows that the deformation of surrounding rock is larger when it is closer to the explosion source,and the displacement of surrounding rock decreases with the distance increasing.Among the three different load waveforms of exponential load,smooth curve load and triangle load,the exponential load waveform is more complete than the smooth curve load and triangle load waveform to show the spatial variability characteristics of surrounding rock,and the deformation size is close to the actual working condition.The uncoupled charging and reverse initiation can fully break the rock mass,penetrate the external cracks and reduce the damage caused by the shock wave to the internal of the surrounding rock.Before and after support,the plastic zone of surrounding rock changes obviously,and reasonable support mode can effectively improve the stability of surrounding rock.Under the combined action of concentrated load and continuous blasting dynamic load,the internal damage of rock mass is accumulating continuously,and the scope and depth of surrounding rock fragmentation and expansion are increasing continuously.Strengthening the support mode of arch crown can effectively reduce the collapse of surrounding rock.