Research On Dynamic Response Of Tunnel Portal Structure Under Blasting Vibration

Tunnel portal is a place prone to safety accidents in tunnel construction.The improper blasting vibration caused by mine construction will induce disasters such as excessive deformation,slope instability,cave collapse and so on.The safety of tunnel portal is always the focus of tunnel engineering.It is of great theoretical and practical significance to research on dynamic response of tunnel portal section under blasting vibration.The research includes the analysis of main factors influencing the safety of tunnel portal and the study of the influence of blasting vibration on the safety and stability of surrounding rock,supporting system and slope.At present,the safety of tunnel portal structure is mainly determined by the peak velocity or acceleration.Under this kind of judgment,the theoretical analysis of structure vibration of tunnel portal section is limited to static analysis.There are insufficient researches about the blasting vibration rules of tunnel portal under its own characteristics and dynamic analysis of surrounding rock,supporting structure and slope of tunnel portal under the action of vibration.In view of this,on the basis of vibration field analysis under cylindrical charge blasting,this thesis focuses on the researches on dynamic response of surrounding slope,supporting structure and slope of tunnel portal section under blasting vibration by means of theoretical analysis,field test and numerical calculation methods.The research methods and contents of tunnel portal structure under blasting vibration at home and abroad are summarized and analyzed.The deficiencies of current research and future development direction are pointed out.Then,the general situation of the research of this thesis is presented based on precious work.The mechanical characteristics of the tunnel portal section are analyzed,and the basic factors affecting the safety and stability of the tunnel portal are analyzed on the basis of the common failure forms of tunnel portals.The propagation rules of the blasting vibration of cylindrical charge in elastic medium are analyzed systematically.The formulas of displacement and stress under the action of vibration propagation are derived.Then the propagation characteristics of blasting vibration of tunnel surrounding rock,supporting structure and slope are analyzed.Based on the principle of energy dissipation,the effect of micro defects on vibration propagation is researched.Then the concept of unit dissipated energy density is proposed and used to modify the rules of blasting vibration of tunnel portal section.The formulas for calculating the dissipated energy density and the velocity field of blasting vibration of the tunnel portal are derived.Based on the principle of dissipation energy density,the accumulative damage problem of the medium under the action of the blasting vibration of the tunnel portal is researched,and the method of calculating the accumulative damage of the medium by the accumulative dissipation energy under vibration is obtained.The dynamic stress of the surrounding rock and supporting structure under blasting vibration is analyzed and calculated The blasting vibration response rules of surrounding rock without support is obtained with parameters including buried depth of tunnel portal,slope angle,tunnel depth and so on.According to the principle of energy dissipation,the safety judgment of surrounding rock without support of tunnel portal is put forward and the safety of supporting structure is discussed.According to the structural characteristics of the tunnel portal slope,the vibration model of slope is established and the dynamic response is analyzed,then the formulas for calculating the dynamic stability safety factors of tunnel portal are carried out.The relationships between the dynamic stability safety factors of tunnel portal slope,tunnel depth,and explosive charge are analyzed through example calculations.The results show that the safety factors of the tunnel portal slope are related to the intensity of blasting vibration,the incident angle,the frequency,the duration,the distance and the system parameters of tunnel structure.