Key Technology Of Overbreak Control In Tunnel Blasting Driving

With the rapid development of infrastructure construction in China,the scale of tunnel construction is also increasing.At present,the drilling and blasting method is still mainly used in tunnel excavation,which will inevitably lead to over excavation,and over excavation will not only increase the slag cost,but also increase the support cost.In the past,the over excavation is often directly attributed to not using smooth blasting,but even if some tunnels adopt reasonable smooth blasting,the over excavation phenomenon is still serious.The reason may be that the vibration of cut blasting is too large,resulting in a certain degree of damage to the surrounding rock outside the excavation boundary of the tunnel,resulting in low half hole trace rate of surrounding smooth blasting and serious over excavation.In order to control the over excavation of tunnel blasting excavation,this paper takes the blasting excavation of Wan’an tunnel of Nanchang Ganzhou passenger dedicated line as an example,establishes a mathematical and physical model,and uses theoretical analysis to study the blasting vibration of cut,the main contents are as follows:1.This paper explains the reason why the vibration of cut blasting is too large,which leads to the vibration damage of surrounding rock at the excavation boundary of tunnel,and then leads to the over excavation of surrounding smooth blasting,and gives the criterion of the vibration damage of surrounding rock blasting.2.Under the assumption that the blast resistance line is vertically divided into the center of the explosive charge,the relationship between the inclined angle of the inclined hole and the length of the blast resistance line is derived,and the vibration analysis model of the surrounding rock of the single-stage inclined hole cutting is established;under the assumption that the cutting holes of each stage are evenly distributed and the rock volume of the cutting blasting is fixed,the cutting of the multistage cutting is derived Based on the relationship between the distribution of rock mass under the series and the corresponding series,the vibration analysis model of the surrounding rock with multi-stage inclined hole cutting is established.Under the condition that the smooth blasting holes are evenly distributed around the surrounding rock and the smooth blasting holes block the reflection of the blasting vibration on the propagation path,the ratio relationship between the length of the smooth blasting holes connecting the trench and the semicircle circumference where the center of the smooth blasting holes lies is derived,and the smooth blasting is established Finally,the simplified model of vibration analysis of tunnel cut blasting surrounding rock is established under the condition that the above three assumptions are not mutually exclusive.3.Under the simplified model of vibration analysis of tunnel cut blasting surrounding rock,combined with the Soviet scientist Sadovsky,the Sadovsky formula is induced from the experiment.The theoretical analysis is carried out from three aspects of inclined hole,multi-level cut and smooth blasting hole,and the calculation formula of vibration damage circle of tunnel cut blasting is improved.4.By using the complete calculation formula of vibration damage circle of tunnel surrounding rock cutting blasting,taking the inclination angle of inclined hole,cutting number and vibration reduction rate of smooth blasting hole as variables,the vibration value of cutting blasting under different variables is obtained.Combined with the safety permission line,the vibration damage circle control technology of tunnel surrounding rock cutting blasting is provided for optimizing cutting blasting parameters.5.Combined with the vibration damage circle control technology of tunnel surrounding rock cutting blasting and considering the economic rationality,technical feasibility,safety and efficiency of Wan’an tunnel,the parameters of cutting blasting are optimized for the variable of inclined hole angle,cutting series and smooth blasting hole damping rate,so that the optimal solution guiding the engineering practice of Wan’an tunnel can be found and the parameters are expressed in the form of charts The effect of optimization.