Study On Smooth Blasting Technology Of High-speed Railway Tunnel With Large Fracture Rock Mass

In order to solve the problems of over excavation,under excavation and collapse in the excavation of"large section"and"deep buried"fissured rock mass tunnel,China's tunnel construction is gradually moving towards high efficiency and refinement.In order to better use the smooth wall protection blasting technology in the tunnel blasting of fissured rock mass,it is of great significance to carry out the research on the crack mechanism and law,the optimization of blasting parameters and the effect evaluation of the smooth wall protection blasting of fissured rock mass tunnel,which can provide a new choice for the blasting excavation of fissured rock mass tunnel.In this paper,numerical simulation and field experiments are used to optimize the parameters of smooth blasting in fractured rock tunnel,and a case study is carried out.The main research contents and conclusions are as follows:1)In the intact rock mass,the mechanical behavior of rock under blasting dynamic load and the relationship between the derived crack growth dynamics and blasting technology,charging structure and uncoupling coefficient(k)are studied by means of single hole wall protection blasting.Research shows:(1)The difference between the main crack growth length and the peak value of the particle stress in the reserved side and the throwing side of the conventional smooth blasting is not significant;the main crack length in the reserved side of the smooth wall protection blasting is short,and the opposite is true in the throwing side of the blasting,which shows that the smooth wall protection blasting has a protective effect on the reserved side of the rock mass and a strong crushing effect on the throwing side of the blasting;(2)The number of main cracks is the same between air interval charge and concentrated charge,but the crack growth length of the former is smaller than that of the latter.The main reason is that when air interval charge is used,the explosive is more dispersed along the blast hole length,resulting in the decrease of the peak value of blasting energy;(3)With the increase of the uncoupling coefficient,the stress/displacement of the particles on the side of the retained rock mass and the side wall of the blasting throwing hole decreases gradually,but the growth length of the main cracks on both sides does not show a linear decreasing relationship.When the uncoupling coefficient is 1.56,the failure range of the retained rock mass will be reduced.2)This paper focuses on the relationship between the shothole density coefficient and the main crack growth length under the fissured rock mass.The results show that the relationship between the main crack length and the shothole density coefficient is not linear function,and the shothole density coefficient is 0.82,which is beneficial to the protection of the side rock mass.3)Under the technology of smooth blasting with reserved protective layer,the larger the spacing between holes is,the weaker the radial crack penetration effect between holes is,and the 2.5 times of the blast hole diameter is the best;under the condition of fissured rock mass,the method of smooth blasting with reserved protective layer is feasible,and the thickness of protective layer is 3.75 times of the blast hole diameter,which not only ensures that the protective layer can be effectively broken,but also reduces the degree of damage to the rock above the protective layer When the fracture angle?is about 70 degrees,the impact of blasting cracks on the rock mass above the fracture surface is the smallest.4)According to the characteristics of fracture rock mass in Dingwang tunnel and the results of numerical simulation,this paper puts forward a technology to improve the smooth blasting effect of tunnel.After the technology is put into engineering application,all the data have achieved satisfactory results,compared with the smooth blasting hole mark rate kept above80%,the average overbreak was controlled from 22.46cm to 5.67cm;the average overbreak volume was reduced from 9.55m~3 to 2.41m~3,which improved the current tunnel overbreak Serious under excavation problem;cost saving of 1.51 million yuan per 1km tunnel.