Study On The Stability Of Soft And Hard Surrounding Rock Transition Section Of Tunnel Under Drilling And Blasting Method

The drilling and blasting method is widely used in the construction of mountain tunnels,and the drilling and blasting method will cause blasting vibration hazards.Due to the different mechanical properties of different levels of surrounding rock,the impact of blasting vibration load on the deformation and destruction of each level of surrounding rock is different.Based on the study of the dynamic response mechanism and stability during the blasting construction process of the soft and hard surrounding rock transition section of the tunnel,the methods of on-site blasting vibration effect monitoring and numerical simulation are used to analyze the vibration characteristics and fluid-solid coupling effect of the soft and hard surrounding rock transition section,and discuss The propagation and distribution of blasting vibration waves in tunnels are used to analyze the distribution characteristics of seepage field and its influence on the stability of the transition section of weak surrounding rock.The article mainly carried out the following work:1.The blasting vibration curves of the hard rock section,soft rock section and soft-hard transition section of the Laomushan Tunnel are selected for analysis,and the mechanical response mechanism of blasting vibration of different grades of surrounding rock,the change law of the peak blasting vibration velocity and its influence range are studied.It is believed that the propagation of blasting waves in the transition section between soft and hard surrounding rocks is controlled by the magnification of the adjacent surface and the magnification of vertical propagation,and develops from soft rock to hard rock.Compared with the hard rock section and the soft rock section,the transition section There are obvious differences in the law of peak vibration velocity.2.Carry out numerical modeling analysis on the basis of analysis of on-site blasting data,verify the accuracy of the propagation law of blasting waves in the transition section of soft and hard surrounding rock,and study the longitudinal and cross section vibration characteristics of different grades of surrounding rock and its transition section,The mechanical response mechanism of surrounding rock of tunnel blasting vibration is obtained;the peak vibration velocity of different blasting center distances is consistent with the damage affected area,and the peak vibration velocity of the particle induced by blasting has a good correlation with the damage caused by it.3.According to the tunnel drilling and blasting method under different working conditions,use FLAC 3D software to establish the corresponding numerical analysis model to study the transition section between soft and hard surrounding rock under the two working conditions considering the fluid-solid coupling effect and without considering the fluid-solid coupling effect.The change characteristics of seepage field and stress field,and the effect of seepage field on the stability of surrounding rock.The results show that the balance of the seepage field is destroyed after the tunnel excavation.With the tunnel face as the center,the pore water pressure is distributed in a funnel shape,and the pore water pressure change trend is basically consistent with the stress and strain change trend;seepage effect on the soft and hard surrounding rocks of the tunnel The displacement of the transition section has a greater influence.When the fluid-solid coupling effect is considered,the settlement of the arch bottom is closer to the measured value;it is believed that the stability study mechanism of the transition section of soft and hard surrounding rock is essentially due to the stress field and seepage field of the surrounding rock caused by the excavation of the tunnel section.Mutual influence,and work together on the internal rock mass of the tunnel face to make it balance or instability.4.Based on the comparative study of on-site monitoring data and numerical analysis results,based on a comprehensive analysis of the original blasting plan and the original support plan,the blasting source parameters and initial support plan of the excavation section of the soft and hard surrounding rock transition section of the Laomushan Tunnel were analyzed.The optimization is carried out to effectively control the influence of blasting vibration load on the stability of surrounding rock.